doc/src/sgml/catalogs.sgml

   1 <!-- $PostgreSQL$ -->
   2 <!--
   3  Documentation of the system catalogs, directed toward PostgreSQL developers
   4  -->
   5
   6 <chapter id="catalogs">
   7  <title>System Catalogs</title>
   8
   9   <para>
  10    The system catalogs are the place where a relational database
  11    management system stores schema metadata, such as information about
  12    tables and columns, and internal bookkeeping information.
  13    <productname>PostgreSQL</productname>'s system catalogs are regular
  14    tables.  You can drop and recreate the tables, add columns, insert
  15    and update values, and severely mess up your system that way.
  16    Normally, one should not change the system catalogs by hand, there
  17    are always SQL commands to do that.  (For example, <command>CREATE
  18    DATABASE</command> inserts a row into the
  19    <structname>pg_database</structname> catalog &mdash; and actually
  20    creates the database on disk.)  There are some exceptions for
  21    particularly esoteric operations, such as adding index access methods.
  22   </para>
  23
  24  <sect1 id="catalogs-overview">
  25   <title>Overview</title>
  26
  27   <para>
  28    <xref linkend="catalog-table"> lists the system catalogs.
  29    More detailed documentation of each catalog follows below.
  30   </para>
  31
  32   <para>
  33    Most system catalogs are copied from the template database during
  34    database creation and are thereafter database-specific. A few
  35    catalogs are physically shared across all databases in a cluster;
  36    these are noted in the descriptions of the individual catalogs.
  37   </para>
  38
  39   <table id="catalog-table">
  40    <title>System Catalogs</title>
  41
  42    <tgroup cols="2">
  43     <thead>
  44      <row>
  45       <entry>Catalog Name</entry>
  46       <entry>Purpose</entry>
  47      </row>
  48     </thead>
  49
  50     <tbody>
  51      <row>
  52       <entry><link linkend="catalog-pg-aggregate"><structname>pg_aggregate</structname></link></entry>
  53       <entry>aggregate functions</entry>
  54      </row>
  55
  56      <row>
  57       <entry><link linkend="catalog-pg-am"><structname>pg_am</structname></link></entry>
  58       <entry>index access methods</entry>
  59      </row>
  60
  61      <row>
  62       <entry><link linkend="catalog-pg-amop"><structname>pg_amop</structname></link></entry>
  63       <entry>access method operators</entry>
  64      </row>
  65
  66      <row>
  67       <entry><link linkend="catalog-pg-amproc"><structname>pg_amproc</structname></link></entry>
  68       <entry>access method support procedures</entry>
  69      </row>
  70
  71      <row>
  72       <entry><link linkend="catalog-pg-attrdef"><structname>pg_attrdef</structname></link></entry>
  73       <entry>column default values</entry>
  74      </row>
  75
  76      <row>
  77       <entry><link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link></entry>
  78       <entry>table columns (<quote>attributes</quote>)</entry>
  79      </row>
  80
  81      <row>
  82       <entry><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link></entry>
  83       <entry>authorization identifiers (roles)</entry>
  84      </row>
  85
  86      <row>
  87       <entry><link linkend="catalog-pg-auth-members"><structname>pg_auth_members</structname></link></entry>
  88       <entry>authorization identifier membership relationships</entry>
  89      </row>
  90
  91      <row>
  92       <entry><link linkend="catalog-pg-autovacuum"><structname>pg_autovacuum</structname></link></entry>
  93       <entry>per-relation autovacuum configuration parameters</entry>
  94      </row>
  95
  96      <row>
  97       <entry><link linkend="catalog-pg-cast"><structname>pg_cast</structname></link></entry>
  98       <entry>casts (data type conversions)</entry>
  99      </row>
 100
 101      <row>
 102       <entry><link linkend="catalog-pg-class"><structname>pg_class</structname></link></entry>
 103       <entry>tables, indexes, sequences, views (<quote>relations</quote>)</entry>
 104      </row>
 105
 106      <row>
 107       <entry><link linkend="catalog-pg-constraint"><structname>pg_constraint</structname></link></entry>
 108       <entry>check constraints, unique constraints, primary key constraints, foreign key constraints</entry>
 109      </row>
 110
 111      <row>
 112       <entry><link linkend="catalog-pg-conversion"><structname>pg_conversion</structname></link></entry>
 113       <entry>encoding conversion information</entry>
 114      </row>
 115
 116      <row>
 117       <entry><link linkend="catalog-pg-database"><structname>pg_database</structname></link></entry>
 118       <entry>databases within this database cluster</entry>
 119      </row>
 120
 121      <row>
 122       <entry><link linkend="catalog-pg-depend"><structname>pg_depend</structname></link></entry>
 123       <entry>dependencies between database objects</entry>
 124      </row>
 125
 126      <row>
 127       <entry><link linkend="catalog-pg-description"><structname>pg_description</structname></link></entry>
 128       <entry>descriptions or comments on database objects</entry>
 129      </row>
 130
 131      <row>
 132       <entry><link linkend="catalog-pg-enum"><structname>pg_enum</structname></link></entry>
 133       <entry>enum label and value definitions</entry>
 134      </row>
 135
 136      <row>
 137       <entry><link linkend="catalog-pg-index"><structname>pg_index</structname></link></entry>
 138       <entry>additional index information</entry>
 139      </row>
 140
 141      <row>
 142       <entry><link linkend="catalog-pg-inherits"><structname>pg_inherits</structname></link></entry>
 143       <entry>table inheritance hierarchy</entry>
 144      </row>
 145
 146      <row>
 147       <entry><link linkend="catalog-pg-language"><structname>pg_language</structname></link></entry>
 148       <entry>languages for writing functions</entry>
 149      </row>
 150
 151      <row>
 152       <entry><link linkend="catalog-pg-largeobject"><structname>pg_largeobject</structname></link></entry>
 153       <entry>large objects</entry>
 154      </row>
 155
 156      <row>
 157       <entry><link linkend="catalog-pg-listener"><structname>pg_listener</structname></link></entry>
 158       <entry>asynchronous notification support</entry>
 159      </row>
 160
 161      <row>
 162       <entry><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link></entry>
 163       <entry>schemas</entry>
 164      </row>
 165
 166      <row>
 167       <entry><link linkend="catalog-pg-opclass"><structname>pg_opclass</structname></link></entry>
 168       <entry>access method operator classes</entry>
 169      </row>
 170
 171      <row>
 172       <entry><link linkend="catalog-pg-operator"><structname>pg_operator</structname></link></entry>
 173       <entry>operators</entry>
 174      </row>
 175
 176      <row>
 177       <entry><link linkend="catalog-pg-opfamily"><structname>pg_opfamily</structname></link></entry>
 178       <entry>access method operator families</entry>
 179      </row>
 180
 181      <row>
 182       <entry><link linkend="catalog-pg-pltemplate"><structname>pg_pltemplate</structname></link></entry>
 183       <entry>template data for procedural languages</entry>
 184      </row>
 185
 186      <row>
 187       <entry><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link></entry>
 188       <entry>functions and procedures</entry>
 189      </row>
 190
 191      <row>
 192       <entry><link linkend="catalog-pg-rewrite"><structname>pg_rewrite</structname></link></entry>
 193       <entry>query rewrite rules</entry>
 194      </row>
 195
 196      <row>
 197       <entry><link linkend="catalog-pg-shdepend"><structname>pg_shdepend</structname></link></entry>
 198       <entry>dependencies on shared objects</entry>
 199      </row>
 200
 201      <row>
 202       <entry><link linkend="catalog-pg-shdescription"><structname>pg_shdescription</structname></link></entry>
 203       <entry>comments on shared objects</entry>
 204      </row>
 205
 206      <row>
 207       <entry><link linkend="catalog-pg-statistic"><structname>pg_statistic</structname></link></entry>
 208       <entry>planner statistics</entry>
 209      </row>
 210
 211      <row>
 212       <entry><link linkend="catalog-pg-tablespace"><structname>pg_tablespace</structname></link></entry>
 213       <entry>tablespaces within this database cluster</entry>
 214      </row>
 215
 216      <row>
 217       <entry><link linkend="catalog-pg-trigger"><structname>pg_trigger</structname></link></entry>
 218       <entry>triggers</entry>
 219      </row>
 220
 221      <row>
 222       <entry><link linkend="catalog-pg-ts-config"><structname>pg_ts_config</structname></link></entry>
 223       <entry>text search configurations</entry>
 224      </row>
 225
 226      <row>
 227       <entry><link linkend="catalog-pg-ts-config-map"><structname>pg_ts_config_map</structname></link></entry>
 228       <entry>text search configurations' token mappings</entry>
 229      </row>
 230
 231      <row>
 232       <entry><link linkend="catalog-pg-ts-dict"><structname>pg_ts_dict</structname></link></entry>
 233       <entry>text search dictionaries</entry>
 234      </row>
 235
 236      <row>
 237       <entry><link linkend="catalog-pg-ts-parser"><structname>pg_ts_parser</structname></link></entry>
 238       <entry>text search parsers</entry>
 239      </row>
 240
 241      <row>
 242       <entry><link linkend="catalog-pg-ts-template"><structname>pg_ts_template</structname></link></entry>
 243       <entry>text search templates</entry>
 244      </row>
 245
 246      <row>
 247       <entry><link linkend="catalog-pg-type"><structname>pg_type</structname></link></entry>
 248       <entry>data types</entry>
 249      </row>
 250     </tbody>
 251    </tgroup>
 252   </table>
 253  </sect1>
 254
 255
 256  <sect1 id="catalog-pg-aggregate">
 257   <title><structname>pg_aggregate</structname></title>
 258
 259   <indexterm zone="catalog-pg-aggregate">
 260    <primary>pg_aggregate</primary>
 261   </indexterm>
 262
 263   <para>
 264    The catalog <structname>pg_aggregate</structname> stores information about
 265    aggregate functions.  An aggregate function is a function that
 266    operates on a set of values (typically one column from each row
 267    that matches a query condition) and returns a single value computed
 268    from all these values.  Typical aggregate functions are
 269    <function>sum</function>, <function>count</function>, and
 270    <function>max</function>.  Each entry in
 271    <structname>pg_aggregate</structname> is an extension of an entry
 272    in <structname>pg_proc</structname>.  The <structname>pg_proc</structname>
 273    entry carries the aggregate's name, input and output data types, and
 274    other information that is similar to ordinary functions.
 275   </para>
 276
 277   <table>
 278    <title><structname>pg_aggregate</> Columns</title>
 279
 280    <tgroup cols=4>
 281     <thead>
 282      <row>
 283       <entry>Name</entry>
 284       <entry>Type</entry>
 285       <entry>References</entry>
 286       <entry>Description</entry>
 287      </row>
 288     </thead>
 289     <tbody>
 290      <row>
 291       <entry><structfield>aggfnoid</structfield></entry>
 292       <entry><type>regproc</type></entry>
 293       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
 294       <entry><structname>pg_proc</structname> OID of the aggregate function</entry>
 295      </row>
 296      <row>
 297       <entry><structfield>aggtransfn</structfield></entry>
 298       <entry><type>regproc</type></entry>
 299       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
 300       <entry>Transition function</entry>
 301      </row>
 302      <row>
 303       <entry><structfield>aggfinalfn</structfield></entry>
 304       <entry><type>regproc</type></entry>
 305       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
 306       <entry>Final function (zero if none)</entry>
 307      </row>
 308      <row>
 309       <entry><structfield>aggsortop</structfield></entry>
 310       <entry><type>oid</type></entry>
 311       <entry><literal><link linkend="catalog-pg-operator"><structname>pg_operator</structname></link>.oid</literal></entry>
 312       <entry>Associated sort operator (zero if none)</entry>
 313      </row>
 314      <row>
 315       <entry><structfield>aggtranstype</structfield></entry>
 316       <entry><type>oid</type></entry>
 317       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
 318       <entry>Data type of the aggregate function's internal transition (state) data</entry>
 319      </row>
 320      <row>
 321       <entry><structfield>agginitval</structfield></entry>
 322       <entry><type>text</type></entry>
 323       <entry></entry>
 324       <entry>
 325        The initial value of the transition state.  This is a text
 326        field containing the initial value in its external string
 327        representation.  If this field is NULL, the transition state
 328        value starts out NULL
 329       </entry>
 330      </row>
 331     </tbody>
 332    </tgroup>
 333   </table>
 334
 335   <para>
 336    New aggregate functions are registered with the <xref
 337    linkend="sql-createaggregate" endterm="sql-createaggregate-title">
 338    command.  See <xref linkend="xaggr"> for more information about
 339    writing aggregate functions and the meaning of the transition
 340    functions, etc.
 341   </para>
 342
 343  </sect1>
 344
 345
 346  <sect1 id="catalog-pg-am">
 347   <title><structname>pg_am</structname></title>
 348
 349   <indexterm zone="catalog-pg-am">
 350    <primary>pg_am</primary>
 351   </indexterm>
 352
 353   <para>
 354    The catalog <structname>pg_am</structname> stores information about index
 355    access methods.  There is one row for each index access method supported by
 356    the system.  The contents of this catalog are discussed in detail in
 357    <xref linkend="indexam">.
 358   </para>
 359
 360   <table>
 361    <title><structname>pg_am</> Columns</title>
 362
 363    <tgroup cols=4>
 364     <thead>
 365      <row>
 366       <entry>Name</entry>
 367       <entry>Type</entry>
 368       <entry>References</entry>
 369       <entry>Description</entry>
 370      </row>
 371     </thead>
 372     <tbody>
 373
 374      <row>
 375       <entry><structfield>amname</structfield></entry>
 376       <entry><type>name</type></entry>
 377       <entry></entry>
 378       <entry>Name of the access method</entry>
 379      </row>
 380
 381      <row>
 382       <entry><structfield>amstrategies</structfield></entry>
 383       <entry><type>int2</type></entry>
 384       <entry></entry>
 385       <entry>Number of operator strategies for this access method,
 386        or zero if access method does not have a fixed set of operator
 387        strategies</entry>
 388      </row>
 389
 390      <row>
 391       <entry><structfield>amsupport</structfield></entry>
 392       <entry><type>int2</type></entry>
 393       <entry></entry>
 394       <entry>Number of support routines for this access method</entry>
 395      </row>
 396
 397      <row>
 398       <entry><structfield>amcanorder</structfield></entry>
 399       <entry><type>bool</type></entry>
 400       <entry></entry>
 401       <entry>Does the access method support ordered scans?</entry>
 402      </row>
 403
 404      <row>
 405       <entry><structfield>amcanbackward</structfield></entry>
 406       <entry><type>bool</type></entry>
 407       <entry></entry>
 408       <entry>Does the access method support backward scanning?</entry>
 409      </row>
 410
 411      <row>
 412       <entry><structfield>amcanunique</structfield></entry>
 413       <entry><type>bool</type></entry>
 414       <entry></entry>
 415       <entry>Does the access method support unique indexes?</entry>
 416      </row>
 417
 418      <row>
 419       <entry><structfield>amcanmulticol</structfield></entry>
 420       <entry><type>bool</type></entry>
 421       <entry></entry>
 422       <entry>Does the access method support multicolumn indexes?</entry>
 423      </row>
 424
 425      <row>
 426       <entry><structfield>amoptionalkey</structfield></entry>
 427       <entry><type>bool</type></entry>
 428       <entry></entry>
 429       <entry>Does the access method support a scan without any constraint
 430        for the first index column?</entry>
 431      </row>
 432
 433      <row>
 434       <entry><structfield>amindexnulls</structfield></entry>
 435       <entry><type>bool</type></entry>
 436       <entry></entry>
 437       <entry>Does the access method support null index entries?</entry>
 438      </row>
 439
 440      <row>
 441       <entry><structfield>amsearchnulls</structfield></entry>
 442       <entry><type>bool</type></entry>
 443       <entry></entry>
 444       <entry>Does the access method support IS NULL searches?</entry>
 445      </row>
 446
 447      <row>
 448       <entry><structfield>amstorage</structfield></entry>
 449       <entry><type>bool</type></entry>
 450       <entry></entry>
 451       <entry>Can index storage data type differ from column data type?</entry>
 452      </row>
 453
 454      <row>
 455       <entry><structfield>amclusterable</structfield></entry>
 456       <entry><type>bool</type></entry>
 457       <entry></entry>
 458       <entry>Can an index of this type be clustered on?</entry>
 459      </row>
 460
 461      <row>
 462       <entry><structfield>amkeytype</structfield></entry>
 463       <entry><type>oid</type></entry>
 464       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
 465       <entry>Type of data stored in index, or zero if not a fixed type</entry>
 466      </row>
 467
 468      <row>
 469       <entry><structfield>aminsert</structfield></entry>
 470       <entry><type>regproc</type></entry>
 471       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
 472       <entry><quote>Insert this tuple</quote> function</entry>
 473      </row>
 474
 475      <row>
 476       <entry><structfield>ambeginscan</structfield></entry>
 477       <entry><type>regproc</type></entry>
 478       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
 479       <entry><quote>Start new scan</quote> function</entry>
 480      </row>
 481
 482      <row>
 483       <entry><structfield>amgettuple</structfield></entry>
 484       <entry><type>regproc</type></entry>
 485       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
 486       <entry><quote>Next valid tuple</quote> function</entry>
 487      </row>
 488
 489      <row>
 490       <entry><structfield>amgetbitmap</structfield></entry>
 491       <entry><type>regproc</type></entry>
 492       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
 493       <entry><quote>Fetch all valid tuples</quote> function</entry>
 494      </row>
 495
 496      <row>
 497       <entry><structfield>amrescan</structfield></entry>
 498       <entry><type>regproc</type></entry>
 499       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
 500       <entry><quote>Restart this scan</quote> function</entry>
 501      </row>
 502
 503      <row>
 504       <entry><structfield>amendscan</structfield></entry>
 505       <entry><type>regproc</type></entry>
 506       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
 507       <entry><quote>End this scan</quote> function</entry>
 508      </row>
 509
 510      <row>
 511       <entry><structfield>ammarkpos</structfield></entry>
 512       <entry><type>regproc</type></entry>
 513       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
 514       <entry><quote>Mark current scan position</quote> function</entry>
 515      </row>
 516
 517      <row>
 518       <entry><structfield>amrestrpos</structfield></entry>
 519       <entry><type>regproc</type></entry>
 520       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
 521       <entry><quote>Restore marked scan position</quote> function</entry>
 522      </row>
 523
 524      <row>
 525       <entry><structfield>ambuild</structfield></entry>
 526       <entry><type>regproc</type></entry>
 527       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
 528       <entry><quote>Build new index</quote> function</entry>
 529      </row>
 530
 531      <row>
 532       <entry><structfield>ambulkdelete</structfield></entry>
 533       <entry><type>regproc</type></entry>
 534       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
 535       <entry>Bulk-delete function</entry>
 536      </row>
 537
 538      <row>
 539       <entry><structfield>amvacuumcleanup</structfield></entry>
 540       <entry><type>regproc</type></entry>
 541       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
 542       <entry>Post-<command>VACUUM</command> cleanup function</entry>
 543      </row>
 544
 545      <row>
 546       <entry><structfield>amcostestimate</structfield></entry>
 547       <entry><type>regproc</type></entry>
 548       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
 549       <entry>Function to estimate cost of an index scan</entry>
 550      </row>
 551
 552      <row>
 553       <entry><structfield>amoptions</structfield></entry>
 554       <entry><type>regproc</type></entry>
 555       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
 556       <entry>Function to parse and validate <structfield>reloptions</> for an index</entry>
 557      </row>
 558
 559     </tbody>
 560    </tgroup>
 561   </table>
 562
 563  </sect1>
 564
 565
 566  <sect1 id="catalog-pg-amop">
 567   <title><structname>pg_amop</structname></title>
 568
 569   <indexterm zone="catalog-pg-amop">
 570    <primary>pg_amop</primary>
 571   </indexterm>
 572
 573   <para>
 574    The catalog <structname>pg_amop</structname> stores information about
 575    operators associated with access method operator families.  There is one
 576    row for each operator that is a member of an operator family.  An operator
 577    can appear in more than one family, but cannot appear in more than one
 578    position within a family.
 579   </para>
 580
 581   <table>
 582    <title><structname>pg_amop</> Columns</title>
 583
 584    <tgroup cols=4>
 585     <thead>
 586      <row>
 587       <entry>Name</entry>
 588       <entry>Type</entry>
 589       <entry>References</entry>
 590       <entry>Description</entry>
 591      </row>
 592     </thead>
 593     <tbody>
 594
 595      <row>
 596       <entry><structfield>amopfamily</structfield></entry>
 597       <entry><type>oid</type></entry>
 598       <entry><literal><link linkend="catalog-pg-opfamily"><structname>pg_opfamily</structname></link>.oid</literal></entry>
 599       <entry>The operator family this entry is for</entry>
 600      </row>
 601
 602      <row>
 603       <entry><structfield>amoplefttype</structfield></entry>
 604       <entry><type>oid</type></entry>
 605       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
 606       <entry>Left-hand input data type of operator</entry>
 607      </row>
 608
 609      <row>
 610       <entry><structfield>amoprighttype</structfield></entry>
 611       <entry><type>oid</type></entry>
 612       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
 613       <entry>Right-hand input data type of operator</entry>
 614      </row>
 615
 616      <row>
 617       <entry><structfield>amopstrategy</structfield></entry>
 618       <entry><type>int2</type></entry>
 619       <entry></entry>
 620       <entry>Operator strategy number</entry>
 621      </row>
 622
 623      <row>
 624       <entry><structfield>amopopr</structfield></entry>
 625       <entry><type>oid</type></entry>
 626       <entry><literal><link linkend="catalog-pg-operator"><structname>pg_operator</structname></link>.oid</literal></entry>
 627       <entry>OID of the operator</entry>
 628      </row>
 629
 630      <row>
 631       <entry><structfield>amopmethod</structfield></entry>
 632       <entry><type>oid</type></entry>
 633       <entry><literal><link linkend="catalog-pg-am"><structname>pg_am</structname></link>.oid</literal></entry>
 634       <entry>Index access method operator family is for</entry>
 635      </row>
 636
 637     </tbody>
 638    </tgroup>
 639   </table>
 640
 641   <para>
 642    An entry's <structfield>amopmethod</> must match the
 643    <structname>opfmethod</> of its containing operator family (including
 644    <structfield>amopmethod</> here is an intentional denormalization of the
 645    catalog structure for performance reasons).  Also,
 646    <structfield>amoplefttype</> and <structfield>amoprighttype</> must match
 647    the <structfield>oprleft</> and <structfield>oprright</> fields of the
 648    referenced <structname>pg_operator</> entry.
 649   </para>
 650
 651  </sect1>
 652
 653
 654  <sect1 id="catalog-pg-amproc">
 655   <title><structname>pg_amproc</structname></title>
 656
 657   <indexterm zone="catalog-pg-amproc">
 658    <primary>pg_amproc</primary>
 659   </indexterm>
 660
 661   <para>
 662    The catalog <structname>pg_amproc</structname> stores information about
 663    support procedures associated with access method operator families.  There
 664    is one row for each support procedure belonging to an operator family.
 665   </para>
 666
 667   <table>
 668    <title><structname>pg_amproc</structname> Columns</title>
 669
 670    <tgroup cols=4>
 671     <thead>
 672      <row>
 673       <entry>Name</entry>
 674       <entry>Type</entry>
 675       <entry>References</entry>
 676       <entry>Description</entry>
 677      </row>
 678     </thead>
 679     <tbody>
 680
 681      <row>
 682       <entry><structfield>amprocfamily</structfield></entry>
 683       <entry><type>oid</type></entry>
 684       <entry><literal><link linkend="catalog-pg-opfamily"><structname>pg_opfamily</structname></link>.oid</literal></entry>
 685       <entry>The operator family this entry is for</entry>
 686      </row>
 687
 688      <row>
 689       <entry><structfield>amproclefttype</structfield></entry>
 690       <entry><type>oid</type></entry>
 691       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
 692       <entry>Left-hand input data type of associated operator</entry>
 693      </row>
 694
 695      <row>
 696       <entry><structfield>amprocrighttype</structfield></entry>
 697       <entry><type>oid</type></entry>
 698       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
 699       <entry>Right-hand input data type of associated operator</entry>
 700      </row>
 701
 702      <row>
 703       <entry><structfield>amprocnum</structfield></entry>
 704       <entry><type>int2</type></entry>
 705       <entry></entry>
 706       <entry>Support procedure number</entry>
 707      </row>
 708
 709      <row>
 710       <entry><structfield>amproc</structfield></entry>
 711       <entry><type>regproc</type></entry>
 712       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
 713       <entry>OID of the procedure</entry>
 714      </row>
 715
 716     </tbody>
 717    </tgroup>
 718   </table>
 719
 720   <para>
 721    The usual interpretation of the
 722    <structfield>amproclefttype</> and <structfield>amprocrighttype</> fields
 723    is that they identify the left and right input types of the operator(s)
 724    that a particular support procedure supports.  For some access methods
 725    these match the input data type(s) of the support procedure itself, for
 726    others not.  There is a notion of <quote>default</> support procedures for
 727    an index, which are those with <structfield>amproclefttype</> and
 728    <structfield>amprocrighttype</> both equal to the index opclass's
 729    <structfield>opcintype</>.
 730   </para>
 731
 732  </sect1>
 733
 734
 735  <sect1 id="catalog-pg-attrdef">
 736   <title><structname>pg_attrdef</structname></title>
 737
 738   <indexterm zone="catalog-pg-attrdef">
 739    <primary>pg_attrdef</primary>
 740   </indexterm>
 741
 742   <para>
 743    The catalog <structname>pg_attrdef</structname> stores column default values.  The main information
 744    about columns is stored in <structname>pg_attribute</structname>
 745    (see below).  Only columns that explicitly specify a default value
 746    (when the table is created or the column is added) will have an
 747    entry here.
 748   </para>
 749
 750   <table>
 751    <title><structname>pg_attrdef</> Columns</title>
 752
 753    <tgroup cols=4>
 754     <thead>
 755      <row>
 756       <entry>Name</entry>
 757       <entry>Type</entry>
 758       <entry>References</entry>
 759       <entry>Description</entry>
 760      </row>
 761     </thead>
 762
 763     <tbody>
 764      <row>
 765       <entry><structfield>adrelid</structfield></entry>
 766       <entry><type>oid</type></entry>
 767       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
 768       <entry>The table this column belongs to</entry>
 769      </row>
 770
 771      <row>
 772       <entry><structfield>adnum</structfield></entry>
 773       <entry><type>int2</type></entry>
 774       <entry><literal><link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link>.attnum</literal></entry>
 775       <entry>The number of the column</entry>
 776      </row>
 777
 778      <row>
 779       <entry><structfield>adbin</structfield></entry>
 780       <entry><type>text</type></entry>
 781       <entry></entry>
 782       <entry>The internal representation of the column default value</entry>
 783      </row>
 784
 785      <row>
 786       <entry><structfield>adsrc</structfield></entry>
 787       <entry><type>text</type></entry>
 788       <entry></entry>
 789       <entry>A human-readable representation of the default value</entry>
 790      </row>
 791     </tbody>
 792    </tgroup>
 793   </table>
 794
 795    <para>
 796     The <structfield>adsrc</structfield> field is historical, and is best
 797     not used, because it does not track outside changes that might affect
 798     the representation of the default value.  Reverse-compiling the
 799     <structfield>adbin</structfield> field (with <function>pg_get_expr</> for
 800     example) is a better way to display the default value.
 801    </para>
 802
 803  </sect1>
 804
 805
 806  <sect1 id="catalog-pg-attribute">
 807   <title><structname>pg_attribute</structname></title>
 808
 809   <indexterm zone="catalog-pg-attribute">
 810    <primary>pg_attribute</primary>
 811   </indexterm>
 812
 813   <para>
 814    The catalog <structname>pg_attribute</structname> stores information about
 815    table columns.  There will be exactly one
 816    <structname>pg_attribute</structname> row for every column in every
 817    table in the database.  (There will also be attribute entries for
 818    indexes, and indeed all objects that have <structname>pg_class</structname>
 819    entries.)
 820   </para>
 821
 822   <para>
 823    The term attribute is equivalent to column and is used for
 824    historical reasons.
 825   </para>
 826
 827   <table>
 828    <title><structname>pg_attribute</> Columns</title>
 829
 830    <tgroup cols=4>
 831     <thead>
 832      <row>
 833       <entry>Name</entry>
 834       <entry>Type</entry>
 835       <entry>References</entry>
 836       <entry>Description</entry>
 837      </row>
 838     </thead>
 839
 840     <tbody>
 841      <row>
 842       <entry><structfield>attrelid</structfield></entry>
 843       <entry><type>oid</type></entry>
 844       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
 845       <entry>The table this column belongs to</entry>
 846      </row>
 847
 848      <row>
 849       <entry><structfield>attname</structfield></entry>
 850       <entry><type>name</type></entry>
 851       <entry></entry>
 852       <entry>The column name</entry>
 853      </row>
 854
 855      <row>
 856       <entry><structfield>atttypid</structfield></entry>
 857       <entry><type>oid</type></entry>
 858       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
 859       <entry>The data type of this column</entry>
 860      </row>
 861
 862      <row>
 863       <entry><structfield>attstattarget</structfield></entry>
 864       <entry><type>int4</type></entry>
 865       <entry></entry>
 866       <entry>
 867        <structfield>attstattarget</structfield> controls the level of detail
 868        of statistics accumulated for this column by
 869        <xref linkend="sql-analyze" endterm="sql-analyze-title">.
 870        A zero value indicates that no statistics should be collected.
 871        A negative value says to use the system default statistics target.
 872        The exact meaning of positive values is data type-dependent.
 873        For scalar data types, <structfield>attstattarget</structfield>
 874        is both the target number of <quote>most common values</quote>
 875        to collect, and the target number of histogram bins to create
 876       </entry>
 877      </row>
 878
 879      <row>
 880       <entry><structfield>attlen</structfield></entry>
 881       <entry><type>int2</type></entry>
 882       <entry></entry>
 883       <entry>
 884        A copy of <literal>pg_type.typlen</literal> of this column's
 885        type
 886       </entry>
 887      </row>
 888
 889      <row>
 890       <entry><structfield>attnum</structfield></entry>
 891       <entry><type>int2</type></entry>
 892       <entry></entry>
 893       <entry>
 894        The number of the column.  Ordinary columns are numbered from 1
 895        up.  System columns, such as <structfield>oid</structfield>,
 896        have (arbitrary) negative numbers
 897       </entry>
 898      </row>
 899
 900      <row>
 901       <entry><structfield>attndims</structfield></entry>
 902       <entry><type>int4</type></entry>
 903       <entry></entry>
 904       <entry>
 905        Number of dimensions, if the column is an array type; otherwise 0.
 906        (Presently, the number of dimensions of an array is not enforced,
 907        so any nonzero value effectively means <quote>it's an array</>)
 908       </entry>
 909      </row>
 910
 911      <row>
 912       <entry><structfield>attcacheoff</structfield></entry>
 913       <entry><type>int4</type></entry>
 914       <entry></entry>
 915       <entry>
 916        Always -1 in storage, but when loaded into a row descriptor
 917        in memory this might be updated to cache the offset of the attribute
 918        within the row
 919       </entry>
 920      </row>
 921
 922      <row>
 923       <entry><structfield>atttypmod</structfield></entry>
 924       <entry><type>int4</type></entry>
 925       <entry></entry>
 926       <entry>
 927        <structfield>atttypmod</structfield> records type-specific data
 928        supplied at table creation time (for example, the maximum
 929        length of a <type>varchar</type> column).  It is passed to
 930        type-specific input functions and length coercion functions.
 931        The value will generally be -1 for types that do not need <structfield>atttypmod</>
 932       </entry>
 933      </row>
 934
 935      <row>
 936       <entry><structfield>attbyval</structfield></entry>
 937       <entry><type>bool</type></entry>
 938       <entry></entry>
 939       <entry>
 940        A copy of <literal>pg_type.typbyval</> of this column's type
 941       </entry>
 942      </row>
 943
 944      <row>
 945       <entry><structfield>attstorage</structfield></entry>
 946       <entry><type>char</type></entry>
 947       <entry></entry>
 948       <entry>
 949        Normally a copy of <literal>pg_type.typstorage</> of this
 950        column's type.  For TOAST-able data types, this can be altered
 951        after column creation to control storage policy
 952       </entry>
 953      </row>
 954
 955      <row>
 956       <entry><structfield>attalign</structfield></entry>
 957       <entry><type>char</type></entry>
 958       <entry></entry>
 959       <entry>
 960        A copy of <literal>pg_type.typalign</> of this column's type
 961       </entry>
 962      </row>
 963
 964      <row>
 965       <entry><structfield>attnotnull</structfield></entry>
 966       <entry><type>bool</type></entry>
 967       <entry></entry>
 968       <entry>
 969        This represents a not-null constraint.  It is possible to
 970        change this column to enable or disable the constraint
 971       </entry>
 972      </row>
 973
 974      <row>
 975       <entry><structfield>atthasdef</structfield></entry>
 976       <entry><type>bool</type></entry>
 977       <entry></entry>
 978       <entry>
 979        This column has a default value, in which case there will be a
 980        corresponding entry in the <structname>pg_attrdef</structname>
 981        catalog that actually defines the value
 982       </entry>
 983      </row>
 984
 985      <row>
 986       <entry><structfield>attisdropped</structfield></entry>
 987       <entry><type>bool</type></entry>
 988       <entry></entry>
 989       <entry>
 990        This column has been dropped and is no longer valid.  A dropped
 991        column is still physically present in the table, but is
 992        ignored by the parser and so cannot be accessed via SQL
 993       </entry>
 994      </row>
 995
 996      <row>
 997       <entry><structfield>attislocal</structfield></entry>
 998       <entry><type>bool</type></entry>
 999       <entry></entry>
1000       <entry>
1001        This column is defined locally in the relation.  Note that a column can
1002        be locally defined and inherited simultaneously
1003       </entry>
1004      </row>
1005
1006      <row>
1007       <entry><structfield>attinhcount</structfield></entry>
1008       <entry><type>int4</type></entry>
1009       <entry></entry>
1010       <entry>
1011        The number of direct ancestors this column has.  A column with a
1012        nonzero number of ancestors cannot be dropped nor renamed
1013       </entry>
1014      </row>
1015
1016     </tbody>
1017    </tgroup>
1018   </table>
1019
1020   <para>
1021    In a dropped column's <structname>pg_attribute</structname> entry,
1022    <structfield>atttypid</structfield> is reset to zero, but
1023    <structfield>attlen</structfield> and the other fields copied from
1024    <structname>pg_type</> are still valid.  This arrangement is needed
1025    to cope with the situation where the dropped column's data type was
1026    later dropped, and so there is no <structname>pg_type</> row anymore.
1027    <structfield>attlen</structfield> and the other fields can be used
1028    to interpret the contents of a row of the table.
1029   </para>
1030  </sect1>
1031
1032
1033  <sect1 id="catalog-pg-authid">
1034   <title><structname>pg_authid</structname></title>
1035
1036   <indexterm zone="catalog-pg-authid">
1037    <primary>pg_authid</primary>
1038   </indexterm>
1039
1040   <para>
1041    The catalog <structname>pg_authid</structname> contains information about
1042    database authorization identifiers (roles).  A role subsumes the concepts
1043    of <quote>users</> and <quote>groups</>.  A user is essentially just a
1044    role with the <structfield>rolcanlogin</> flag set.  Any role (with or
1045    without <structfield>rolcanlogin</>) can have other roles as members; see
1046    <link linkend="catalog-pg-auth-members"><structname>pg_auth_members</structname></link>.
1047   </para>
1048
1049   <para>
1050    Since this catalog contains passwords, it must not be publicly readable.
1051    <link linkend="view-pg-roles"><structname>pg_roles</structname></link>
1052    is a publicly readable view on
1053    <structname>pg_authid</structname> that blanks out the password field.
1054   </para>
1055
1056   <para>
1057    <xref linkend="user-manag"> contains detailed information about user and
1058    privilege management.
1059   </para>
1060
1061   <para>
1062    Because user identities are cluster-wide,
1063    <structname>pg_authid</structname>
1064    is shared across all databases of a cluster: there is only one
1065    copy of <structname>pg_authid</structname> per cluster, not
1066    one per database.
1067   </para>
1068
1069   <table>
1070    <title><structname>pg_authid</> Columns</title>
1071
1072    <tgroup cols=3>
1073     <thead>
1074      <row>
1075       <entry>Name</entry>
1076       <entry>Type</entry>
1077       <entry>Description</entry>
1078      </row>
1079     </thead>
1080
1081     <tbody>
1082      <row>
1083       <entry><structfield>rolname</structfield></entry>
1084       <entry><type>name</type></entry>
1085       <entry>Role name</entry>
1086      </row>
1087
1088      <row>
1089       <entry><structfield>rolsuper</structfield></entry>
1090       <entry><type>bool</type></entry>
1091       <entry>Role has superuser privileges</entry>
1092      </row>
1093
1094      <row>
1095       <entry><structfield>rolinherit</structfield></entry>
1096       <entry><type>bool</type></entry>
1097       <entry>Role automatically inherits privileges of roles it is a
1098        member of</entry>
1099      </row>
1100
1101      <row>
1102       <entry><structfield>rolcreaterole</structfield></entry>
1103       <entry><type>bool</type></entry>
1104       <entry>Role can create more roles</entry>
1105      </row>
1106
1107      <row>
1108       <entry><structfield>rolcreatedb</structfield></entry>
1109       <entry><type>bool</type></entry>
1110       <entry>Role can create databases</entry>
1111      </row>
1112
1113      <row>
1114       <entry><structfield>rolcatupdate</structfield></entry>
1115       <entry><type>bool</type></entry>
1116       <entry>
1117        Role can update system catalogs directly.  (Even a superuser cannot do
1118        this unless this column is true)
1119       </entry>
1120      </row>
1121
1122      <row>
1123       <entry><structfield>rolcanlogin</structfield></entry>
1124       <entry><type>bool</type></entry>
1125       <entry>
1126        Role can log in. That is, this role can be given as the initial
1127        session authorization identifier
1128       </entry>
1129      </row>
1130
1131      <row>
1132       <entry><structfield>rolconnlimit</structfield></entry>
1133       <entry><type>int4</type></entry>
1134       <entry>
1135        For roles that can log in, this sets maximum number of concurrent
1136        connections this role can make.  -1 means no limit
1137       </entry>
1138      </row>
1139
1140      <row>
1141       <entry><structfield>rolpassword</structfield></entry>
1142       <entry><type>text</type></entry>
1143       <entry>Password (possibly encrypted); NULL if none</entry>
1144      </row>
1145
1146      <row>
1147       <entry><structfield>rolvaliduntil</structfield></entry>
1148       <entry><type>timestamptz</type></entry>
1149       <entry>Password expiry time (only used for password authentication);
1150        NULL if no expiration</entry>
1151      </row>
1152
1153      <row>
1154       <entry><structfield>rolconfig</structfield></entry>
1155       <entry><type>text[]</type></entry>
1156       <entry>Session defaults for run-time configuration variables</entry>
1157      </row>
1158     </tbody>
1159    </tgroup>
1160   </table>
1161
1162  </sect1>
1163
1164
1165  <sect1 id="catalog-pg-auth-members">
1166   <title><structname>pg_auth_members</structname></title>
1167
1168   <indexterm zone="catalog-pg-auth-members">
1169    <primary>pg_auth_members</primary>
1170   </indexterm>
1171
1172   <para>
1173    The catalog <structname>pg_auth_members</structname> shows the membership
1174    relations between roles.  Any non-circular set of relationships is allowed.
1175   </para>
1176
1177   <para>
1178    Because user identities are cluster-wide,
1179    <structname>pg_auth_members</structname>
1180    is shared across all databases of a cluster: there is only one
1181    copy of <structname>pg_auth_members</structname> per cluster, not
1182    one per database.
1183   </para>
1184
1185   <table>
1186    <title><structname>pg_auth_members</> Columns</title>
1187
1188    <tgroup cols=4>
1189     <thead>
1190      <row>
1191       <entry>Name</entry>
1192       <entry>Type</entry>
1193       <entry>References</entry>
1194       <entry>Description</entry>
1195      </row>
1196     </thead>
1197
1198     <tbody>
1199      <row>
1200       <entry><structfield>roleid</structfield></entry>
1201       <entry><type>oid</type></entry>
1202       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
1203       <entry>ID of a role that has a member</entry>
1204      </row>
1205
1206      <row>
1207       <entry><structfield>member</structfield></entry>
1208       <entry><type>oid</type></entry>
1209       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
1210       <entry>ID of a role that is a member of <structfield>roleid</></entry>
1211      </row>
1212
1213      <row>
1214       <entry><structfield>grantor</structfield></entry>
1215       <entry><type>oid</type></entry>
1216       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
1217       <entry>ID of the role that granted this membership</entry>
1218      </row>
1219
1220      <row>
1221       <entry><structfield>admin_option</structfield></entry>
1222       <entry><type>bool</type></entry>
1223       <entry></entry>
1224       <entry>True if <structfield>member</> can grant membership in
1225        <structfield>roleid</> to others</entry>
1226      </row>
1227     </tbody>
1228    </tgroup>
1229   </table>
1230
1231  </sect1>
1232
1233
1234  <sect1 id="catalog-pg-autovacuum">
1235   <title><structname>pg_autovacuum</structname></title>
1236
1237   <indexterm zone="catalog-pg-autovacuum">
1238    <primary>pg_autovacuum</primary>
1239   </indexterm>
1240
1241   <indexterm zone="catalog-pg-autovacuum">
1242    <primary>autovacuum</primary>
1243    <secondary>table-specific configuration</secondary>
1244   </indexterm>
1245
1246   <para>
1247    The catalog <structname>pg_autovacuum</structname> stores optional
1248    per-relation configuration parameters for the autovacuum daemon.
1249    If there is an entry here for a particular relation, the given
1250    parameters will be used for autovacuuming that table.  If no entry
1251    is present, the system-wide defaults will be used. For more information
1252    about the autovacuum daemon, see <xref linkend="autovacuum">.
1253   </para>
1254
1255   <note>
1256    <para>
1257     It is likely that <structname>pg_autovacuum</structname> will disappear
1258     in a future release, with the information instead being kept in
1259     <structname>pg_class</>.<structfield>reloptions</> entries.
1260    </para>
1261   </note>
1262
1263   <table>
1264    <title><structname>pg_autovacuum</> Columns</title>
1265
1266    <tgroup cols=4>
1267     <thead>
1268      <row>
1269       <entry>Name</entry>
1270       <entry>Type</entry>
1271       <entry>References</entry>
1272       <entry>Description</entry>
1273      </row>
1274     </thead>
1275
1276     <tbody>
1277      <row>
1278       <entry><structfield>vacrelid</structfield></entry>
1279       <entry><type>oid</type></entry>
1280       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
1281       <entry>The table this entry is for</entry>
1282      </row>
1283
1284      <row>
1285       <entry><structfield>enabled</structfield></entry>
1286       <entry><type>bool</type></entry>
1287       <entry></entry>
1288       <entry>If false, this table will not be autovacuumed, except
1289        to prevent transaction ID wraparound</entry>
1290      </row>
1291
1292      <row>
1293       <entry><structfield>vac_base_thresh</structfield></entry>
1294       <entry><type>integer</type></entry>
1295       <entry></entry>
1296       <entry>Minimum number of modified tuples before vacuum</entry>
1297      </row>
1298
1299      <row>
1300       <entry><structfield>vac_scale_factor</structfield></entry>
1301       <entry><type>float4</type></entry>
1302       <entry></entry>
1303       <entry>Multiplier for <structfield>reltuples</> to add to
1304        <structfield>vac_base_thresh</></entry>
1305      </row>
1306
1307      <row>
1308       <entry><structfield>anl_base_thresh</structfield></entry>
1309       <entry><type>integer</type></entry>
1310       <entry></entry>
1311       <entry>Minimum number of modified tuples before analyze</entry>
1312      </row>
1313
1314      <row>
1315       <entry><structfield>anl_scale_factor</structfield></entry>
1316       <entry><type>float4</type></entry>
1317       <entry></entry>
1318       <entry>Multiplier for <structfield>reltuples</> to add to
1319        <structfield>anl_base_thresh</></entry>
1320      </row>
1321
1322      <row>
1323       <entry><structfield>vac_cost_delay</structfield></entry>
1324       <entry><type>integer</type></entry>
1325       <entry></entry>
1326       <entry>Custom <varname>vacuum_cost_delay</> parameter</entry>
1327      </row>
1328
1329      <row>
1330       <entry><structfield>vac_cost_limit</structfield></entry>
1331       <entry><type>integer</type></entry>
1332       <entry></entry>
1333       <entry>Custom <varname>vacuum_cost_limit</> parameter</entry>
1334      </row>
1335
1336      <row>
1337       <entry><structfield>freeze_min_age</structfield></entry>
1338       <entry><type>integer</type></entry>
1339       <entry></entry>
1340       <entry>Custom <varname>vacuum_freeze_min_age</> parameter</entry>
1341      </row>
1342
1343      <row>
1344       <entry><structfield>freeze_max_age</structfield></entry>
1345       <entry><type>integer</type></entry>
1346       <entry></entry>
1347       <entry>Custom <varname>autovacuum_freeze_max_age</> parameter</entry>
1348      </row>
1349     </tbody>
1350    </tgroup>
1351   </table>
1352
1353   <para>
1354    The autovacuum daemon will initiate a <command>VACUUM</> operation
1355    on a particular table when the number of updated or deleted tuples
1356    exceeds <structfield>vac_base_thresh</structfield> plus
1357    <structfield>vac_scale_factor</structfield> times the number of
1358    live tuples currently estimated to be in the relation.
1359    Similarly, it will initiate an <command>ANALYZE</> operation
1360    when the number of inserted, updated or deleted tuples
1361    exceeds <structfield>anl_base_thresh</structfield> plus
1362    <structfield>anl_scale_factor</structfield> times the number of
1363    live tuples currently estimated to be in the relation.
1364   </para>
1365
1366   <para>
1367    Also, the autovacuum daemon will perform a <command>VACUUM</> operation
1368    to prevent transaction ID wraparound if the table's
1369    <structname>pg_class</>.<structfield>relfrozenxid</> field attains an age
1370    of more than <structfield>freeze_max_age</> transactions, whether the table
1371    has been changed or not, even if
1372    <structname>pg_autovacuum</>.<structfield>enabled</> is set to
1373    <literal>false</> for it.  The system will launch autovacuum to perform
1374    such <command>VACUUM</>s even if autovacuum is otherwise disabled.
1375    See <xref linkend="vacuum-for-wraparound"> for more about wraparound
1376    prevention.
1377   </para>
1378
1379   <para>
1380    Any of the numerical fields can contain <literal>-1</> (or indeed
1381    any negative value) to indicate that the system-wide default should
1382    be used for this particular value.  Observe that the
1383    <structfield>vac_cost_delay</> variable inherits its default value from the
1384    <xref linkend="guc-autovacuum-vacuum-cost-delay"> configuration parameter,
1385    or from <xref linkend="guc-vacuum-cost-delay"> if the former is set to a
1386    negative value.  The same applies to <structfield>vac_cost_limit</>.
1387    Also, autovacuum will ignore attempts to set a per-table
1388    <structfield>freeze_max_age</> larger than the system-wide setting (it can
1389    only be set smaller), and the <structfield>freeze_min_age</> value will be
1390    limited to half the system-wide <xref
1391    linkend="guc-autovacuum-freeze-max-age"> setting.  Note that while you
1392    can set <structfield>freeze_max_age</> very small, or even zero, this
1393    is usually unwise since it will force frequent vacuuming.
1394   </para>
1395
1396  </sect1>
1397
1398
1399  <sect1 id="catalog-pg-cast">
1400   <title><structname>pg_cast</structname></title>
1401
1402   <indexterm zone="catalog-pg-cast">
1403    <primary>pg_cast</primary>
1404   </indexterm>
1405
1406   <para>
1407    The catalog <structname>pg_cast</structname> stores data type conversion
1408    paths, both built-in paths and those defined with
1409    <xref linkend="sql-createcast" endterm="sql-createcast-title">.
1410   </para>
1411
1412   <para>
1413    It should be noted that <structname>pg_cast</structname> does not represent
1414    every type conversion that the system knows how to perform; only those that
1415    cannot be deduced from some generic rule.  For example, casting between a
1416    domain and its base type is not explicitly represented in
1417    <structname>pg_cast</structname>.  Another important exception is that
1418    <quote>automatic I/O conversion casts</>, those performed using a data
1419    type's own I/O functions to convert to or from <type>text</> or other
1420    string types, are not explicitly represented in
1421    <structname>pg_cast</structname>.
1422   </para>
1423
1424   <table>
1425    <title><structname>pg_cast</> Columns</title>
1426
1427    <tgroup cols=4>
1428     <thead>
1429      <row>
1430       <entry>Name</entry>
1431       <entry>Type</entry>
1432       <entry>References</entry>
1433       <entry>Description</entry>
1434      </row>
1435     </thead>
1436
1437     <tbody>
1438      <row>
1439       <entry><structfield>castsource</structfield></entry>
1440       <entry><type>oid</type></entry>
1441       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
1442       <entry>OID of the source data type</entry>
1443      </row>
1444
1445      <row>
1446       <entry><structfield>casttarget</structfield></entry>
1447       <entry><type>oid</type></entry>
1448       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
1449       <entry>OID of the target data type</entry>
1450      </row>
1451
1452      <row>
1453       <entry><structfield>castfunc</structfield></entry>
1454       <entry><type>oid</type></entry>
1455       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
1456       <entry>
1457        The OID of the function to use to perform this cast.  Zero is
1458        stored if the cast method doesn't require a function.
1459       </entry>
1460      </row>
1461
1462      <row>
1463       <entry><structfield>castcontext</structfield></entry>
1464       <entry><type>char</type></entry>
1465       <entry></entry>
1466       <entry>
1467        Indicates what contexts the cast can be invoked in.
1468        <literal>e</> means only as an explicit cast (using
1469        <literal>CAST</> or <literal>::</> syntax).
1470        <literal>a</> means implicitly in assignment
1471        to a target column, as well as explicitly.
1472        <literal>i</> means implicitly in expressions, as well as the
1473        other cases
1474       </entry>
1475      </row>
1476      <row>
1477       <entry><structfield>castmethod</structfield></entry>
1478       <entry><type>char</type></entry>
1479       <entry></entry>
1480       <entry>
1481        Indicates how the cast is performed.
1482        <literal>f</> means that the function specified in the <structfield>castfunc</> field is used.
1483        <literal>i</> means that the input/output functions are used.
1484        <literal>b</> means that the types are binary-coercible, thus no conversion is required
1485       </entry>
1486      </row>
1487     </tbody>
1488    </tgroup>
1489   </table>
1490
1491   <para>
1492    The cast functions listed in <structname>pg_cast</structname> must
1493    always take the cast source type as their first argument type, and
1494    return the cast destination type as their result type.  A cast
1495    function can have up to three arguments.  The second argument,
1496    if present, must be type <type>integer</>; it receives the type
1497    modifier associated with the destination type, or <literal>-1</>
1498    if there is none.  The third argument,
1499    if present, must be type <type>boolean</>; it receives <literal>true</>
1500    if the cast is an explicit cast, <literal>false</> otherwise.
1501   </para>
1502
1503   <para>
1504    It is legitimate to create a <structname>pg_cast</structname> entry
1505    in which the source and target types are the same, if the associated
1506    function takes more than one argument.  Such entries represent
1507    <quote>length coercion functions</> that coerce values of the type
1508    to be legal for a particular type modifier value.
1509   </para>
1510
1511   <para>
1512    When a <structname>pg_cast</structname> entry has different source and
1513    target types and a function that takes more than one argument, it
1514    represents converting from one type to another and applying a length
1515    coercion in a single step.  When no such entry is available, coercion
1516    to a type that uses a type modifier involves two steps, one to
1517    convert between data types and a second to apply the modifier.
1518   </para>
1519  </sect1>
1520
1521  <sect1 id="catalog-pg-class">
1522   <title><structname>pg_class</structname></title>
1523
1524   <indexterm zone="catalog-pg-class">
1525    <primary>pg_class</primary>
1526   </indexterm>
1527
1528   <para>
1529    The catalog <structname>pg_class</structname> catalogs tables and most
1530    everything else that has columns or is otherwise similar to a
1531    table.  This includes indexes (but see also
1532    <structname>pg_index</structname>), sequences, views, composite types,
1533    and TOAST tables; see <structfield>relkind</>.
1534    Below, when we mean all of these
1535    kinds of objects we speak of <quote>relations</quote>.  Not all
1536    columns are meaningful for all relation types.
1537   </para>
1538
1539   <table>
1540    <title><structname>pg_class</> Columns</title>
1541
1542    <tgroup cols=4>
1543     <thead>
1544      <row>
1545       <entry>Name</entry>
1546       <entry>Type</entry>
1547       <entry>References</entry>
1548       <entry>Description</entry>
1549      </row>
1550     </thead>
1551
1552     <tbody>
1553      <row>
1554       <entry><structfield>relname</structfield></entry>
1555       <entry><type>name</type></entry>
1556       <entry></entry>
1557       <entry>Name of the table, index, view, etc.</entry>
1558      </row>
1559
1560      <row>
1561       <entry><structfield>relnamespace</structfield></entry>
1562       <entry><type>oid</type></entry>
1563       <entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.oid</literal></entry>
1564       <entry>
1565        The OID of the namespace that contains this relation
1566       </entry>
1567      </row>
1568
1569      <row>
1570       <entry><structfield>reltype</structfield></entry>
1571       <entry><type>oid</type></entry>
1572       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
1573       <entry>
1574        The OID of the data type that corresponds to this table's row type,
1575        if any (zero for indexes, which have no <structname>pg_type</> entry)
1576       </entry>
1577      </row>
1578
1579      <row>
1580       <entry><structfield>relowner</structfield></entry>
1581       <entry><type>oid</type></entry>
1582       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
1583       <entry>Owner of the relation</entry>
1584      </row>
1585
1586      <row>
1587       <entry><structfield>relam</structfield></entry>
1588       <entry><type>oid</type></entry>
1589       <entry><literal><link linkend="catalog-pg-am"><structname>pg_am</structname></link>.oid</literal></entry>
1590       <entry>If this is an index, the access method used (B-tree, hash, etc.)</entry>
1591      </row>
1592
1593      <row>
1594       <entry><structfield>relfilenode</structfield></entry>
1595       <entry><type>oid</type></entry>
1596       <entry></entry>
1597       <entry>Name of the on-disk file of this relation; 0 if none</entry>
1598      </row>
1599
1600      <row>
1601       <entry><structfield>reltablespace</structfield></entry>
1602       <entry><type>oid</type></entry>
1603       <entry><literal><link linkend="catalog-pg-tablespace"><structname>pg_tablespace</structname></link>.oid</literal></entry>
1604       <entry>
1605        The tablespace in which this relation is stored.  If zero,
1606        the database's default tablespace is implied.  (Not meaningful
1607        if the relation has no on-disk file.)
1608       </entry>
1609      </row>
1610
1611      <row>
1612       <entry><structfield>relpages</structfield></entry>
1613       <entry><type>int4</type></entry>
1614       <entry></entry>
1615       <entry>
1616        Size of the on-disk representation of this table in pages (of size
1617        <symbol>BLCKSZ</symbol>).  This is only an estimate used by the
1618        planner.  It is updated by <command>VACUUM</command>,
1619        <command>ANALYZE</command>, and a few DDL commands such as
1620        <command>CREATE INDEX</command>
1621       </entry>
1622      </row>
1623
1624      <row>
1625       <entry><structfield>reltuples</structfield></entry>
1626       <entry><type>float4</type></entry>
1627       <entry></entry>
1628       <entry>
1629        Number of rows in the table.  This is only an estimate used by the
1630        planner.  It is updated by <command>VACUUM</command>,
1631        <command>ANALYZE</command>, and a few DDL commands such as
1632        <command>CREATE INDEX</command>
1633       </entry>
1634      </row>
1635
1636      <row>
1637       <entry><structfield>reltoastrelid</structfield></entry>
1638       <entry><type>oid</type></entry>
1639       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
1640       <entry>
1641        OID of the TOAST table associated with this table, 0 if none.  The
1642        TOAST table stores large attributes <quote>out of line</quote> in a
1643        secondary table
1644       </entry>
1645      </row>
1646
1647      <row>
1648       <entry><structfield>reltoastidxid</structfield></entry>
1649       <entry><type>oid</type></entry>
1650       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
1651       <entry>
1652        For a TOAST table, the OID of its index.  0 if not a TOAST table
1653       </entry>
1654      </row>
1655
1656      <row>
1657       <entry><structfield>relhasindex</structfield></entry>
1658       <entry><type>bool</type></entry>
1659       <entry></entry>
1660       <entry>
1661        True if this is a table and it has (or recently had) any
1662        indexes. This is set by <command>CREATE INDEX</command>, but
1663        not cleared immediately by <command>DROP INDEX</command>.
1664        <command>VACUUM</command> clears <structfield>relhasindex</> if it finds the
1665        table has no indexes
1666       </entry>
1667      </row>
1668
1669      <row>
1670       <entry><structfield>relisshared</structfield></entry>
1671       <entry><type>bool</type></entry>
1672       <entry></entry>
1673       <entry>
1674        True if this table is shared across all databases in the cluster.  Only
1675        certain system catalogs (such as <structname>pg_database</structname>)
1676        are shared
1677       </entry>
1678      </row>
1679
1680      <row>
1681       <entry><structfield>relkind</structfield></entry>
1682       <entry><type>char</type></entry>
1683       <entry></entry>
1684       <entry>
1685        <literal>r</> = ordinary table, <literal>i</> = index,
1686        <literal>S</> = sequence, <literal>v</> = view, <literal>c</> =
1687        composite type, <literal>t</> = TOAST
1688        table
1689       </entry>
1690      </row>
1691
1692      <row>
1693       <entry><structfield>relnatts</structfield></entry>
1694       <entry><type>int2</type></entry>
1695       <entry></entry>
1696       <entry>
1697        Number of user columns in the relation (system columns not
1698        counted).  There must be this many corresponding entries in
1699        <structname>pg_attribute</structname>.  See also
1700        <literal>pg_attribute.attnum</literal>
1701       </entry>
1702      </row>
1703
1704      <row>
1705       <entry><structfield>relchecks</structfield></entry>
1706       <entry><type>int2</type></entry>
1707       <entry></entry>
1708       <entry>
1709        Number of check constraints on the table; see
1710        <link linkend="catalog-pg-constraint"><structname>pg_constraint</structname></link> catalog
1711       </entry>
1712      </row>
1713
1714      <row>
1715       <entry><structfield>reltriggers</structfield></entry>
1716       <entry><type>int2</type></entry>
1717       <entry></entry>
1718       <entry>
1719        Number of triggers on the table; see
1720        <link linkend="catalog-pg-trigger"><structname>pg_trigger</structname></link> catalog
1721       </entry>
1722      </row>
1723
1724      <row>
1725       <entry><structfield>relukeys</structfield></entry>
1726       <entry><type>int2</type></entry>
1727       <entry></entry>
1728       <entry>Unused  (<emphasis>not</emphasis> the number of unique keys)</entry>
1729      </row>
1730
1731      <row>
1732       <entry><structfield>relfkeys</structfield></entry>
1733       <entry><type>int2</type></entry>
1734       <entry></entry>
1735       <entry>Unused  (<emphasis>not</emphasis> the number of foreign keys on the table)</entry>
1736      </row>
1737
1738      <row>
1739       <entry><structfield>relrefs</structfield></entry>
1740       <entry><type>int2</type></entry>
1741       <entry></entry>
1742       <entry>Unused</entry>
1743      </row>
1744
1745      <row>
1746       <entry><structfield>relhasoids</structfield></entry>
1747       <entry><type>bool</type></entry>
1748       <entry></entry>
1749       <entry>
1750        True if we generate an OID for each row of the relation
1751       </entry>
1752      </row>
1753
1754      <row>
1755       <entry><structfield>relhaspkey</structfield></entry>
1756       <entry><type>bool</type></entry>
1757       <entry></entry>
1758       <entry>
1759        True if the table has (or once had) a primary key
1760       </entry>
1761      </row>
1762
1763      <row>
1764       <entry><structfield>relhasrules</structfield></entry>
1765       <entry><type>bool</type></entry>
1766       <entry></entry>
1767       <entry>
1768        True if table has rules; see
1769        <link linkend="catalog-pg-rewrite"><structname>pg_rewrite</structname></link> catalog
1770       </entry>
1771      </row>
1772
1773      <row>
1774       <entry><structfield>relhassubclass</structfield></entry>
1775       <entry><type>bool</type></entry>
1776       <entry></entry>
1777       <entry>True if table has (or once had) any inheritance children</entry>
1778      </row>
1779
1780      <row>
1781       <entry><structfield>relfrozenxid</structfield></entry>
1782       <entry><type>xid</type></entry>
1783       <entry></entry>
1784       <entry>
1785        All transaction IDs before this one have been replaced with a permanent
1786        (<quote>frozen</>) transaction ID in this table.  This is used to track
1787        whether the table needs to be vacuumed in order to prevent transaction
1788        ID wraparound or to allow <literal>pg_clog</> to be shrunk.  Zero
1789        (<symbol>InvalidTransactionId</symbol>) if the relation is not a table
1790       </entry>
1791      </row>
1792
1793      <row>
1794       <entry><structfield>relacl</structfield></entry>
1795       <entry><type>aclitem[]</type></entry>
1796       <entry></entry>
1797       <entry>
1798        Access privileges; see
1799        <xref linkend="sql-grant" endterm="sql-grant-title"> and
1800        <xref linkend="sql-revoke" endterm="sql-revoke-title">
1801        for details
1802       </entry>
1803      </row>
1804
1805      <row>
1806       <entry><structfield>reloptions</structfield></entry>
1807       <entry><type>text[]</type></entry>
1808       <entry></entry>
1809       <entry>
1810        Access-method-specific options, as <quote>keyword=value</> strings
1811       </entry>
1812      </row>
1813     </tbody>
1814    </tgroup>
1815   </table>
1816  </sect1>
1817
1818  <sect1 id="catalog-pg-constraint">
1819   <title><structname>pg_constraint</structname></title>
1820
1821   <indexterm zone="catalog-pg-constraint">
1822    <primary>pg_constraint</primary>
1823   </indexterm>
1824
1825   <para>
1826    The catalog <structname>pg_constraint</structname> stores check, primary key, unique, and foreign
1827    key constraints on tables.  (Column constraints are not treated
1828    specially.  Every column constraint is equivalent to some table
1829    constraint.)  Not-null constraints are represented in the
1830    <structname>pg_attribute</> catalog.
1831   </para>
1832
1833   <para>
1834    Check constraints on domains are stored here, too.
1835   </para>
1836
1837   <table>
1838    <title><structname>pg_constraint</> Columns</title>
1839
1840    <tgroup cols=4>
1841     <thead>
1842      <row>
1843       <entry>Name</entry>
1844       <entry>Type</entry>
1845       <entry>References</entry>
1846       <entry>Description</entry>
1847      </row>
1848     </thead>
1849
1850     <tbody>
1851      <row>
1852       <entry><structfield>conname</structfield></entry>
1853       <entry><type>name</type></entry>
1854       <entry></entry>
1855       <entry>Constraint name (not necessarily unique!)</entry>
1856      </row>
1857
1858      <row>
1859       <entry><structfield>connamespace</structfield></entry>
1860       <entry><type>oid</type></entry>
1861       <entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.oid</literal></entry>
1862       <entry>
1863        The OID of the namespace that contains this constraint
1864       </entry>
1865      </row>
1866
1867      <row>
1868       <entry><structfield>contype</structfield></entry>
1869       <entry><type>char</type></entry>
1870       <entry></entry>
1871       <entry>
1872         <literal>c</> = check constraint,
1873         <literal>f</> = foreign key constraint,
1874         <literal>p</> = primary key constraint,
1875         <literal>u</> = unique constraint
1876       </entry>
1877      </row>
1878
1879      <row>
1880       <entry><structfield>condeferrable</structfield></entry>
1881       <entry><type>bool</type></entry>
1882       <entry></entry>
1883       <entry>Is the constraint deferrable?</entry>
1884      </row>
1885
1886      <row>
1887       <entry><structfield>condeferred</structfield></entry>
1888       <entry><type>bool</type></entry>
1889       <entry></entry>
1890       <entry>Is the constraint deferred by default?</entry>
1891      </row>
1892
1893      <row>
1894       <entry><structfield>conrelid</structfield></entry>
1895       <entry><type>oid</type></entry>
1896       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
1897       <entry>The table this constraint is on; 0 if not a table constraint</entry>
1898      </row>
1899
1900      <row>
1901       <entry><structfield>contypid</structfield></entry>
1902       <entry><type>oid</type></entry>
1903       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
1904       <entry>The domain this constraint is on; 0 if not a domain constraint</entry>
1905      </row>
1906
1907      <row>
1908       <entry><structfield>confrelid</structfield></entry>
1909       <entry><type>oid</type></entry>
1910       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
1911       <entry>If a foreign key, the referenced table; else 0</entry>
1912      </row>
1913
1914      <row>
1915       <entry><structfield>confupdtype</structfield></entry>
1916       <entry><type>char</type></entry>
1917       <entry></entry>
1918       <entry>Foreign key update action code</entry>
1919      </row>
1920
1921      <row>
1922       <entry><structfield>confdeltype</structfield></entry>
1923       <entry><type>char</type></entry>
1924       <entry></entry>
1925       <entry>Foreign key deletion action code</entry>
1926      </row>
1927
1928      <row>
1929       <entry><structfield>confmatchtype</structfield></entry>
1930       <entry><type>char</type></entry>
1931       <entry></entry>
1932       <entry>Foreign key match type</entry>
1933      </row>
1934
1935      <row>
1936       <entry><structfield>conislocal</structfield></entry>
1937       <entry><type>bool</type></entry>
1938       <entry></entry>
1939       <entry>
1940        This constraint is defined locally in the relation.  Note that a
1941        constraint can be locally defined and inherited simultaneously
1942       </entry>
1943      </row>
1944
1945      <row>
1946       <entry><structfield>coninhcount</structfield></entry>
1947       <entry><type>int4</type></entry>
1948       <entry></entry>
1949       <entry>
1950        The number of direct ancestors this constraint has.  A constraint with
1951        a nonzero number of ancestors cannot be dropped nor renamed
1952       </entry>
1953      </row>
1954
1955      <row>
1956       <entry><structfield>conkey</structfield></entry>
1957       <entry><type>int2[]</type></entry>
1958       <entry><literal><link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link>.attnum</></entry>
1959       <entry>If a table constraint, list of columns which the constraint constrains</entry>
1960      </row>
1961
1962      <row>
1963       <entry><structfield>confkey</structfield></entry>
1964       <entry><type>int2[]</type></entry>
1965       <entry><literal><link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link>.attnum</></entry>
1966       <entry>If a foreign key, list of the referenced columns</entry>
1967      </row>
1968
1969      <row>
1970       <entry><structfield>conpfeqop</structfield></entry>
1971       <entry><type>oid[]</type></entry>
1972       <entry><literal><link linkend="catalog-pg-operator"><structname>pg_operator</structname></link>.oid</></entry>
1973       <entry>If a foreign key, list of the equality operators for PK = FK comparisons</entry>
1974      </row>
1975
1976      <row>
1977       <entry><structfield>conppeqop</structfield></entry>
1978       <entry><type>oid[]</type></entry>
1979       <entry><literal><link linkend="catalog-pg-operator"><structname>pg_operator</structname></link>.oid</></entry>
1980       <entry>If a foreign key, list of the equality operators for PK = PK comparisons</entry>
1981      </row>
1982
1983      <row>
1984       <entry><structfield>conffeqop</structfield></entry>
1985       <entry><type>oid[]</type></entry>
1986       <entry><literal><link linkend="catalog-pg-operator"><structname>pg_operator</structname></link>.oid</></entry>
1987       <entry>If a foreign key, list of the equality operators for FK = FK comparisons</entry>
1988      </row>
1989
1990      <row>
1991       <entry><structfield>conbin</structfield></entry>
1992       <entry><type>text</type></entry>
1993       <entry></entry>
1994       <entry>If a check constraint, an internal representation of the expression</entry>
1995      </row>
1996
1997      <row>
1998       <entry><structfield>consrc</structfield></entry>
1999       <entry><type>text</type></entry>
2000       <entry></entry>
2001       <entry>If a check constraint, a human-readable representation of the expression</entry>
2002      </row>
2003     </tbody>
2004    </tgroup>
2005   </table>
2006
2007   <note>
2008    <para>
2009     <structfield>consrc</structfield> is not updated when referenced objects
2010     change; for example, it won't track renaming of columns.  Rather than
2011     relying on this field, it's best to use <function>pg_get_constraintdef()</>
2012     to extract the definition of a check constraint.
2013    </para>
2014   </note>
2015
2016   <note>
2017    <para>
2018     <literal>pg_class.relchecks</literal> needs to agree with the
2019     number of check-constraint entries found in this table for each
2020     relation.
2021    </para>
2022   </note>
2023
2024  </sect1>
2025
2026  <sect1 id="catalog-pg-conversion">
2027   <title><structname>pg_conversion</structname></title>
2028
2029   <indexterm zone="catalog-pg-conversion">
2030    <primary>pg_conversion</primary>
2031   </indexterm>
2032
2033   <para>
2034    The catalog <structname>pg_conversion</structname> describes the
2035    available encoding conversion procedures.  See
2036    <xref linkend="sql-createconversion" endterm="sql-createconversion-title">
2037    for more information.
2038   </para>
2039
2040   <table>
2041    <title><structname>pg_conversion</> Columns</title>
2042
2043    <tgroup cols=4>
2044     <thead>
2045      <row>
2046       <entry>Name</entry>
2047       <entry>Type</entry>
2048       <entry>References</entry>
2049       <entry>Description</entry>
2050      </row>
2051     </thead>
2052
2053     <tbody>
2054      <row>
2055       <entry><structfield>conname</structfield></entry>
2056       <entry><type>name</type></entry>
2057       <entry></entry>
2058       <entry>Conversion name (unique within a namespace)</entry>
2059      </row>
2060
2061      <row>
2062       <entry><structfield>connamespace</structfield></entry>
2063       <entry><type>oid</type></entry>
2064       <entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.oid</literal></entry>
2065       <entry>
2066        The OID of the namespace that contains this conversion
2067       </entry>
2068      </row>
2069
2070      <row>
2071       <entry><structfield>conowner</structfield></entry>
2072       <entry><type>oid</type></entry>
2073       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
2074       <entry>Owner of the conversion</entry>
2075      </row>
2076
2077      <row>
2078       <entry><structfield>conforencoding</structfield></entry>
2079       <entry><type>int4</type></entry>
2080       <entry></entry>
2081       <entry>Source encoding ID</entry>
2082      </row>
2083
2084      <row>
2085       <entry><structfield>contoencoding</structfield></entry>
2086       <entry><type>int4</type></entry>
2087       <entry></entry>
2088       <entry>Destination encoding ID</entry>
2089      </row>
2090
2091      <row>
2092       <entry><structfield>conproc</structfield></entry>
2093       <entry><type>regproc</type></entry>
2094       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
2095       <entry>Conversion procedure</entry>
2096      </row>
2097
2098      <row>
2099       <entry><structfield>condefault</structfield></entry>
2100       <entry><type>bool</type></entry>
2101       <entry></entry>
2102       <entry>True if this is the default conversion</entry>
2103      </row>
2104
2105     </tbody>
2106    </tgroup>
2107   </table>
2108
2109  </sect1>
2110
2111  <sect1 id="catalog-pg-database">
2112   <title><structname>pg_database</structname></title>
2113
2114   <indexterm zone="catalog-pg-database">
2115    <primary>pg_database</primary>
2116   </indexterm>
2117
2118   <para>
2119    The catalog <structname>pg_database</structname> stores information about
2120    the available databases.  Databases are created with the <xref
2121    linkend="sql-createdatabase" endterm="sql-createdatabase-title"> command.
2122    Consult <xref linkend="managing-databases"> for details about the meaning
2123    of some of the parameters.
2124   </para>
2125
2126   <para>
2127    Unlike most system catalogs, <structname>pg_database</structname>
2128    is shared across all databases of a cluster: there is only one
2129    copy of <structname>pg_database</structname> per cluster, not
2130    one per database.
2131   </para>
2132
2133   <table>
2134    <title><structname>pg_database</> Columns</title>
2135
2136    <tgroup cols=4>
2137     <thead>
2138      <row>
2139       <entry>Name</entry>
2140       <entry>Type</entry>
2141       <entry>References</entry>
2142       <entry>Description</entry>
2143      </row>
2144     </thead>
2145
2146     <tbody>
2147      <row>
2148       <entry><structfield>datname</structfield></entry>
2149       <entry><type>name</type></entry>
2150       <entry></entry>
2151       <entry>Database name</entry>
2152      </row>
2153
2154      <row>
2155       <entry><structfield>datdba</structfield></entry>
2156       <entry><type>oid</type></entry>
2157       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
2158       <entry>Owner of the database, usually the user who created it</entry>
2159      </row>
2160
2161      <row>
2162       <entry><structfield>encoding</structfield></entry>
2163       <entry><type>int4</type></entry>
2164       <entry></entry>
2165       <entry>Character encoding for this database
2166           (<function>pg_encoding_to_char()</function> can translate
2167            this number to the encoding name)</entry>
2168      </row>
2169
2170      <row>
2171       <entry><structfield>datcollate</structfield></entry>
2172       <entry><type>name</type></entry>
2173       <entry></entry>
2174       <entry>LC_COLLATE for this database</entry>
2175      </row>
2176
2177      <row>
2178       <entry><structfield>datctype</structfield></entry>
2179       <entry><type>name</type></entry>
2180       <entry></entry>
2181       <entry>LC_CTYPE for this database</entry>
2182      </row>
2183
2184      <row>
2185       <entry><structfield>datistemplate</structfield></entry>
2186       <entry><type>bool</type></entry>
2187       <entry></entry>
2188       <entry>
2189        If true then this database can be used in the
2190        <literal>TEMPLATE</literal> clause of <command>CREATE
2191        DATABASE</command> to create a new database as a clone of
2192        this one
2193       </entry>
2194      </row>
2195
2196      <row>
2197       <entry><structfield>datallowconn</structfield></entry>
2198       <entry><type>bool</type></entry>
2199       <entry></entry>
2200       <entry>
2201        If false then no one can connect to this database.  This is
2202        used to protect the <literal>template0</> database from being altered
2203       </entry>
2204      </row>
2205
2206      <row>
2207       <entry><structfield>datconnlimit</structfield></entry>
2208       <entry><type>int4</type></entry>
2209       <entry></entry>
2210       <entry>
2211        Sets maximum number of concurrent connections that can be made
2212        to this database.  -1 means no limit
2213       </entry>
2214      </row>
2215
2216      <row>
2217       <entry><structfield>datlastsysoid</structfield></entry>
2218       <entry><type>oid</type></entry>
2219       <entry></entry>
2220       <entry>
2221        Last system OID in the database; useful
2222        particularly to <application>pg_dump</application>
2223       </entry>
2224      </row>
2225
2226      <row>
2227       <entry><structfield>datfrozenxid</structfield></entry>
2228       <entry><type>xid</type></entry>
2229       <entry></entry>
2230       <entry>
2231        All transaction IDs before this one have been replaced with a permanent
2232        (<quote>frozen</>) transaction ID in this database.  This is used to
2233        track whether the database needs to be vacuumed in order to prevent
2234        transaction ID wraparound or to allow <literal>pg_clog</> to be shrunk.
2235        It is the minimum of the per-table
2236        <structname>pg_class</>.<structfield>relfrozenxid</> values
2237       </entry>
2238      </row>
2239
2240      <row>
2241       <entry><structfield>dattablespace</structfield></entry>
2242       <entry><type>oid</type></entry>
2243       <entry><literal><link linkend="catalog-pg-tablespace"><structname>pg_tablespace</structname></link>.oid</literal></entry>
2244       <entry>
2245        The default tablespace for the database.
2246        Within this database, all tables for which
2247        <structname>pg_class</>.<structfield>reltablespace</> is zero
2248        will be stored in this tablespace; in particular, all the non-shared
2249        system catalogs will be there
2250       </entry>
2251      </row>
2252
2253      <row>
2254       <entry><structfield>datconfig</structfield></entry>
2255       <entry><type>text[]</type></entry>
2256       <entry></entry>
2257       <entry>Session defaults for run-time configuration variables</entry>
2258      </row>
2259
2260      <row>
2261       <entry><structfield>datacl</structfield></entry>
2262       <entry><type>aclitem[]</type></entry>
2263       <entry></entry>
2264       <entry>
2265        Access privileges; see
2266        <xref linkend="sql-grant" endterm="sql-grant-title"> and
2267        <xref linkend="sql-revoke" endterm="sql-revoke-title">
2268        for details
2269       </entry>
2270      </row>
2271     </tbody>
2272    </tgroup>
2273   </table>
2274  </sect1>
2275
2276
2277  <sect1 id="catalog-pg-depend">
2278   <title><structname>pg_depend</structname></title>
2279
2280   <indexterm zone="catalog-pg-depend">
2281    <primary>pg_depend</primary>
2282   </indexterm>
2283
2284   <para>
2285    The catalog <structname>pg_depend</structname> records the dependency
2286    relationships between database objects.  This information allows
2287    <command>DROP</> commands to find which other objects must be dropped
2288    by <command>DROP CASCADE</> or prevent dropping in the <command>DROP
2289    RESTRICT</> case.
2290   </para>
2291
2292   <para>
2293    See also <link linkend="catalog-pg-shdepend"><structname>pg_shdepend</structname></link>,
2294    which performs a similar function for dependencies involving objects
2295    that are shared across a database cluster.
2296   </para>
2297
2298   <table>
2299    <title><structname>pg_depend</> Columns</title>
2300
2301    <tgroup cols=4>
2302     <thead>
2303      <row>
2304       <entry>Name</entry>
2305       <entry>Type</entry>
2306       <entry>References</entry>
2307       <entry>Description</entry>
2308      </row>
2309     </thead>
2310
2311     <tbody>
2312      <row>
2313       <entry><structfield>classid</structfield></entry>
2314       <entry><type>oid</type></entry>
2315       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
2316       <entry>The OID of the system catalog the dependent object is in</entry>
2317      </row>
2318
2319      <row>
2320       <entry><structfield>objid</structfield></entry>
2321       <entry><type>oid</type></entry>
2322       <entry>any OID column</entry>
2323       <entry>The OID of the specific dependent object</entry>
2324      </row>
2325
2326      <row>
2327       <entry><structfield>objsubid</structfield></entry>
2328       <entry><type>int4</type></entry>
2329       <entry></entry>
2330       <entry>
2331        For a table column, this is the column number (the
2332        <structfield>objid</> and <structfield>classid</> refer to the
2333        table itself).  For all other object types, this column is
2334        zero
2335       </entry>
2336      </row>
2337
2338      <row>
2339       <entry><structfield>refclassid</structfield></entry>
2340       <entry><type>oid</type></entry>
2341       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
2342       <entry>The OID of the system catalog the referenced object is in</entry>
2343      </row>
2344
2345      <row>
2346       <entry><structfield>refobjid</structfield></entry>
2347       <entry><type>oid</type></entry>
2348       <entry>any OID column</entry>
2349       <entry>The OID of the specific referenced object</entry>
2350      </row>
2351
2352      <row>
2353       <entry><structfield>refobjsubid</structfield></entry>
2354       <entry><type>int4</type></entry>
2355       <entry></entry>
2356       <entry>
2357        For a table column, this is the column number (the
2358        <structfield>refobjid</> and <structfield>refclassid</> refer
2359        to the table itself).  For all other object types, this column
2360        is zero
2361       </entry>
2362      </row>
2363
2364      <row>
2365       <entry><structfield>deptype</structfield></entry>
2366       <entry><type>char</type></entry>
2367       <entry></entry>
2368       <entry>
2369        A code defining the specific semantics of this dependency relationship; see text
2370       </entry>
2371      </row>
2372
2373     </tbody>
2374    </tgroup>
2375   </table>
2376
2377   <para>
2378    In all cases, a <structname>pg_depend</structname> entry indicates that the
2379    referenced object cannot be dropped without also dropping the dependent
2380    object.  However, there are several subflavors identified by
2381    <structfield>deptype</>:
2382
2383    <variablelist>
2384     <varlistentry>
2385      <term><symbol>DEPENDENCY_NORMAL</> (<literal>n</>)</term>
2386      <listitem>
2387       <para>
2388        A normal relationship between separately-created objects.  The
2389        dependent object can be dropped without affecting the
2390        referenced object.  The referenced object can only be dropped
2391        by specifying <literal>CASCADE</>, in which case the dependent
2392        object is dropped, too.  Example: a table column has a normal
2393        dependency on its data type.
2394       </para>
2395      </listitem>
2396     </varlistentry>
2397
2398     <varlistentry>
2399      <term><symbol>DEPENDENCY_AUTO</> (<literal>a</>)</term>
2400      <listitem>
2401       <para>
2402        The dependent object can be dropped separately from the
2403        referenced object, and should be automatically dropped
2404        (regardless of <literal>RESTRICT</> or <literal>CASCADE</>
2405        mode) if the referenced object is dropped.  Example: a named
2406        constraint on a table is made autodependent on the table, so
2407        that it will go away if the table is dropped.
2408       </para>
2409      </listitem>
2410     </varlistentry>
2411
2412     <varlistentry>
2413      <term><symbol>DEPENDENCY_INTERNAL</> (<literal>i</>)</term>
2414      <listitem>
2415       <para>
2416        The dependent object was created as part of creation of the
2417        referenced object, and is really just a part of its internal
2418        implementation.  A <command>DROP</> of the dependent object
2419        will be disallowed outright (we'll tell the user to issue a
2420        <command>DROP</> against the referenced object, instead).  A
2421        <command>DROP</> of the referenced object will be propagated
2422        through to drop the dependent object whether
2423        <command>CASCADE</> is specified or not.  Example: a trigger
2424        that's created to enforce a foreign-key constraint is made
2425        internally dependent on the constraint's
2426        <structname>pg_constraint</> entry.
2427       </para>
2428      </listitem>
2429     </varlistentry>
2430
2431     <varlistentry>
2432      <term><symbol>DEPENDENCY_PIN</> (<literal>p</>)</term>
2433      <listitem>
2434       <para>
2435        There is no dependent object; this type of entry is a signal
2436        that the system itself depends on the referenced object, and so
2437        that object must never be deleted.  Entries of this type are
2438        created only by <command>initdb</command>.  The columns for the
2439        dependent object contain zeroes.
2440       </para>
2441      </listitem>
2442     </varlistentry>
2443    </variablelist>
2444
2445    Other dependency flavors might be needed in future.
2446   </para>
2447
2448  </sect1>
2449
2450
2451  <sect1 id="catalog-pg-description">
2452   <title><structname>pg_description</structname></title>
2453
2454   <indexterm zone="catalog-pg-description">
2455    <primary>pg_description</primary>
2456   </indexterm>
2457
2458   <para>
2459    The catalog <structname>pg_description</> stores optional descriptions
2460    (comments) for each database object.  Descriptions can be manipulated
2461    with the <xref linkend="sql-comment" endterm="sql-comment-title"> command and viewed with
2462    <application>psql</application>'s <literal>\d</literal> commands.
2463    Descriptions of many built-in system objects are provided in the initial
2464    contents of <structname>pg_description</structname>.
2465   </para>
2466
2467   <para>
2468    See also <link linkend="catalog-pg-shdescription"><structname>pg_shdescription</structname></link>,
2469    which performs a similar function for descriptions involving objects that
2470    are shared across a database cluster.
2471   </para>
2472
2473   <table>
2474    <title><structname>pg_description</> Columns</title>
2475
2476    <tgroup cols=4>
2477     <thead>
2478      <row>
2479       <entry>Name</entry>
2480       <entry>Type</entry>
2481       <entry>References</entry>
2482       <entry>Description</entry>
2483      </row>
2484     </thead>
2485
2486     <tbody>
2487      <row>
2488       <entry><structfield>objoid</structfield></entry>
2489       <entry><type>oid</type></entry>
2490       <entry>any OID column</entry>
2491       <entry>The OID of the object this description pertains to</entry>
2492      </row>
2493
2494      <row>
2495       <entry><structfield>classoid</structfield></entry>
2496       <entry><type>oid</type></entry>
2497       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
2498       <entry>The OID of the system catalog this object appears in</entry>
2499      </row>
2500
2501      <row>
2502       <entry><structfield>objsubid</structfield></entry>
2503       <entry><type>int4</type></entry>
2504       <entry></entry>
2505       <entry>
2506        For a comment on a table column, this is the column number (the
2507        <structfield>objoid</> and <structfield>classoid</> refer to
2508        the table itself).  For all other object types, this column is
2509        zero
2510       </entry>
2511      </row>
2512
2513      <row>
2514       <entry><structfield>description</structfield></entry>
2515       <entry><type>text</type></entry>
2516       <entry></entry>
2517       <entry>Arbitrary text that serves as the description of this object</entry>
2518      </row>
2519     </tbody>
2520    </tgroup>
2521   </table>
2522
2523  </sect1>
2524
2525
2526  <sect1 id="catalog-pg-enum">
2527   <title><structname>pg_enum</structname></title>
2528
2529   <indexterm zone="catalog-pg-enum">
2530    <primary>pg_enum</primary>
2531   </indexterm>
2532
2533   <para>
2534    The <structname>pg_enum</structname> catalog contains entries
2535    matching enum types to their associated values and labels. The
2536    internal representation of a given enum value is actually the OID
2537    of its associated row in <structname>pg_enum</structname>.  The
2538    OIDs for a particular enum type are guaranteed to be ordered in
2539    the way the type should sort, but there is no guarantee about the
2540    ordering of OIDs of unrelated enum types.
2541   </para>
2542
2543   <table>
2544    <title><structname>pg_enum</> Columns</title>
2545
2546    <tgroup cols=4>
2547     <thead>
2548      <row>
2549       <entry>Name</entry>
2550       <entry>Type</entry>
2551       <entry>References</entry>
2552       <entry>Description</entry>
2553      </row>
2554     </thead>
2555
2556     <tbody>
2557      <row>
2558       <entry><structfield>enumtypid</structfield></entry>
2559       <entry><type>oid</type></entry>
2560       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
2561       <entry>The OID of the <structname>pg_type</> entry owning this enum value</entry>
2562      </row>
2563
2564      <row>
2565       <entry><structfield>enumlabel</structfield></entry>
2566       <entry><type>name</type></entry>
2567       <entry></entry>
2568       <entry>The textual label for this enum value</entry>
2569      </row>
2570     </tbody>
2571    </tgroup>
2572   </table>
2573  </sect1>
2574
2575
2576  <sect1 id="catalog-pg-index">
2577   <title><structname>pg_index</structname></title>
2578
2579   <indexterm zone="catalog-pg-index">
2580    <primary>pg_index</primary>
2581   </indexterm>
2582
2583   <para>
2584    The catalog <structname>pg_index</structname> contains part of the information
2585    about indexes.  The rest is mostly in
2586    <structname>pg_class</structname>.
2587   </para>
2588
2589   <table>
2590    <title><structname>pg_index</> Columns</title>
2591
2592    <tgroup cols=4>
2593     <thead>
2594      <row>
2595       <entry>Name</entry>
2596       <entry>Type</entry>
2597       <entry>References</entry>
2598       <entry>Description</entry>
2599      </row>
2600     </thead>
2601
2602     <tbody>
2603      <row>
2604       <entry><structfield>indexrelid</structfield></entry>
2605       <entry><type>oid</type></entry>
2606       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
2607       <entry>The OID of the <structname>pg_class</> entry for this index</entry>
2608      </row>
2609
2610      <row>
2611       <entry><structfield>indrelid</structfield></entry>
2612       <entry><type>oid</type></entry>
2613       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
2614       <entry>The OID of the <structname>pg_class</> entry for the table this index is for</entry>
2615      </row>
2616
2617      <row>
2618       <entry><structfield>indnatts</structfield></entry>
2619       <entry><type>int2</type></entry>
2620       <entry></entry>
2621       <entry>The number of columns in the index (duplicates
2622       <literal>pg_class.relnatts</literal>)</entry>
2623      </row>
2624
2625      <row>
2626       <entry><structfield>indisunique</structfield></entry>
2627       <entry><type>bool</type></entry>
2628       <entry></entry>
2629       <entry>If true, this is a unique index</entry>
2630      </row>
2631
2632      <row>
2633       <entry><structfield>indisprimary</structfield></entry>
2634       <entry><type>bool</type></entry>
2635       <entry></entry>
2636       <entry>If true, this index represents the primary key of the table
2637       (<structfield>indisunique</> should always be true when this is true)</entry>
2638      </row>
2639
2640      <row>
2641       <entry><structfield>indisclustered</structfield></entry>
2642       <entry><type>bool</type></entry>
2643       <entry></entry>
2644       <entry>If true, the table was last clustered on this index</entry>
2645      </row>
2646
2647      <row>
2648       <entry><structfield>indisvalid</structfield></entry>
2649       <entry><type>bool</type></entry>
2650       <entry></entry>
2651       <entry>
2652        If true, the index is currently valid for queries.  False means the
2653        index is possibly incomplete: it must still be modified by
2654        <command>INSERT</>/<command>UPDATE</> operations, but it cannot safely
2655        be used for queries. If it is unique, the uniqueness property is not
2656        true either
2657       </entry>
2658      </row>
2659
2660      <row>
2661       <entry><structfield>indcheckxmin</structfield></entry>
2662       <entry><type>bool</type></entry>
2663       <entry></entry>
2664       <entry>
2665        If true, queries must not use the index until the <structfield>xmin</>
2666        of this <structname>pg_index</> row is below their TransactionXmin
2667        event horizon, because the table may contain broken HOT chains with
2668        incompatible rows that they can see
2669       </entry>
2670      </row>
2671
2672      <row>
2673       <entry><structfield>indisready</structfield></entry>
2674       <entry><type>bool</type></entry>
2675       <entry></entry>
2676       <entry>
2677        If true, the index is currently ready for inserts.  False means the
2678        index must be ignored by <command>INSERT</>/<command>UPDATE</>
2679        operations
2680       </entry>
2681      </row>
2682
2683      <row>
2684       <entry><structfield>indkey</structfield></entry>
2685       <entry><type>int2vector</type></entry>
2686       <entry><literal><link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link>.attnum</literal></entry>
2687       <entry>
2688        This is an array of <structfield>indnatts</structfield> values that
2689        indicate which table columns this index indexes.  For example a value
2690        of <literal>1 3</literal> would mean that the first and the third table
2691        columns make up the index key.  A zero in this array indicates that the
2692        corresponding index attribute is an expression over the table columns,
2693        rather than a simple column reference
2694       </entry>
2695      </row>
2696
2697      <row>
2698       <entry><structfield>indclass</structfield></entry>
2699       <entry><type>oidvector</type></entry>
2700       <entry><literal><link linkend="catalog-pg-opclass"><structname>pg_opclass</structname></link>.oid</literal></entry>
2701       <entry>
2702        For each column in the index key, this contains the OID of
2703        the operator class to use.  See
2704        <link linkend="catalog-pg-opclass"><structname>pg_opclass</structname></link> for details
2705       </entry>
2706      </row>
2707
2708      <row>
2709       <entry><structfield>indoption</structfield></entry>
2710       <entry><type>int2vector</type></entry>
2711       <entry></entry>
2712       <entry>
2713        This is an array of <structfield>indnatts</structfield> values that
2714        store per-column flag bits.  The meaning of the bits is defined by
2715        the index's access method
2716       </entry>
2717      </row>
2718
2719      <row>
2720       <entry><structfield>indexprs</structfield></entry>
2721       <entry><type>text</type></entry>
2722       <entry></entry>
2723       <entry>Expression trees (in <function>nodeToString()</function> representation)
2724       for index attributes that are not simple column references.  This is a
2725       list with one element for each zero entry in <structfield>indkey</>.
2726       NULL if all index attributes are simple references</entry>
2727      </row>
2728
2729      <row>
2730       <entry><structfield>indpred</structfield></entry>
2731       <entry><type>text</type></entry>
2732       <entry></entry>
2733       <entry>Expression tree (in <function>nodeToString()</function> representation)
2734       for partial index predicate.  NULL if not a partial index</entry>
2735      </row>
2736     </tbody>
2737    </tgroup>
2738   </table>
2739
2740  </sect1>
2741
2742
2743  <sect1 id="catalog-pg-inherits">
2744   <title><structname>pg_inherits</structname></title>
2745
2746   <indexterm zone="catalog-pg-inherits">
2747    <primary>pg_inherits</primary>
2748   </indexterm>
2749
2750   <para>
2751    The catalog <structname>pg_inherits</> records information about
2752    table inheritance hierarchies.  There is one entry for each direct
2753    child table in the database.  (Indirect inheritance can be determined
2754    by following chains of entries.)
2755   </para>
2756
2757   <table>
2758    <title><structname>pg_inherits</> Columns</title>
2759
2760    <tgroup cols=4>
2761     <thead>
2762      <row>
2763       <entry>Name</entry>
2764       <entry>Type</entry>
2765       <entry>References</entry>
2766       <entry>Description</entry>
2767      </row>
2768     </thead>
2769
2770     <tbody>
2771      <row>
2772       <entry><structfield>inhrelid</structfield></entry>
2773       <entry><type>oid</type></entry>
2774       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
2775       <entry>
2776        The OID of the child table
2777       </entry>
2778      </row>
2779
2780      <row>
2781       <entry><structfield>inhparent</structfield></entry>
2782       <entry><type>oid</type></entry>
2783       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
2784       <entry>
2785        The OID of the parent table
2786       </entry>
2787      </row>
2788
2789      <row>
2790       <entry><structfield>inhseqno</structfield></entry>
2791       <entry><type>int4</type></entry>
2792       <entry></entry>
2793       <entry>
2794        If there is more than one direct parent for a child table (multiple
2795        inheritance), this number tells the order in which the
2796        inherited columns are to be arranged.  The count starts at 1
2797       </entry>
2798      </row>
2799     </tbody>
2800    </tgroup>
2801   </table>
2802
2803  </sect1>
2804
2805
2806  <sect1 id="catalog-pg-language">
2807   <title><structname>pg_language</structname></title>
2808
2809   <indexterm zone="catalog-pg-language">
2810    <primary>pg_language</primary>
2811   </indexterm>
2812
2813   <para>
2814    The catalog <structname>pg_language</structname> registers
2815    languages in which you can write functions or stored procedures.
2816    See <xref linkend="sql-createlanguage" endterm="sql-createlanguage-title">
2817    and <xref linkend="xplang"> for more information about language handlers.
2818   </para>
2819
2820   <table>
2821    <title><structname>pg_language</> Columns</title>
2822
2823    <tgroup cols=4>
2824     <thead>
2825      <row>
2826       <entry>Name</entry>
2827       <entry>Type</entry>
2828       <entry>References</entry>
2829       <entry>Description</entry>
2830      </row>
2831     </thead>
2832
2833     <tbody>
2834      <row>
2835       <entry><structfield>lanname</structfield></entry>
2836       <entry><type>name</type></entry>
2837       <entry></entry>
2838       <entry>Name of the language</entry>
2839      </row>
2840
2841      <row>
2842       <entry><structfield>lanowner</structfield></entry>
2843       <entry><type>oid</type></entry>
2844       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
2845       <entry>Owner of the language</entry>
2846      </row>
2847
2848      <row>
2849       <entry><structfield>lanispl</structfield></entry>
2850       <entry><type>bool</type></entry>
2851       <entry></entry>
2852       <entry>
2853        This is false for internal languages (such as
2854        <acronym>SQL</acronym>) and true for user-defined languages.
2855        Currently, <application>pg_dump</application> still uses this
2856        to determine which languages need to be dumped, but this might be
2857        replaced by a different mechanism in the future
2858       </entry>
2859      </row>
2860
2861      <row>
2862       <entry><structfield>lanpltrusted</structfield></entry>
2863       <entry><type>bool</type></entry>
2864       <entry></entry>
2865       <entry>
2866        True if this is a trusted language, which means that it is believed
2867        not to grant access to anything outside the normal SQL execution
2868        environment.  Only superusers can create functions in untrusted
2869        languages
2870       </entry>
2871      </row>
2872
2873      <row>
2874       <entry><structfield>lanplcallfoid</structfield></entry>
2875       <entry><type>oid</type></entry>
2876       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
2877       <entry>
2878        For noninternal languages this references the language
2879        handler, which is a special function that is responsible for
2880        executing all functions that are written in the particular
2881        language
2882       </entry>
2883      </row>
2884
2885      <row>
2886       <entry><structfield>lanvalidator</structfield></entry>
2887       <entry><type>oid</type></entry>
2888       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
2889       <entry>
2890        This references a language validator function that is responsible
2891        for checking the syntax and validity of new functions when they
2892        are created.  Zero if no validator is provided
2893       </entry>
2894      </row>
2895
2896      <row>
2897       <entry><structfield>lanacl</structfield></entry>
2898       <entry><type>aclitem[]</type></entry>
2899       <entry></entry>
2900       <entry>
2901        Access privileges; see
2902        <xref linkend="sql-grant" endterm="sql-grant-title"> and
2903        <xref linkend="sql-revoke" endterm="sql-revoke-title">
2904        for details
2905       </entry>
2906      </row>
2907     </tbody>
2908    </tgroup>
2909   </table>
2910
2911  </sect1>
2912
2913
2914  <sect1 id="catalog-pg-largeobject">
2915   <title><structname>pg_largeobject</structname></title>
2916
2917   <indexterm zone="catalog-pg-largeobject">
2918    <primary>pg_largeobject</primary>
2919   </indexterm>
2920
2921   <para>
2922    The catalog <structname>pg_largeobject</structname> holds the data making up
2923    <quote>large objects</quote>.  A large object is identified by an
2924    OID assigned when it is created.  Each large object is broken into
2925    segments or <quote>pages</> small enough to be conveniently stored as rows
2926    in <structname>pg_largeobject</structname>.
2927    The amount of data per page is defined to be <symbol>LOBLKSIZE</> (which is currently
2928    <literal>BLCKSZ/4</>, or typically 2 kB).
2929   </para>
2930
2931   <table>
2932    <title><structname>pg_largeobject</> Columns</title>
2933
2934    <tgroup cols=3>
2935     <thead>
2936      <row>
2937       <entry>Name</entry>
2938       <entry>Type</entry>
2939       <entry>Description</entry>
2940      </row>
2941     </thead>
2942
2943     <tbody>
2944      <row>
2945       <entry><structfield>loid</structfield></entry>
2946       <entry><type>oid</type></entry>
2947       <entry>Identifier of the large object that includes this page</entry>
2948      </row>
2949
2950      <row>
2951       <entry><structfield>pageno</structfield></entry>
2952       <entry><type>int4</type></entry>
2953       <entry>Page number of this page within its large object
2954       (counting from zero)</entry>
2955      </row>
2956
2957      <row>
2958       <entry><structfield>data</structfield></entry>
2959       <entry><type>bytea</type></entry>
2960       <entry>
2961        Actual data stored in the large object.
2962        This will never be more than <symbol>LOBLKSIZE</> bytes and might be less
2963       </entry>
2964      </row>
2965     </tbody>
2966    </tgroup>
2967   </table>
2968
2969   <para>
2970    Each row of <structname>pg_largeobject</structname> holds data
2971    for one page of a large object, beginning at
2972    byte offset (<literal>pageno * LOBLKSIZE</>) within the object.  The implementation
2973    allows sparse storage: pages might be missing, and might be shorter than
2974    <literal>LOBLKSIZE</> bytes even if they are not the last page of the object.
2975    Missing regions within a large object read as zeroes.
2976   </para>
2977
2978  </sect1>
2979
2980
2981  <sect1 id="catalog-pg-listener">
2982   <title><structname>pg_listener</structname></title>
2983
2984   <indexterm zone="catalog-pg-listener">
2985    <primary>pg_listener</primary>
2986   </indexterm>
2987
2988   <para>
2989    The catalog <structname>pg_listener</structname> supports the
2990    <xref linkend="sql-listen" endterm="sql-listen-title"> and
2991    <xref linkend="sql-notify" endterm="sql-notify-title">
2992    commands.  A listener creates an entry in
2993    <structname>pg_listener</structname> for each notification name
2994    it is listening for.  A notifier scans <structname>pg_listener</structname>
2995    and updates each matching entry to show that a notification has occurred.
2996    The notifier also sends a signal (using the PID recorded in the table)
2997    to awaken the listener from sleep.
2998   </para>
2999
3000   <table>
3001    <title><structname>pg_listener</> Columns</title>
3002
3003    <tgroup cols=4>
3004     <thead>
3005      <row>
3006       <entry>Name</entry>
3007       <entry>Type</entry>
3008       <entry>References</entry>
3009       <entry>Description</entry>
3010      </row>
3011     </thead>
3012
3013     <tbody>
3014      <row>
3015       <entry><structfield>relname</structfield></entry>
3016       <entry><type>name</type></entry>
3017       <entry>
3018        Notify condition name.  (The name need not match any actual
3019        relation in the database; the name <structfield>relname</> is historical.)
3020       </entry>
3021      </row>
3022
3023      <row>
3024       <entry><structfield>listenerpid</structfield></entry>
3025       <entry><type>int4</type></entry>
3026       <entry>PID of the server process that created this entry</entry>
3027      </row>
3028
3029      <row>
3030       <entry><structfield>notification</structfield></entry>
3031       <entry><type>int4</type></entry>
3032       <entry>
3033        Zero if no event is pending for this listener.  If an event is
3034        pending, the PID of the server process that sent the notification
3035       </entry>
3036      </row>
3037     </tbody>
3038    </tgroup>
3039   </table>
3040
3041  </sect1>
3042
3043
3044  <sect1 id="catalog-pg-namespace">
3045   <title><structname>pg_namespace</structname></title>
3046
3047   <indexterm zone="catalog-pg-namespace">
3048    <primary>pg_namespace</primary>
3049   </indexterm>
3050
3051   <para>
3052    The catalog <structname>pg_namespace</> stores namespaces.
3053    A namespace is the structure underlying SQL schemas: each namespace
3054    can have a separate collection of relations, types, etc. without name
3055    conflicts.
3056   </para>
3057
3058   <table>
3059    <title><structname>pg_namespace</> Columns</title>
3060
3061    <tgroup cols=4>
3062     <thead>
3063      <row>
3064       <entry>Name</entry>
3065       <entry>Type</entry>
3066       <entry>References</entry>
3067       <entry>Description</entry>
3068      </row>
3069     </thead>
3070
3071     <tbody>
3072      <row>
3073       <entry><structfield>nspname</structfield></entry>
3074       <entry><type>name</type></entry>
3075       <entry></entry>
3076       <entry>Name of the namespace</entry>
3077      </row>
3078
3079      <row>
3080       <entry><structfield>nspowner</structfield></entry>
3081       <entry><type>oid</type></entry>
3082       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
3083       <entry>Owner of the namespace</entry>
3084      </row>
3085
3086      <row>
3087       <entry><structfield>nspacl</structfield></entry>
3088       <entry><type>aclitem[]</type></entry>
3089       <entry></entry>
3090       <entry>
3091        Access privileges; see
3092        <xref linkend="sql-grant" endterm="sql-grant-title"> and
3093        <xref linkend="sql-revoke" endterm="sql-revoke-title">
3094        for details
3095       </entry>
3096      </row>
3097     </tbody>
3098    </tgroup>
3099   </table>
3100
3101  </sect1>
3102
3103
3104  <sect1 id="catalog-pg-opclass">
3105   <title><structname>pg_opclass</structname></title>
3106
3107   <indexterm zone="catalog-pg-opclass">
3108    <primary>pg_opclass</primary>
3109   </indexterm>
3110
3111   <para>
3112    The catalog <structname>pg_opclass</structname> defines
3113    index access method operator classes.  Each operator class defines
3114    semantics for index columns of a particular data type and a particular
3115    index access method.  An operator class essentially specifies that a
3116    particular operator family is applicable to a particular indexable column
3117    data type.  The set of operators from the family that are actually usable
3118    with the indexed column are whichever ones accept the column's data type
3119    as their lefthand input.
3120   </para>
3121
3122   <para>
3123    Operator classes are described at length in <xref linkend="xindex">.
3124   </para>
3125
3126   <table>
3127    <title><structname>pg_opclass</> Columns</title>
3128
3129    <tgroup cols=4>
3130     <thead>
3131      <row>
3132       <entry>Name</entry>
3133       <entry>Type</entry>
3134       <entry>References</entry>
3135       <entry>Description</entry>
3136      </row>
3137     </thead>
3138     <tbody>
3139
3140      <row>
3141       <entry><structfield>opcmethod</structfield></entry>
3142       <entry><type>oid</type></entry>
3143       <entry><literal><link linkend="catalog-pg-am"><structname>pg_am</structname></link>.oid</literal></entry>
3144       <entry>Index access method operator class is for</entry>
3145      </row>
3146
3147      <row>
3148       <entry><structfield>opcname</structfield></entry>
3149       <entry><type>name</type></entry>
3150       <entry></entry>
3151       <entry>Name of this operator class</entry>
3152      </row>
3153
3154      <row>
3155       <entry><structfield>opcnamespace</structfield></entry>
3156       <entry><type>oid</type></entry>
3157       <entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.oid</literal></entry>
3158       <entry>Namespace of this operator class</entry>
3159      </row>
3160
3161      <row>
3162       <entry><structfield>opcowner</structfield></entry>
3163       <entry><type>oid</type></entry>
3164       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
3165       <entry>Owner of the operator class</entry>
3166      </row>
3167
3168      <row>
3169       <entry><structfield>opcfamily</structfield></entry>
3170       <entry><type>oid</type></entry>
3171       <entry><literal><link linkend="catalog-pg-opfamily"><structname>pg_opfamily</structname></link>.oid</literal></entry>
3172       <entry>Operator family containing the operator class</entry>
3173      </row>
3174
3175      <row>
3176       <entry><structfield>opcintype</structfield></entry>
3177       <entry><type>oid</type></entry>
3178       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
3179       <entry>Data type that the operator class indexes</entry>
3180      </row>
3181
3182      <row>
3183       <entry><structfield>opcdefault</structfield></entry>
3184       <entry><type>bool</type></entry>
3185       <entry></entry>
3186       <entry>True if this operator class is the default for <structfield>opcintype</></entry>
3187      </row>
3188
3189      <row>
3190       <entry><structfield>opckeytype</structfield></entry>
3191       <entry><type>oid</type></entry>
3192       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
3193       <entry>Type of data stored in index, or zero if same as <structfield>opcintype</></entry>
3194      </row>
3195
3196     </tbody>
3197    </tgroup>
3198   </table>
3199
3200   <para>
3201    An operator class's <structfield>opcmethod</> must match the
3202    <structname>opfmethod</> of its containing operator family.
3203    Also, there must be no more than one <structname>pg_opclass</structname>
3204    row having <structname>opcdefault</> true for any given combination of
3205    <structname>opcmethod</> and <structname>opcintype</>.
3206   </para>
3207
3208  </sect1>
3209
3210
3211  <sect1 id="catalog-pg-operator">
3212   <title><structname>pg_operator</structname></title>
3213
3214   <indexterm zone="catalog-pg-operator">
3215    <primary>pg_operator</primary>
3216   </indexterm>
3217
3218   <para>
3219    The catalog <structname>pg_operator</> stores information about operators.
3220    See <xref linkend="sql-createoperator" endterm="sql-createoperator-title">
3221    and <xref linkend="xoper"> for more information.
3222   </para>
3223
3224   <table>
3225    <title><structname>pg_operator</> Columns</title>
3226
3227    <tgroup cols=4>
3228     <thead>
3229      <row>
3230       <entry>Name</entry>
3231       <entry>Type</entry>
3232       <entry>References</entry>
3233       <entry>Description</entry>
3234      </row>
3235     </thead>
3236
3237     <tbody>
3238      <row>
3239       <entry><structfield>oprname</structfield></entry>
3240       <entry><type>name</type></entry>
3241       <entry></entry>
3242       <entry>Name of the operator</entry>
3243      </row>
3244
3245      <row>
3246       <entry><structfield>oprnamespace</structfield></entry>
3247       <entry><type>oid</type></entry>
3248       <entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.oid</literal></entry>
3249       <entry>
3250        The OID of the namespace that contains this operator
3251       </entry>
3252      </row>
3253
3254      <row>
3255       <entry><structfield>oprowner</structfield></entry>
3256       <entry><type>oid</type></entry>
3257       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
3258       <entry>Owner of the operator</entry>
3259      </row>
3260
3261      <row>
3262       <entry><structfield>oprkind</structfield></entry>
3263       <entry><type>char</type></entry>
3264       <entry></entry>
3265       <entry>
3266        <literal>b</> = infix (<quote>both</quote>), <literal>l</> = prefix
3267        (<quote>left</quote>), <literal>r</> = postfix (<quote>right</quote>)
3268       </entry>
3269      </row>
3270
3271      <row>
3272       <entry><structfield>oprcanmerge</structfield></entry>
3273       <entry><type>bool</type></entry>
3274       <entry></entry>
3275       <entry>This operator supports merge joins</entry>
3276      </row>
3277
3278      <row>
3279       <entry><structfield>oprcanhash</structfield></entry>
3280       <entry><type>bool</type></entry>
3281       <entry></entry>
3282       <entry>This operator supports hash joins</entry>
3283      </row>
3284
3285      <row>
3286       <entry><structfield>oprleft</structfield></entry>
3287       <entry><type>oid</type></entry>
3288       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
3289       <entry>Type of the left operand</entry>
3290      </row>
3291
3292      <row>
3293       <entry><structfield>oprright</structfield></entry>
3294       <entry><type>oid</type></entry>
3295       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
3296       <entry>Type of the right operand</entry>
3297      </row>
3298
3299      <row>
3300       <entry><structfield>oprresult</structfield></entry>
3301       <entry><type>oid</type></entry>
3302       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
3303       <entry>Type of the result</entry>
3304      </row>
3305
3306      <row>
3307       <entry><structfield>oprcom</structfield></entry>
3308       <entry><type>oid</type></entry>
3309       <entry><literal><link linkend="catalog-pg-operator"><structname>pg_operator</structname></link>.oid</literal></entry>
3310       <entry>Commutator of this operator, if any</entry>
3311      </row>
3312
3313      <row>
3314       <entry><structfield>oprnegate</structfield></entry>
3315       <entry><type>oid</type></entry>
3316       <entry><literal><link linkend="catalog-pg-operator"><structname>pg_operator</structname></link>.oid</literal></entry>
3317       <entry>Negator of this operator, if any</entry>
3318      </row>
3319
3320      <row>
3321       <entry><structfield>oprcode</structfield></entry>
3322       <entry><type>regproc</type></entry>
3323       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
3324       <entry>Function that implements this operator</entry>
3325      </row>
3326
3327      <row>
3328       <entry><structfield>oprrest</structfield></entry>
3329       <entry><type>regproc</type></entry>
3330       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
3331       <entry>Restriction selectivity estimation function for this operator</entry>
3332      </row>
3333
3334      <row>
3335       <entry><structfield>oprjoin</structfield></entry>
3336       <entry><type>regproc</type></entry>
3337       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
3338       <entry>Join selectivity estimation function for this operator</entry>
3339      </row>
3340     </tbody>
3341    </tgroup>
3342   </table>
3343
3344   <para>
3345    Unused column contain zeroes. For example, <structfield>oprleft</structfield>
3346    is zero for a prefix operator.
3347   </para>
3348
3349  </sect1>
3350
3351
3352  <sect1 id="catalog-pg-opfamily">
3353   <title><structname>pg_opfamily</structname></title>
3354
3355   <indexterm zone="catalog-pg-opfamily">
3356    <primary>pg_opfamily</primary>
3357   </indexterm>
3358
3359   <para>
3360    The catalog <structname>pg_opfamily</structname> defines operator families.
3361    Each operator family is a collection of operators and associated
3362    support routines that implement the semantics specified for a particular
3363    index access method.  Furthermore, the operators in a family are all
3364    <quote>compatible</>, in a way that is specified by the access method.
3365    The operator family concept allows cross-data-type operators to be used
3366    with indexes and to be reasoned about using knowledge of access method
3367    semantics.
3368   </para>
3369
3370   <para>
3371    Operator families are described at length in <xref linkend="xindex">.
3372   </para>
3373
3374   <table>
3375    <title><structname>pg_opfamily</> Columns</title>
3376
3377    <tgroup cols=4>
3378     <thead>
3379      <row>
3380       <entry>Name</entry>
3381       <entry>Type</entry>
3382       <entry>References</entry>
3383       <entry>Description</entry>
3384      </row>
3385     </thead>
3386     <tbody>
3387
3388      <row>
3389       <entry><structfield>opfmethod</structfield></entry>
3390       <entry><type>oid</type></entry>
3391       <entry><literal><link linkend="catalog-pg-am"><structname>pg_am</structname></link>.oid</literal></entry>
3392       <entry>Index access method operator family is for</entry>
3393      </row>
3394
3395      <row>
3396       <entry><structfield>opfname</structfield></entry>
3397       <entry><type>name</type></entry>
3398       <entry></entry>
3399       <entry>Name of this operator family</entry>
3400      </row>
3401
3402      <row>
3403       <entry><structfield>opfnamespace</structfield></entry>
3404       <entry><type>oid</type></entry>
3405       <entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.oid</literal></entry>
3406       <entry>Namespace of this operator family</entry>
3407      </row>
3408
3409      <row>
3410       <entry><structfield>opfowner</structfield></entry>
3411       <entry><type>oid</type></entry>
3412       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
3413       <entry>Owner of the operator family</entry>
3414      </row>
3415
3416     </tbody>
3417    </tgroup>
3418   </table>
3419
3420   <para>
3421    The majority of the information defining an operator family is not in its
3422    <structname>pg_opfamily</structname> row, but in the associated rows in
3423    <link linkend="catalog-pg-amop"><structname>pg_amop</structname></link>,
3424    <link linkend="catalog-pg-amproc"><structname>pg_amproc</structname></link>,
3425    and
3426    <link linkend="catalog-pg-opclass"><structname>pg_opclass</structname></link>.
3427   </para>
3428
3429  </sect1>
3430
3431
3432  <sect1 id="catalog-pg-pltemplate">
3433   <title><structname>pg_pltemplate</structname></title>
3434
3435   <indexterm zone="catalog-pg-pltemplate">
3436    <primary>pg_pltemplate</primary>
3437   </indexterm>
3438
3439   <para>
3440    The catalog <structname>pg_pltemplate</structname> stores
3441    <quote>template</> information for procedural languages.
3442    A template for a language allows the language to be created in a
3443    particular database by a simple <command>CREATE LANGUAGE</> command,
3444    with no need to specify implementation details.
3445   </para>
3446
3447   <para>
3448    Unlike most system catalogs, <structname>pg_pltemplate</structname>
3449    is shared across all databases of a cluster: there is only one
3450    copy of <structname>pg_pltemplate</structname> per cluster, not
3451    one per database.  This allows the information to be accessible in
3452    each database as it is needed.
3453   </para>
3454
3455   <table>
3456    <title><structname>pg_pltemplate</> Columns</title>
3457
3458    <tgroup cols=3>
3459     <thead>
3460      <row>
3461       <entry>Name</entry>
3462       <entry>Type</entry>
3463       <entry>Description</entry>
3464      </row>
3465     </thead>
3466
3467     <tbody>
3468      <row>
3469       <entry><structfield>tmplname</structfield></entry>
3470       <entry><type>name</type></entry>
3471       <entry>Name of the language this template is for</entry>
3472      </row>
3473
3474      <row>
3475       <entry><structfield>tmpltrusted</structfield></entry>
3476       <entry><type>boolean</type></entry>
3477       <entry>True if language is considered trusted</entry>
3478      </row>
3479
3480      <row>
3481       <entry><structfield>tmpldbacreate</structfield></entry>
3482       <entry><type>boolean</type></entry>
3483       <entry>True if language may be created by a database owner</entry>
3484      </row>
3485
3486      <row>
3487       <entry><structfield>tmplhandler</structfield></entry>
3488       <entry><type>text</type></entry>
3489       <entry>Name of call handler function</entry>
3490      </row>
3491
3492      <row>
3493       <entry><structfield>tmplvalidator</structfield></entry>
3494       <entry><type>text</type></entry>
3495       <entry>Name of validator function, or NULL if none</entry>
3496      </row>
3497
3498      <row>
3499       <entry><structfield>tmpllibrary</structfield></entry>
3500       <entry><type>text</type></entry>
3501       <entry>Path of shared library that implements language</entry>
3502      </row>
3503
3504      <row>
3505       <entry><structfield>tmplacl</structfield></entry>
3506       <entry><type>aclitem[]</type></entry>
3507       <entry>Access privileges for template (not yet used)</entry>
3508      </row>
3509
3510     </tbody>
3511    </tgroup>
3512   </table>
3513
3514   <para>
3515    There are not currently any commands that manipulate procedural language
3516    templates; to change the built-in information, a superuser must modify
3517    the table using ordinary <command>INSERT</command>, <command>DELETE</command>,
3518    or <command>UPDATE</command> commands.  It is likely that a future
3519    release of <productname>PostgreSQL</productname> will offer
3520    commands to change the entries in a cleaner fashion.
3521   </para>
3522
3523   <para>
3524    When implemented, the <structfield>tmplacl</structfield> field will provide
3525    access control for the template itself (i.e., the right to create a
3526    language using it), not for the languages created from the template.
3527   </para>
3528
3529  </sect1>
3530
3531
3532  <sect1 id="catalog-pg-proc">
3533   <title><structname>pg_proc</structname></title>
3534
3535   <indexterm zone="catalog-pg-proc">
3536    <primary>pg_proc</primary>
3537   </indexterm>
3538
3539   <para>
3540    The catalog <structname>pg_proc</> stores information about functions (or procedures).
3541    See <xref linkend="sql-createfunction" endterm="sql-createfunction-title">
3542    and <xref linkend="xfunc"> for more information.
3543   </para>
3544
3545   <para>
3546    The table contains data for aggregate functions as well as plain functions.
3547    If <structfield>proisagg</structfield> is true, there should be a matching
3548    row in <structfield>pg_aggregate</structfield>.
3549   </para>
3550
3551   <table>
3552    <title><structname>pg_proc</> Columns</title>
3553
3554    <tgroup cols=4>
3555     <thead>
3556      <row>
3557       <entry>Name</entry>
3558       <entry>Type</entry>
3559       <entry>References</entry>
3560       <entry>Description</entry>
3561      </row>
3562     </thead>
3563
3564     <tbody>
3565      <row>
3566       <entry><structfield>proname</structfield></entry>
3567       <entry><type>name</type></entry>
3568       <entry></entry>
3569       <entry>Name of the function</entry>
3570      </row>
3571
3572      <row>
3573       <entry><structfield>pronamespace</structfield></entry>
3574       <entry><type>oid</type></entry>
3575       <entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.oid</literal></entry>
3576       <entry>
3577        The OID of the namespace that contains this function
3578       </entry>
3579      </row>
3580
3581      <row>
3582       <entry><structfield>proowner</structfield></entry>
3583       <entry><type>oid</type></entry>
3584       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
3585       <entry>Owner of the function</entry>
3586      </row>
3587
3588      <row>
3589       <entry><structfield>prolang</structfield></entry>
3590       <entry><type>oid</type></entry>
3591       <entry><literal><link linkend="catalog-pg-language"><structname>pg_language</structname></link>.oid</literal></entry>
3592       <entry>Implementation language or call interface of this function</entry>
3593      </row>
3594
3595      <row>
3596       <entry><structfield>procost</structfield></entry>
3597       <entry><type>float4</type></entry>
3598       <entry></entry>
3599       <entry>Estimated execution cost (in units of
3600        <xref linkend="guc-cpu-operator-cost">); if <structfield>proretset</>,
3601        this is cost per row returned</entry>
3602      </row>
3603
3604      <row>
3605       <entry><structfield>prorows</structfield></entry>
3606       <entry><type>float4</type></entry>
3607       <entry></entry>
3608       <entry>Estimated number of result rows (zero if not <structfield>proretset</>)</entry>
3609      </row>
3610
3611      <row>
3612       <entry><structfield>provariadic</structfield></entry>
3613       <entry><type>oid</type></entry>
3614       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
3615       <entry>Data type of the variadic array parameter's elements,
3616        or zero if the function does not have a variadic parameter</entry>
3617      </row>
3618
3619      <row>
3620       <entry><structfield>proisagg</structfield></entry>
3621       <entry><type>bool</type></entry>
3622       <entry></entry>
3623       <entry>Function is an aggregate function</entry>
3624      </row>
3625
3626      <row>
3627       <entry><structfield>prosecdef</structfield></entry>
3628       <entry><type>bool</type></entry>
3629       <entry></entry>
3630       <entry>Function is a security definer (i.e., a <quote>setuid</>
3631       function)</entry>
3632      </row>
3633
3634      <row>
3635       <entry><structfield>proisstrict</structfield></entry>
3636       <entry><type>bool</type></entry>
3637       <entry></entry>
3638       <entry>
3639        Function returns null if any call argument is null.  In that
3640        case the function won't actually be called at all.  Functions
3641        that are not <quote>strict</quote> must be prepared to handle
3642        null inputs
3643       </entry>
3644      </row>
3645
3646      <row>
3647       <entry><structfield>proretset</structfield></entry>
3648       <entry><type>bool</type></entry>
3649       <entry></entry>
3650       <entry>Function returns a set (i.e., multiple values of the specified
3651       data type)</entry>
3652      </row>
3653
3654      <row>
3655       <entry><structfield>provolatile</structfield></entry>
3656       <entry><type>char</type></entry>
3657       <entry></entry>
3658       <entry>
3659        <structfield>provolatile</structfield> tells whether the function's
3660        result depends only on its input arguments, or is affected by outside
3661        factors.
3662        It is <literal>i</literal> for <quote>immutable</> functions,
3663        which always deliver the same result for the same inputs.
3664        It is <literal>s</literal> for <quote>stable</> functions,
3665        whose results (for fixed inputs) do not change within a scan.
3666        It is <literal>v</literal> for <quote>volatile</> functions,
3667        whose results might change at any time.  (Use <literal>v</literal> also
3668        for functions with side-effects, so that calls to them cannot get
3669        optimized away.)
3670       </entry>
3671      </row>
3672
3673      <row>
3674       <entry><structfield>pronargs</structfield></entry>
3675       <entry><type>int2</type></entry>
3676       <entry></entry>
3677       <entry>Number of arguments</entry>
3678      </row>
3679
3680      <row>
3681       <entry><structfield>prorettype</structfield></entry>
3682       <entry><type>oid</type></entry>
3683       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
3684       <entry>Data type of the return value</entry>
3685      </row>
3686
3687      <row>
3688       <entry><structfield>proargtypes</structfield></entry>
3689       <entry><type>oidvector</type></entry>
3690       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
3691       <entry>
3692        An array with the data types of the function arguments.  This includes
3693        only input arguments (including <literal>INOUT</literal> and
3694        <literal>VARIADIC</> arguments), and thus represents
3695        the call signature of the function
3696       </entry>
3697      </row>
3698
3699      <row>
3700       <entry><structfield>proallargtypes</structfield></entry>
3701       <entry><type>oid[]</type></entry>
3702       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
3703       <entry>
3704        An array with the data types of the function arguments.  This includes
3705        all arguments (including <literal>OUT</literal> and
3706        <literal>INOUT</literal> arguments); however, if all the
3707        arguments are <literal>IN</literal> arguments, this field will be null.
3708        Note that subscripting is 1-based, whereas for historical reasons
3709        <structfield>proargtypes</> is subscripted from 0
3710       </entry>
3711      </row>
3712
3713      <row>
3714       <entry><structfield>proargmodes</structfield></entry>
3715       <entry><type>char[]</type></entry>
3716       <entry></entry>
3717       <entry>
3718         An array with the modes of the function arguments, encoded as
3719         <literal>i</literal> for <literal>IN</> arguments,
3720         <literal>o</literal> for <literal>OUT</> arguments,
3721         <literal>b</literal> for <literal>INOUT</> arguments,
3722         <literal>v</literal> for <literal>VARIADIC</> arguments,
3723         <literal>t</literal> for <literal>TABLE</> arguments.
3724         If all the arguments are <literal>IN</literal> arguments,
3725         this field will be null.
3726         Note that subscripts correspond to positions of
3727         <structfield>proallargtypes</> not <structfield>proargtypes</>
3728       </entry>
3729      </row>
3730
3731      <row>
3732       <entry><structfield>proargnames</structfield></entry>
3733       <entry><type>text[]</type></entry>
3734       <entry></entry>
3735       <entry>
3736         An array with the names of the function arguments.
3737         Arguments without a name are set to empty strings in the array.
3738         If none of the arguments have a name, this field will be null.
3739         Note that subscripts correspond to positions of
3740         <structfield>proallargtypes</> not <structfield>proargtypes</>
3741       </entry>
3742      </row>
3743
3744      <row>
3745       <entry><structfield>prosrc</structfield></entry>
3746       <entry><type>text</type></entry>
3747       <entry></entry>
3748       <entry>
3749        This tells the function handler how to invoke the function.  It
3750        might be the actual source code of the function for interpreted
3751        languages, a link symbol, a file name, or just about anything
3752        else, depending on the implementation language/call convention
3753       </entry>
3754      </row>
3755
3756      <row>
3757       <entry><structfield>probin</structfield></entry>
3758       <entry><type>bytea</type></entry>
3759       <entry></entry>
3760       <entry>
3761        Additional information about how to invoke the function.
3762        Again, the interpretation is language-specific
3763       </entry>
3764      </row>
3765
3766      <row>
3767       <entry><structfield>proconfig</structfield></entry>
3768       <entry><type>text[]</type></entry>
3769       <entry></entry>
3770       <entry>Function's local settings for run-time configuration variables</entry>
3771      </row>
3772
3773      <row>
3774       <entry><structfield>proacl</structfield></entry>
3775       <entry><type>aclitem[]</type></entry>
3776       <entry></entry>
3777       <entry>
3778        Access privileges; see
3779        <xref linkend="sql-grant" endterm="sql-grant-title"> and
3780        <xref linkend="sql-revoke" endterm="sql-revoke-title">
3781        for details
3782       </entry>
3783      </row>
3784     </tbody>
3785    </tgroup>
3786   </table>
3787
3788   <para>
3789    For compiled functions, both built-in and dynamically loaded,
3790    <structfield>prosrc</structfield> contains the function's C-language
3791    name (link symbol).  For all other currently-known language types,
3792    <structfield>prosrc</structfield> contains the function's source
3793    text.  <structfield>probin</structfield> is unused except for
3794    dynamically-loaded C functions, for which it gives the name of the
3795    shared library file containing the function.
3796   </para>
3797
3798  </sect1>
3799
3800  <sect1 id="catalog-pg-rewrite">
3801   <title><structname>pg_rewrite</structname></title>
3802
3803   <indexterm zone="catalog-pg-rewrite">
3804    <primary>pg_rewrite</primary>
3805   </indexterm>
3806
3807   <para>
3808    The catalog <structname>pg_rewrite</structname> stores rewrite rules for tables and views.
3809   </para>
3810
3811   <table>
3812    <title><structname>pg_rewrite</> Columns</title>
3813
3814    <tgroup cols=4>
3815     <thead>
3816      <row>
3817       <entry>Name</entry>
3818       <entry>Type</entry>
3819       <entry>References</entry>
3820       <entry>Description</entry>
3821      </row>
3822     </thead>
3823
3824     <tbody>
3825      <row>
3826       <entry><structfield>rulename</structfield></entry>
3827       <entry><type>name</type></entry>
3828       <entry></entry>
3829       <entry>Rule name</entry>
3830      </row>
3831
3832      <row>
3833       <entry><structfield>ev_class</structfield></entry>
3834       <entry><type>oid</type></entry>
3835       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
3836       <entry>The table this rule is for</entry>
3837      </row>
3838
3839      <row>
3840       <entry><structfield>ev_attr</structfield></entry>
3841       <entry><type>int2</type></entry>
3842       <entry></entry>
3843       <entry>The column this rule is for (currently, always zero to
3844       indicate the whole table)</entry>
3845      </row>
3846
3847      <row>
3848       <entry><structfield>ev_type</structfield></entry>
3849       <entry><type>char</type></entry>
3850       <entry></entry>
3851       <entry>
3852        Event type that the rule is for: 1 = <command>SELECT</>, 2 =
3853        <command>UPDATE</>, 3 = <command>INSERT</>, 4 =
3854        <command>DELETE</>
3855       </entry>
3856      </row>
3857
3858      <row>
3859       <entry><structfield>ev_enabled</structfield></entry>
3860       <entry><type>char</type></entry>
3861       <entry></entry>
3862       <entry>
3863        Controls in which <xref linkend="guc-session-replication-role"> modes
3864        the rule fires.
3865        <literal>O</> = rule fires in <quote>origin</> and <quote>local</> modes,
3866        <literal>D</> = rule is disabled,
3867        <literal>R</> = rule fires in <quote>replica</> mode,
3868        <literal>A</> = rule fires always.
3869       </entry>
3870      </row>
3871
3872      <row>
3873       <entry><structfield>is_instead</structfield></entry>
3874       <entry><type>bool</type></entry>
3875       <entry></entry>
3876       <entry>True if the rule is an <literal>INSTEAD</literal> rule</entry>
3877      </row>
3878
3879      <row>
3880       <entry><structfield>ev_qual</structfield></entry>
3881       <entry><type>text</type></entry>
3882       <entry></entry>
3883       <entry>
3884        Expression tree (in the form of a
3885        <function>nodeToString()</function> representation) for the
3886        rule's qualifying condition
3887       </entry>
3888      </row>
3889
3890      <row>
3891       <entry><structfield>ev_action</structfield></entry>
3892       <entry><type>text</type></entry>
3893       <entry></entry>
3894       <entry>
3895        Query tree (in the form of a
3896        <function>nodeToString()</function> representation) for the
3897        rule's action
3898       </entry>
3899      </row>
3900     </tbody>
3901    </tgroup>
3902   </table>
3903
3904   <note>
3905    <para>
3906     <literal>pg_class.relhasrules</literal>
3907     must be true if a table has any rules in this catalog.
3908    </para>
3909   </note>
3910
3911  </sect1>
3912
3913
3914  <sect1 id="catalog-pg-shdepend">
3915   <title><structname>pg_shdepend</structname></title>
3916
3917   <indexterm zone="catalog-pg-shdepend">
3918    <primary>pg_shdepend</primary>
3919   </indexterm>
3920
3921   <para>
3922    The catalog <structname>pg_shdepend</structname> records the
3923    dependency relationships between database objects and shared objects,
3924    such as roles.  This information allows
3925    <productname>PostgreSQL</productname> to ensure that those objects are
3926    unreferenced before attempting to delete them.
3927   </para>
3928
3929   <para>
3930    See also <link linkend="catalog-pg-depend"><structname>pg_depend</structname></link>,
3931    which performs a similar function for dependencies involving objects
3932    within a single database.
3933   </para>
3934
3935   <para>
3936    Unlike most system catalogs, <structname>pg_shdepend</structname>
3937    is shared across all databases of a cluster: there is only one
3938    copy of <structname>pg_shdepend</structname> per cluster, not
3939    one per database.
3940   </para>
3941
3942   <table>
3943    <title><structname>pg_shdepend</> Columns</title>
3944
3945    <tgroup cols=4>
3946     <thead>
3947      <row>
3948       <entry>Name</entry>
3949       <entry>Type</entry>
3950       <entry>References</entry>
3951       <entry>Description</entry>
3952      </row>
3953     </thead>
3954
3955     <tbody>
3956      <row>
3957       <entry><structfield>dbid</structfield></entry>
3958       <entry><type>oid</type></entry>
3959       <entry><literal><link linkend="catalog-pg-database"><structname>pg_database</structname></link>.oid</literal></entry>
3960       <entry>The OID of the database the dependent object is in,
3961        or zero for a shared object</entry>
3962      </row>
3963
3964      <row>
3965       <entry><structfield>classid</structfield></entry>
3966       <entry><type>oid</type></entry>
3967       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
3968       <entry>The OID of the system catalog the dependent object is in</entry>
3969      </row>
3970
3971      <row>
3972       <entry><structfield>objid</structfield></entry>
3973       <entry><type>oid</type></entry>
3974       <entry>any OID column</entry>
3975       <entry>The OID of the specific dependent object</entry>
3976      </row>
3977
3978      <row>
3979       <entry><structfield>refclassid</structfield></entry>
3980       <entry><type>oid</type></entry>
3981       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
3982       <entry>The OID of the system catalog the referenced object is in
3983        (must be a shared catalog)</entry>
3984      </row>
3985
3986      <row>
3987       <entry><structfield>refobjid</structfield></entry>
3988       <entry><type>oid</type></entry>
3989       <entry>any OID column</entry>
3990       <entry>The OID of the specific referenced object</entry>
3991      </row>
3992
3993      <row>
3994       <entry><structfield>deptype</structfield></entry>
3995       <entry><type>char</type></entry>
3996       <entry></entry>
3997       <entry>
3998        A code defining the specific semantics of this dependency relationship; see text
3999       </entry>
4000      </row>
4001
4002     </tbody>
4003    </tgroup>
4004   </table>
4005
4006   <para>
4007    In all cases, a <structname>pg_shdepend</structname> entry indicates that
4008    the referenced object cannot be dropped without also dropping the dependent
4009    object.  However, there are several subflavors identified by
4010    <structfield>deptype</>:
4011
4012    <variablelist>
4013     <varlistentry>
4014      <term><symbol>SHARED_DEPENDENCY_OWNER</> (<literal>o</>)</term>
4015      <listitem>
4016       <para>
4017        The referenced object (which must be a role) is the owner of the
4018        dependent object.
4019       </para>
4020      </listitem>
4021     </varlistentry>
4022
4023     <varlistentry>
4024      <term><symbol>SHARED_DEPENDENCY_ACL</> (<literal>a</>)</term>
4025      <listitem>
4026       <para>
4027        The referenced object (which must be a role) is mentioned in the
4028        ACL (access control list, i.e., privileges list) of the
4029        dependent object.  (A <symbol>SHARED_DEPENDENCY_ACL</> entry is
4030        not made for the owner of the object, since the owner will have
4031        a <symbol>SHARED_DEPENDENCY_OWNER</> entry anyway.)
4032       </para>
4033      </listitem>
4034     </varlistentry>
4035
4036     <varlistentry>
4037      <term><symbol>SHARED_DEPENDENCY_PIN</> (<literal>p</>)</term>
4038      <listitem>
4039       <para>
4040        There is no dependent object; this type of entry is a signal
4041        that the system itself depends on the referenced object, and so
4042        that object must never be deleted.  Entries of this type are
4043        created only by <command>initdb</command>.  The columns for the
4044        dependent object contain zeroes.
4045       </para>
4046      </listitem>
4047     </varlistentry>
4048    </variablelist>
4049
4050    Other dependency flavors might be needed in future.  Note in particular
4051    that the current definition only supports roles as referenced objects.
4052   </para>
4053
4054  </sect1>
4055
4056  <sect1 id="catalog-pg-shdescription">
4057   <title><structname>pg_shdescription</structname></title>
4058
4059   <indexterm zone="catalog-pg-shdescription">
4060    <primary>pg_shdescription</primary>
4061   </indexterm>
4062
4063   <para>
4064    The catalog <structname>pg_shdescription</structname> stores optional
4065    descriptions (comments) for shared database objects.  Descriptions can be
4066    manipulated with the <xref linkend="sql-comment"
4067    endterm="sql-comment-title"> command and viewed with
4068    <application>psql</application>'s <literal>\d</literal> commands.
4069   </para>
4070
4071   <para>
4072    See also <link linkend="catalog-pg-description"><structname>pg_description</structname></link>,
4073    which performs a similar function for descriptions involving objects
4074    within a single database.
4075   </para>
4076
4077   <para>
4078    Unlike most system catalogs, <structname>pg_shdescription</structname>
4079    is shared across all databases of a cluster: there is only one
4080    copy of <structname>pg_shdescription</structname> per cluster, not
4081    one per database.
4082   </para>
4083
4084   <table>
4085    <title><structname>pg_shdescription</> Columns</title>
4086
4087    <tgroup cols=4>
4088     <thead>
4089      <row>
4090       <entry>Name</entry>
4091       <entry>Type</entry>
4092       <entry>References</entry>
4093       <entry>Description</entry>
4094      </row>
4095     </thead>
4096
4097     <tbody>
4098      <row>
4099       <entry><structfield>objoid</structfield></entry>
4100       <entry><type>oid</type></entry>
4101       <entry>any OID column</entry>
4102       <entry>The OID of the object this description pertains to</entry>
4103      </row>
4104
4105      <row>
4106       <entry><structfield>classoid</structfield></entry>
4107       <entry><type>oid</type></entry>
4108       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
4109       <entry>The OID of the system catalog this object appears in</entry>
4110      </row>
4111
4112      <row>
4113       <entry><structfield>description</structfield></entry>
4114       <entry><type>text</type></entry>
4115       <entry></entry>
4116       <entry>Arbitrary text that serves as the description of this object</entry>
4117      </row>
4118     </tbody>
4119    </tgroup>
4120   </table>
4121
4122  </sect1>
4123
4124
4125  <sect1 id="catalog-pg-statistic">
4126   <title><structname>pg_statistic</structname></title>
4127
4128   <indexterm zone="catalog-pg-statistic">
4129    <primary>pg_statistic</primary>
4130   </indexterm>
4131
4132   <para>
4133    The catalog <structname>pg_statistic</structname> stores
4134    statistical data about the contents of the database.  Entries are
4135    created by <xref linkend="sql-analyze" endterm="sql-analyze-title">
4136    and subsequently used by the query planner.  There is one entry for
4137    each table column that has been analyzed.  Note that all the
4138    statistical data is inherently approximate, even assuming that it
4139    is up-to-date.
4140   </para>
4141
4142   <para>
4143    <structname>pg_statistic</structname> also stores statistical data about
4144    the values of index expressions.  These are described as if they were
4145    actual data columns; in particular, <structfield>starelid</structfield>
4146    references the index.  No entry is made for an ordinary non-expression
4147    index column, however, since it would be redundant with the entry
4148    for the underlying table column.
4149   </para>
4150
4151   <para>
4152    Since different kinds of statistics might be appropriate for different
4153    kinds of data, <structname>pg_statistic</structname> is designed not
4154    to assume very much about what sort of statistics it stores.  Only
4155    extremely general statistics (such as nullness) are given dedicated
4156    columns in <structname>pg_statistic</structname>.  Everything else
4157    is stored in <quote>slots</quote>, which are groups of associated columns
4158    whose content is identified by a code number in one of the slot's columns.
4159    For more information see
4160    <filename>src/include/catalog/pg_statistic.h</filename>.
4161   </para>
4162
4163   <para>
4164    <structname>pg_statistic</structname> should not be readable by the
4165    public, since even statistical information about a table's contents
4166    might be considered sensitive.  (Example: minimum and maximum values
4167    of a salary column might be quite interesting.)
4168    <link linkend="view-pg-stats"><structname>pg_stats</structname></link>
4169    is a publicly readable view on
4170    <structname>pg_statistic</structname> that only exposes information
4171    about those tables that are readable by the current user.
4172   </para>
4173
4174   <table>
4175    <title><structname>pg_statistic</> Columns</title>
4176
4177    <tgroup cols=4>
4178     <thead>
4179      <row>
4180       <entry>Name</entry>
4181       <entry>Type</entry>
4182       <entry>References</entry>
4183       <entry>Description</entry>
4184      </row>
4185     </thead>
4186
4187     <tbody>
4188      <row>
4189       <entry><structfield>starelid</structfield></entry>
4190       <entry><type>oid</type></entry>
4191       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
4192       <entry>The table or index that the described column belongs to</entry>
4193      </row>
4194
4195      <row>
4196       <entry><structfield>staattnum</structfield></entry>
4197       <entry><type>int2</type></entry>
4198       <entry><literal><link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link>.attnum</literal></entry>
4199       <entry>The number of the described column</entry>
4200      </row>
4201
4202      <row>
4203       <entry><structfield>stanullfrac</structfield></entry>
4204       <entry><type>float4</type></entry>
4205       <entry></entry>
4206       <entry>The fraction of the column's entries that are null</entry>
4207      </row>
4208
4209      <row>
4210       <entry><structfield>stawidth</structfield></entry>
4211       <entry><type>int4</type></entry>
4212       <entry></entry>
4213       <entry>The average stored width, in bytes, of nonnull entries</entry>
4214      </row>
4215
4216      <row>
4217       <entry><structfield>stadistinct</structfield></entry>
4218       <entry><type>float4</type></entry>
4219       <entry></entry>
4220       <entry>The number of distinct nonnull data values in the column.
4221       A value greater than zero is the actual number of distinct values.
4222       A value less than zero is the negative of a fraction of the number
4223       of rows in the table (for example, a column in which values appear about
4224       twice on the average could be represented by <structfield>stadistinct</> = -0.5).
4225       A zero value means the number of distinct values is unknown
4226       </entry>
4227      </row>
4228
4229      <row>
4230       <entry><structfield>stakind<replaceable>N</></structfield></entry>
4231       <entry><type>int2</type></entry>
4232       <entry></entry>
4233       <entry>
4234        A code number indicating the kind of statistics stored in the
4235        <replaceable>N</>th <quote>slot</quote> of the
4236        <structname>pg_statistic</structname> row
4237       </entry>
4238      </row>
4239
4240      <row>
4241       <entry><structfield>staop<replaceable>N</></structfield></entry>
4242       <entry><type>oid</type></entry>
4243       <entry><literal><link linkend="catalog-pg-operator"><structname>pg_operator</structname></link>.oid</literal></entry>
4244       <entry>
4245        An operator used to derive the statistics stored in the
4246        <replaceable>N</>th <quote>slot</quote>.  For example, a
4247        histogram slot would show the <literal>&lt;</literal> operator
4248        that defines the sort order of the data
4249       </entry>
4250      </row>
4251
4252      <row>
4253       <entry><structfield>stanumbers<replaceable>N</></structfield></entry>
4254       <entry><type>float4[]</type></entry>
4255       <entry></entry>
4256       <entry>
4257        Numerical statistics of the appropriate kind for the
4258        <replaceable>N</>th <quote>slot</quote>, or NULL if the slot
4259        kind does not involve numerical values
4260       </entry>
4261      </row>
4262
4263      <row>
4264       <entry><structfield>stavalues<replaceable>N</></structfield></entry>
4265       <entry><type>anyarray</type></entry>
4266       <entry></entry>
4267       <entry>
4268        Column data values of the appropriate kind for the
4269        <replaceable>N</>th <quote>slot</quote>, or NULL if the slot
4270        kind does not store any data values.  Each array's element
4271        values are actually of the specific column's data type, so there
4272        is no way to define these columns' type more specifically than
4273        <type>anyarray</>
4274       </entry>
4275      </row>
4276     </tbody>
4277    </tgroup>
4278   </table>
4279
4280  </sect1>
4281
4282
4283  <sect1 id="catalog-pg-tablespace">
4284   <title><structname>pg_tablespace</structname></title>
4285
4286   <indexterm zone="catalog-pg-tablespace">
4287    <primary>pg_tablespace</primary>
4288   </indexterm>
4289
4290   <para>
4291    The catalog <structname>pg_tablespace</structname> stores information
4292    about the available tablespaces.  Tables can be placed in particular
4293    tablespaces to aid administration of disk layout.
4294   </para>
4295
4296   <para>
4297    Unlike most system catalogs, <structname>pg_tablespace</structname>
4298    is shared across all databases of a cluster: there is only one
4299    copy of <structname>pg_tablespace</structname> per cluster, not
4300    one per database.
4301   </para>
4302
4303   <table>
4304    <title><structname>pg_tablespace</> Columns</title>
4305
4306    <tgroup cols=4>
4307     <thead>
4308      <row>
4309       <entry>Name</entry>
4310       <entry>Type</entry>
4311       <entry>References</entry>
4312       <entry>Description</entry>
4313      </row>
4314     </thead>
4315
4316     <tbody>
4317      <row>
4318       <entry><structfield>spcname</structfield></entry>
4319       <entry><type>name</type></entry>
4320       <entry></entry>
4321       <entry>Tablespace name</entry>
4322      </row>
4323
4324      <row>
4325       <entry><structfield>spcowner</structfield></entry>
4326       <entry><type>oid</type></entry>
4327       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
4328       <entry>Owner of the tablespace, usually the user who created it</entry>
4329      </row>
4330
4331      <row>
4332       <entry><structfield>spclocation</structfield></entry>
4333       <entry><type>text</type></entry>
4334       <entry></entry>
4335       <entry>Location (directory path) of the tablespace</entry>
4336      </row>
4337
4338      <row>
4339       <entry><structfield>spcacl</structfield></entry>
4340       <entry><type>aclitem[]</type></entry>
4341       <entry></entry>
4342       <entry>
4343        Access privileges; see
4344        <xref linkend="sql-grant" endterm="sql-grant-title"> and
4345        <xref linkend="sql-revoke" endterm="sql-revoke-title">
4346        for details
4347       </entry>
4348      </row>
4349     </tbody>
4350    </tgroup>
4351   </table>
4352  </sect1>
4353
4354
4355  <sect1 id="catalog-pg-trigger">
4356   <title><structname>pg_trigger</structname></title>
4357
4358   <indexterm zone="catalog-pg-trigger">
4359    <primary>pg_trigger</primary>
4360   </indexterm>
4361
4362   <para>
4363    The catalog <structname>pg_trigger</structname> stores triggers on tables.
4364    See <xref linkend="sql-createtrigger" endterm="sql-createtrigger-title">
4365    for more information.
4366   </para>
4367
4368   <table>
4369    <title><structname>pg_trigger</> Columns</title>
4370
4371    <tgroup cols=4>
4372     <thead>
4373      <row>
4374       <entry>Name</entry>
4375       <entry>Type</entry>
4376       <entry>References</entry>
4377       <entry>Description</entry>
4378      </row>
4379     </thead>
4380
4381     <tbody>
4382      <row>
4383       <entry><structfield>tgrelid</structfield></entry>
4384       <entry><type>oid</type></entry>
4385       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
4386       <entry>The table this trigger is on</entry>
4387      </row>
4388
4389      <row>
4390       <entry><structfield>tgname</structfield></entry>
4391       <entry><type>name</type></entry>
4392       <entry></entry>
4393       <entry>Trigger name (must be unique among triggers of same table)</entry>
4394      </row>
4395
4396      <row>
4397       <entry><structfield>tgfoid</structfield></entry>
4398       <entry><type>oid</type></entry>
4399       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
4400       <entry>The function to be called</entry>
4401      </row>
4402
4403      <row>
4404       <entry><structfield>tgtype</structfield></entry>
4405       <entry><type>int2</type></entry>
4406       <entry></entry>
4407       <entry>Bit mask identifying trigger conditions</entry>
4408      </row>
4409
4410      <row>
4411       <entry><structfield>tgenabled</structfield></entry>
4412       <entry><type>char</type></entry>
4413       <entry></entry>
4414       <entry>
4415        Controls in which <xref linkend="guc-session-replication-role"> modes
4416        the trigger fires.
4417        <literal>O</> = trigger fires in <quote>origin</> and <quote>local</> modes,
4418        <literal>D</> = trigger is disabled,
4419        <literal>R</> = trigger fires in <quote>replica</> mode,
4420        <literal>A</> = trigger fires always.
4421       </entry>
4422      </row>
4423
4424      <row>
4425       <entry><structfield>tgisconstraint</structfield></entry>
4426       <entry><type>bool</type></entry>
4427       <entry></entry>
4428       <entry>True if trigger is a <quote>constraint trigger</></entry>
4429      </row>
4430
4431      <row>
4432       <entry><structfield>tgconstrname</structfield></entry>
4433       <entry><type>name</type></entry>
4434       <entry></entry>
4435       <entry>Constraint name, if a constraint trigger</entry>
4436      </row>
4437
4438      <row>
4439       <entry><structfield>tgconstrrelid</structfield></entry>
4440       <entry><type>oid</type></entry>
4441       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
4442       <entry>The table referenced by a referential integrity constraint</entry>
4443      </row>
4444
4445      <row>
4446       <entry><structfield>tgconstraint</structfield></entry>
4447       <entry><type>oid</type></entry>
4448       <entry><literal><link linkend="catalog-pg-constraint"><structname>pg_constraint</structname></link>.oid</literal></entry>
4449       <entry>The <structname>pg_constraint</> entry owning the trigger, if any</entry>
4450      </row>
4451
4452      <row>
4453       <entry><structfield>tgdeferrable</structfield></entry>
4454       <entry><type>bool</type></entry>
4455       <entry></entry>
4456       <entry>True if constraint trigger is deferrable</entry>
4457      </row>
4458
4459      <row>
4460       <entry><structfield>tginitdeferred</structfield></entry>
4461       <entry><type>bool</type></entry>
4462       <entry></entry>
4463       <entry>True if constraint trigger is initially deferred</entry>
4464      </row>
4465
4466      <row>
4467       <entry><structfield>tgnargs</structfield></entry>
4468       <entry><type>int2</type></entry>
4469       <entry></entry>
4470       <entry>Number of argument strings passed to trigger function</entry>
4471      </row>
4472
4473      <row>
4474       <entry><structfield>tgattr</structfield></entry>
4475       <entry><type>int2vector</type></entry>
4476       <entry></entry>
4477       <entry>Currently unused</entry>
4478      </row>
4479
4480      <row>
4481       <entry><structfield>tgargs</structfield></entry>
4482       <entry><type>bytea</type></entry>
4483       <entry></entry>
4484       <entry>Argument strings to pass to trigger, each NULL-terminated</entry>
4485      </row>
4486     </tbody>
4487    </tgroup>
4488   </table>
4489
4490   <note>
4491    <para>
4492     When <structfield>tgconstraint</> is nonzero,
4493     <structfield>tgisconstraint</> must be true, and
4494     <structfield>tgconstrname</>, <structfield>tgconstrrelid</>,
4495     <structfield>tgdeferrable</>, <structfield>tginitdeferred</> are redundant
4496     with the referenced <structname>pg_constraint</> entry.  The reason we
4497     keep these fields is that we support <quote>stand-alone</> constraint
4498     triggers with no corresponding <structname>pg_constraint</> entry.
4499    </para>
4500   </note>
4501
4502   <note>
4503    <para>
4504     <literal>pg_class.reltriggers</literal> needs to agree with the
4505     number of triggers found in this table for each relation.
4506    </para>
4507   </note>
4508
4509  </sect1>
4510
4511
4512  <sect1 id="catalog-pg-ts-config">
4513   <title><structname>pg_ts_config</structname></title>
4514
4515   <indexterm zone="catalog-pg-ts-config">
4516    <primary>pg_ts_config</primary>
4517   </indexterm>
4518
4519   <para>
4520    The <structname>pg_ts_config</structname> catalog contains entries
4521    representing text search configurations.  A configuration specifies
4522    a particular text search parser and a list of dictionaries to use
4523    for each of the parser's output token types.  The parser is shown
4524    in the <structname>pg_ts_config</structname> entry, but the
4525    token-to-dictionary mapping is defined by subsidiary entries in <link
4526    linkend="catalog-pg-ts-config-map"><structname>pg_ts_config_map</structname></link>.
4527   </para>
4528
4529   <para>
4530    <productname>PostgreSQL</productname>'s text search features are
4531    described at length in <xref linkend="textsearch">.
4532   </para>
4533
4534   <table>
4535    <title><structname>pg_ts_config</> Columns</title>
4536
4537    <tgroup cols=4>
4538     <thead>
4539      <row>
4540       <entry>Name</entry>
4541       <entry>Type</entry>
4542       <entry>References</entry>
4543       <entry>Description</entry>
4544      </row>
4545     </thead>
4546
4547     <tbody>
4548      <row>
4549       <entry><structfield>cfgname</structfield></entry>
4550       <entry><type>name</type></entry>
4551       <entry></entry>
4552       <entry>Text search configuration name</entry>
4553      </row>
4554
4555      <row>
4556       <entry><structfield>cfgnamespace</structfield></entry>
4557       <entry><type>oid</type></entry>
4558       <entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.oid</literal></entry>
4559       <entry>
4560        The OID of the namespace that contains this configuration
4561       </entry>
4562      </row>
4563
4564      <row>
4565       <entry><structfield>cfgowner</structfield></entry>
4566       <entry><type>oid</type></entry>
4567       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
4568       <entry>Owner of the configuration</entry>
4569      </row>
4570
4571      <row>
4572       <entry><structfield>cfgparser</structfield></entry>
4573       <entry><type>oid</type></entry>
4574       <entry><literal><link linkend="catalog-pg-ts-parser"><structname>pg_ts_parser</structname></link>.oid</literal></entry>
4575       <entry>The OID of the text search parser for this configuration</entry>
4576      </row>
4577     </tbody>
4578    </tgroup>
4579   </table>
4580  </sect1>
4581
4582
4583  <sect1 id="catalog-pg-ts-config-map">
4584   <title><structname>pg_ts_config_map</structname></title>
4585
4586   <indexterm zone="catalog-pg-ts-config-map">
4587    <primary>pg_ts_config_map</primary>
4588   </indexterm>
4589
4590   <para>
4591    The <structname>pg_ts_config_map</structname> catalog contains entries
4592    showing which text search dictionaries should be consulted, and in
4593    what order, for each output token type of each text search configuration's
4594    parser.
4595   </para>
4596
4597   <para>
4598    <productname>PostgreSQL</productname>'s text search features are
4599    described at length in <xref linkend="textsearch">.
4600   </para>
4601
4602   <table>
4603    <title><structname>pg_ts_config_map</> Columns</title>
4604
4605    <tgroup cols=4>
4606     <thead>
4607      <row>
4608       <entry>Name</entry>
4609       <entry>Type</entry>
4610       <entry>References</entry>
4611       <entry>Description</entry>
4612      </row>
4613     </thead>
4614
4615     <tbody>
4616      <row>
4617       <entry><structfield>mapcfg</structfield></entry>
4618       <entry><type>oid</type></entry>
4619       <entry><literal><link linkend="catalog-pg-ts-config"><structname>pg_ts_config</structname></link>.oid</literal></entry>
4620       <entry>The OID of the <structname>pg_ts_config</> entry owning this map entry</entry>
4621      </row>
4622
4623      <row>
4624       <entry><structfield>maptokentype</structfield></entry>
4625       <entry><type>integer</type></entry>
4626       <entry></entry>
4627       <entry>A token type emitted by the configuration's parser</entry>
4628      </row>
4629
4630      <row>
4631       <entry><structfield>mapseqno</structfield></entry>
4632       <entry><type>integer</type></entry>
4633       <entry></entry>
4634       <entry>Order in which to consult this entry (lower
4635        <structfield>mapseqno</>s first)</entry>
4636      </row>
4637
4638      <row>
4639       <entry><structfield>mapdict</structfield></entry>
4640       <entry><type>oid</type></entry>
4641       <entry><literal><link linkend="catalog-pg-ts-dict"><structname>pg_ts_dict</structname></link>.oid</literal></entry>
4642       <entry>The OID of the text search dictionary to consult</entry>
4643      </row>
4644     </tbody>
4645    </tgroup>
4646   </table>
4647  </sect1>
4648
4649
4650  <sect1 id="catalog-pg-ts-dict">
4651   <title><structname>pg_ts_dict</structname></title>
4652
4653   <indexterm zone="catalog-pg-ts-dict">
4654    <primary>pg_ts_dict</primary>
4655   </indexterm>
4656
4657   <para>
4658    The <structname>pg_ts_dict</structname> catalog contains entries
4659    defining text search dictionaries.  A dictionary depends on a text
4660    search template, which specifies all the implementation functions
4661    needed; the dictionary itself provides values for the user-settable
4662    parameters supported by the template.  This division of labor allows
4663    dictionaries to be created by unprivileged users.  The parameters
4664    are specified by a text string <structfield>dictinitoption</>,
4665    whose format and meaning vary depending on the template.
4666   </para>
4667
4668   <para>
4669    <productname>PostgreSQL</productname>'s text search features are
4670    described at length in <xref linkend="textsearch">.
4671   </para>
4672
4673   <table>
4674    <title><structname>pg_ts_dict</> Columns</title>
4675
4676    <tgroup cols=4>
4677     <thead>
4678      <row>
4679       <entry>Name</entry>
4680       <entry>Type</entry>
4681       <entry>References</entry>
4682       <entry>Description</entry>
4683      </row>
4684     </thead>
4685
4686     <tbody>
4687      <row>
4688       <entry><structfield>dictname</structfield></entry>
4689       <entry><type>name</type></entry>
4690       <entry></entry>
4691       <entry>Text search dictionary name</entry>
4692      </row>
4693
4694      <row>
4695       <entry><structfield>dictnamespace</structfield></entry>
4696       <entry><type>oid</type></entry>
4697       <entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.oid</literal></entry>
4698       <entry>
4699        The OID of the namespace that contains this dictionary
4700       </entry>
4701      </row>
4702
4703      <row>
4704       <entry><structfield>dictowner</structfield></entry>
4705       <entry><type>oid</type></entry>
4706       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
4707       <entry>Owner of the dictionary</entry>
4708      </row>
4709
4710      <row>
4711       <entry><structfield>dicttemplate</structfield></entry>
4712       <entry><type>oid</type></entry>
4713       <entry><literal><link linkend="catalog-pg-ts-template"><structname>pg_ts_template</structname></link>.oid</literal></entry>
4714       <entry>The OID of the text search template for this dictionary</entry>
4715      </row>
4716
4717      <row>
4718       <entry><structfield>dictinitoption</structfield></entry>
4719       <entry><type>text</type></entry>
4720       <entry></entry>
4721       <entry>Initialization option string for the template</entry>
4722      </row>
4723     </tbody>
4724    </tgroup>
4725   </table>
4726  </sect1>
4727
4728
4729  <sect1 id="catalog-pg-ts-parser">
4730   <title><structname>pg_ts_parser</structname></title>
4731
4732   <indexterm zone="catalog-pg-ts-parser">
4733    <primary>pg_ts_parser</primary>
4734   </indexterm>
4735
4736   <para>
4737    The <structname>pg_ts_parser</structname> catalog contains entries
4738    defining text search parsers.  A parser is responsible for splitting
4739    input text into lexemes and assigning a token type to each lexeme.
4740    Since a parser must be implemented by C-language-level functions,
4741    creation of new parsers is restricted to database superusers.
4742   </para>
4743
4744   <para>
4745    <productname>PostgreSQL</productname>'s text search features are
4746    described at length in <xref linkend="textsearch">.
4747   </para>
4748
4749   <table>
4750    <title><structname>pg_ts_parser</> Columns</title>
4751
4752    <tgroup cols=4>
4753     <thead>
4754      <row>
4755       <entry>Name</entry>
4756       <entry>Type</entry>
4757       <entry>References</entry>
4758       <entry>Description</entry>
4759      </row>
4760     </thead>
4761
4762     <tbody>
4763      <row>
4764       <entry><structfield>prsname</structfield></entry>
4765       <entry><type>name</type></entry>
4766       <entry></entry>
4767       <entry>Text search parser name</entry>
4768      </row>
4769
4770      <row>
4771       <entry><structfield>prsnamespace</structfield></entry>
4772       <entry><type>oid</type></entry>
4773       <entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.oid</literal></entry>
4774       <entry>
4775        The OID of the namespace that contains this parser
4776       </entry>
4777      </row>
4778
4779      <row>
4780       <entry><structfield>prsstart</structfield></entry>
4781       <entry><type>regproc</type></entry>
4782       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
4783       <entry>OID of the parser's startup function</entry>
4784      </row>
4785
4786      <row>
4787       <entry><structfield>prstoken</structfield></entry>
4788       <entry><type>regproc</type></entry>
4789       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
4790       <entry>OID of the parser's next-token function</entry>
4791      </row>
4792
4793      <row>
4794       <entry><structfield>prsend</structfield></entry>
4795       <entry><type>regproc</type></entry>
4796       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
4797       <entry>OID of the parser's shutdown function</entry>
4798      </row>
4799
4800      <row>
4801       <entry><structfield>prsheadline</structfield></entry>
4802       <entry><type>regproc</type></entry>
4803       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
4804       <entry>OID of the parser's headline function</entry>
4805      </row>
4806
4807      <row>
4808       <entry><structfield>prslextype</structfield></entry>
4809       <entry><type>regproc</type></entry>
4810       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
4811       <entry>OID of the parser's lextype function</entry>
4812      </row>
4813     </tbody>
4814    </tgroup>
4815   </table>
4816  </sect1>
4817
4818
4819  <sect1 id="catalog-pg-ts-template">
4820   <title><structname>pg_ts_template</structname></title>
4821
4822   <indexterm zone="catalog-pg-ts-template">
4823    <primary>pg_ts_template</primary>
4824   </indexterm>
4825
4826   <para>
4827    The <structname>pg_ts_template</structname> catalog contains entries
4828    defining text search templates.  A template is the implementation
4829    skeleton for a class of text search dictionaries.
4830    Since a template must be implemented by C-language-level functions,
4831    creation of new templates is restricted to database superusers.
4832   </para>
4833
4834   <para>
4835    <productname>PostgreSQL</productname>'s text search features are
4836    described at length in <xref linkend="textsearch">.
4837   </para>
4838
4839   <table>
4840    <title><structname>pg_ts_template</> Columns</title>
4841
4842    <tgroup cols=4>
4843     <thead>
4844      <row>
4845       <entry>Name</entry>
4846       <entry>Type</entry>
4847       <entry>References</entry>
4848       <entry>Description</entry>
4849      </row>
4850     </thead>
4851
4852     <tbody>
4853      <row>
4854       <entry><structfield>tmplname</structfield></entry>
4855       <entry><type>name</type></entry>
4856       <entry></entry>
4857       <entry>Text search template name</entry>
4858      </row>
4859
4860      <row>
4861       <entry><structfield>tmplnamespace</structfield></entry>
4862       <entry><type>oid</type></entry>
4863       <entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.oid</literal></entry>
4864       <entry>
4865        The OID of the namespace that contains this template
4866       </entry>
4867      </row>
4868
4869      <row>
4870       <entry><structfield>tmplinit</structfield></entry>
4871       <entry><type>regproc</type></entry>
4872       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
4873       <entry>OID of the template's initialization function</entry>
4874      </row>
4875
4876      <row>
4877       <entry><structfield>tmpllexize</structfield></entry>
4878       <entry><type>regproc</type></entry>
4879       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
4880       <entry>OID of the template's lexize function</entry>
4881      </row>
4882     </tbody>
4883    </tgroup>
4884   </table>
4885  </sect1>
4886
4887
4888  <sect1 id="catalog-pg-type">
4889   <title><structname>pg_type</structname></title>
4890
4891   <indexterm zone="catalog-pg-type">
4892    <primary>pg_type</primary>
4893   </indexterm>
4894
4895   <para>
4896    The catalog <structname>pg_type</structname> stores information about data
4897    types.  Base types and enum types (scalar types) are created with
4898    <xref linkend="sql-createtype" endterm="sql-createtype-title">, and
4899    domains with
4900    <xref linkend="sql-createdomain" endterm="sql-createdomain-title">.
4901    A composite type is automatically created for each table in the database, to
4902    represent the row structure of the table.  It is also possible to create
4903    composite types with <command>CREATE TYPE AS</command>.
4904   </para>
4905
4906   <table>
4907    <title><structname>pg_type</> Columns</title>
4908
4909    <tgroup cols=4>
4910     <thead>
4911      <row>
4912       <entry>Name</entry>
4913       <entry>Type</entry>
4914       <entry>References</entry>
4915       <entry>Description</entry>
4916      </row>
4917     </thead>
4918
4919     <tbody>
4920      <row>
4921       <entry><structfield>typname</structfield></entry>
4922       <entry><type>name</type></entry>
4923       <entry></entry>
4924       <entry>Data type name</entry>
4925      </row>
4926
4927      <row>
4928       <entry><structfield>typnamespace</structfield></entry>
4929       <entry><type>oid</type></entry>
4930       <entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.oid</literal></entry>
4931       <entry>
4932        The OID of the namespace that contains this type
4933       </entry>
4934      </row>
4935
4936      <row>
4937       <entry><structfield>typowner</structfield></entry>
4938       <entry><type>oid</type></entry>
4939       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
4940       <entry>Owner of the type</entry>
4941      </row>
4942
4943      <row>
4944       <entry><structfield>typlen</structfield></entry>
4945       <entry><type>int2</type></entry>
4946       <entry></entry>
4947       <entry>
4948        For a fixed-size type, <structfield>typlen</structfield> is the number
4949        of bytes in the internal representation of the type.  But for a
4950        variable-length type, <structfield>typlen</structfield> is negative.
4951        -1 indicates a <quote>varlena</> type (one that has a length word),
4952        -2 indicates a null-terminated C string.
4953       </entry>
4954      </row>
4955
4956      <row>
4957       <entry><structfield>typbyval</structfield></entry>
4958       <entry><type>bool</type></entry>
4959       <entry></entry>
4960       <entry>
4961        <structfield>typbyval</structfield> determines whether internal
4962        routines pass a value of this type by value or by reference.
4963        <structfield>typbyval</structfield> had better be false if
4964        <structfield>typlen</structfield> is not 1, 2, or 4 (or 8 on machines
4965        where Datum is 8 bytes).
4966        Variable-length types are always passed by reference. Note that
4967        <structfield>typbyval</structfield> can be false even if the
4968        length would allow pass-by-value
4969       </entry>
4970      </row>
4971
4972      <row>
4973       <entry><structfield>typtype</structfield></entry>
4974       <entry><type>char</type></entry>
4975       <entry></entry>
4976       <entry>
4977        <structfield>typtype</structfield> is
4978        <literal>b</literal> for a base type,
4979        <literal>c</literal> for a composite type (e.g., a table's row type),
4980        <literal>d</literal> for a domain,
4981        <literal>e</literal> for an enum type,
4982        or <literal>p</literal> for a pseudo-type.
4983        See also <structfield>typrelid</structfield> and
4984        <structfield>typbasetype</structfield>
4985       </entry>
4986      </row>
4987
4988      <row>
4989       <entry><structfield>typcategory</structfield></entry>
4990       <entry><type>char</type></entry>
4991       <entry></entry>
4992       <entry>
4993        <structfield>typcategory</structfield> is an arbitrary classification
4994        of data types that is used by the parser to determine which implicit
4995        casts should be <quote>preferred</>.
4996        See <xref linkend="catalog-typcategory-table">
4997       </entry>
4998      </row>
4999
5000      <row>
5001       <entry><structfield>typispreferred</structfield></entry>
5002       <entry><type>bool</type></entry>
5003       <entry></entry>
5004       <entry>
5005        True if the type is a preferred cast target within its
5006        <structfield>typcategory</structfield>
5007       </entry>
5008      </row>
5009
5010      <row>
5011       <entry><structfield>typisdefined</structfield></entry>
5012       <entry><type>bool</type></entry>
5013       <entry></entry>
5014       <entry>
5015        True if the type is defined, false if this is a placeholder
5016        entry for a not-yet-defined type.  When
5017        <structfield>typisdefined</structfield> is false, nothing
5018        except the type name, namespace, and OID can be relied on
5019       </entry>
5020      </row>
5021
5022      <row>
5023       <entry><structfield>typdelim</structfield></entry>
5024       <entry><type>char</type></entry>
5025       <entry></entry>
5026       <entry>
5027        Character that separates two values of this type when parsing
5028        array input.  Note that the delimiter is associated with the array
5029        element data type, not the array data type
5030       </entry>
5031      </row>
5032
5033      <row>
5034       <entry><structfield>typrelid</structfield></entry>
5035       <entry><type>oid</type></entry>
5036       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
5037       <entry>
5038        If this is a composite type (see
5039        <structfield>typtype</structfield>), then this column points to
5040        the <structname>pg_class</structname> entry that defines the
5041        corresponding table.  (For a free-standing composite type, the
5042        <structname>pg_class</structname> entry doesn't really represent
5043        a table, but it is needed anyway for the type's
5044        <structname>pg_attribute</structname> entries to link to.)
5045        Zero for non-composite types
5046       </entry>
5047      </row>
5048
5049      <row>
5050       <entry><structfield>typelem</structfield></entry>
5051       <entry><type>oid</type></entry>
5052       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
5053       <entry>
5054        If <structfield>typelem</structfield> is not 0 then it
5055        identifies another row in <structname>pg_type</structname>.
5056        The current type can then be subscripted like an array yielding
5057        values of type <structfield>typelem</structfield>.  A
5058        <quote>true</quote> array type is variable length
5059        (<structfield>typlen</structfield> = -1),
5060        but some fixed-length (<structfield>typlen</structfield> &gt; 0) types
5061        also have nonzero <structfield>typelem</structfield>, for example
5062        <type>name</type> and <type>point</type>.
5063        If a fixed-length type has a <structfield>typelem</structfield> then
5064        its internal representation must be some number of values of the
5065        <structfield>typelem</structfield> data type with no other data.
5066        Variable-length array types have a header defined by the array
5067        subroutines
5068       </entry>
5069      </row>
5070
5071      <row>
5072       <entry><structfield>typarray</structfield></entry>
5073       <entry><type>oid</type></entry>
5074       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
5075       <entry>
5076        If <structfield>typarray</structfield> is not 0 then it
5077        identifies another row in <structname>pg_type</structname>, which
5078        is the <quote>true</quote> array type having this type as element
5079       </entry>
5080      </row>
5081
5082      <row>
5083       <entry><structfield>typinput</structfield></entry>
5084       <entry><type>regproc</type></entry>
5085       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
5086       <entry>Input conversion function (text format)</entry>
5087      </row>
5088
5089      <row>
5090       <entry><structfield>typoutput</structfield></entry>
5091       <entry><type>regproc</type></entry>
5092       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
5093       <entry>Output conversion function (text format)</entry>
5094      </row>
5095
5096      <row>
5097       <entry><structfield>typreceive</structfield></entry>
5098       <entry><type>regproc</type></entry>
5099       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
5100       <entry>Input conversion function (binary format), or 0 if none</entry>
5101      </row>
5102
5103      <row>
5104       <entry><structfield>typsend</structfield></entry>
5105       <entry><type>regproc</type></entry>
5106       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
5107       <entry>Output conversion function (binary format), or 0 if none</entry>
5108      </row>
5109
5110      <row>
5111       <entry><structfield>typmodin</structfield></entry>
5112       <entry><type>regproc</type></entry>
5113       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
5114       <entry>Type modifier input function, or 0 if type does not support modifiers</entry>
5115      </row>
5116
5117      <row>
5118       <entry><structfield>typmodout</structfield></entry>
5119       <entry><type>regproc</type></entry>
5120       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
5121       <entry>Type modifier output function, or 0 to use the standard format</entry>
5122      </row>
5123
5124      <row>
5125       <entry><structfield>typanalyze</structfield></entry>
5126       <entry><type>regproc</type></entry>
5127       <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
5128       <entry>Custom ANALYZE function, or 0 to use the standard function</entry>
5129      </row>
5130
5131      <row>
5132       <entry><structfield>typalign</structfield></entry>
5133       <entry><type>char</type></entry>
5134       <entry></entry>
5135       <entry><para>
5136
5137        <structfield>typalign</structfield> is the alignment required
5138        when storing a value of this type.  It applies to storage on
5139        disk as well as most representations of the value inside
5140        <productname>PostgreSQL</>.
5141        When multiple values are stored consecutively, such
5142        as in the representation of a complete row on disk, padding is
5143        inserted before a datum of this type so that it begins on the
5144        specified boundary.  The alignment reference is the beginning
5145        of the first datum in the sequence.
5146       </para><para>
5147        Possible values are:
5148        <itemizedlist>
5149         <listitem>
5150          <para><literal>c</> = <type>char</type> alignment, i.e., no alignment needed.</para>
5151         </listitem>
5152         <listitem>
5153          <para><literal>s</> = <type>short</type> alignment (2 bytes on most machines).</para>
5154         </listitem>
5155         <listitem>
5156          <para><literal>i</> = <type>int</type> alignment (4 bytes on most machines).</para>
5157         </listitem>
5158         <listitem>
5159          <para><literal>d</> = <type>double</type> alignment (8 bytes on many machines, but by no means all).</para>
5160         </listitem>
5161        </itemizedlist>
5162       </para><note>
5163        <para>
5164         For types used in system tables, it is critical that the size
5165         and alignment defined in <structname>pg_type</structname>
5166         agree with the way that the compiler will lay out the column in
5167         a structure representing a table row.
5168        </para>
5169       </note></entry>
5170      </row>
5171
5172      <row>
5173       <entry><structfield>typstorage</structfield></entry>
5174       <entry><type>char</type></entry>
5175       <entry></entry>
5176       <entry><para>
5177        <structfield>typstorage</structfield> tells for varlena
5178        types (those with <structfield>typlen</structfield> = -1) if
5179        the type is prepared for toasting and what the default strategy
5180        for attributes of this type should be.
5181        Possible values are
5182        <itemizedlist>
5183         <listitem>
5184          <para><literal>p</>: Value must always be stored plain.</para>
5185         </listitem>
5186         <listitem>
5187          <para>
5188           <literal>e</>: Value can be stored in a <quote>secondary</quote>
5189           relation (if relation has one, see
5190           <literal>pg_class.reltoastrelid</literal>).
5191          </para>
5192         </listitem>
5193         <listitem>
5194          <para><literal>m</>: Value can be stored compressed inline.</para>
5195         </listitem>
5196         <listitem>
5197          <para><literal>x</>: Value can be stored compressed inline or stored in <quote>secondary</quote> storage.</para>
5198         </listitem>
5199        </itemizedlist>
5200        Note that <literal>m</> columns can also be moved out to secondary
5201        storage, but only as a last resort (<literal>e</> and <literal>x</> columns are
5202        moved first).
5203       </para></entry>
5204      </row>
5205
5206      <row>
5207       <entry><structfield>typnotnull</structfield></entry>
5208       <entry><type>bool</type></entry>
5209       <entry></entry>
5210       <entry><para>
5211        <structfield>typnotnull</structfield> represents a not-null
5212        constraint on a type.  Used for domains only
5213       </para></entry>
5214      </row>
5215
5216      <row>
5217       <entry><structfield>typbasetype</structfield></entry>
5218       <entry><type>oid</type></entry>
5219       <entry><literal><link linkend="catalog-pg-type"><structname>pg_type</structname></link>.oid</literal></entry>
5220       <entry><para>
5221        If this is a domain (see <structfield>typtype</structfield>), then
5222        <structfield>typbasetype</structfield> identifies the type that this
5223        one is based on.  Zero if this type is not a domain
5224       </para></entry>
5225      </row>
5226
5227      <row>
5228       <entry><structfield>typtypmod</structfield></entry>
5229       <entry><type>int4</type></entry>
5230       <entry></entry>
5231       <entry><para>
5232        Domains use <structfield>typtypmod</structfield> to record the <literal>typmod</>
5233        to be applied to their base type (-1 if base type does not use a
5234        <literal>typmod</>).  -1 if this type is not a domain
5235       </para></entry>
5236      </row>
5237
5238      <row>
5239       <entry><structfield>typndims</structfield></entry>
5240       <entry><type>int4</type></entry>
5241       <entry></entry>
5242       <entry><para>
5243        <structfield>typndims</structfield> is the number of array dimensions
5244        for a domain that is an array (that is, <structfield>typbasetype</> is
5245        an array type; the domain's <structfield>typelem</> will match the base
5246        type's <structfield>typelem</structfield>).
5247        Zero for types other than domains over array types
5248        </para></entry>
5249      </row>
5250
5251      <row>
5252       <entry><structfield>typdefaultbin</structfield></entry>
5253       <entry><type>text</type></entry>
5254       <entry></entry>
5255       <entry><para>
5256        If <structfield>typdefaultbin</> is not null, it is the <function>nodeToString()</function>
5257        representation of a default expression for the type.  This is
5258        only used for domains
5259       </para></entry>
5260      </row>
5261
5262      <row>
5263       <entry><structfield>typdefault</structfield></entry>
5264       <entry><type>text</type></entry>
5265       <entry></entry>
5266       <entry><para>
5267        <structfield>typdefault</> is null if the type has no associated
5268        default value. If <structfield>typdefaultbin</> is not null,
5269        <structfield>typdefault</> must contain a human-readable version of the
5270        default expression represented by <structfield>typdefaultbin</>.  If
5271        <structfield>typdefaultbin</> is null and <structfield>typdefault</> is
5272        not, then <structfield>typdefault</> is the external representation of
5273        the type's default value, which might be fed to the type's input
5274        converter to produce a constant
5275       </para></entry>
5276      </row>
5277     </tbody>
5278    </tgroup>
5279   </table>
5280
5281   <para>
5282    <xref linkend="catalog-typcategory-table"> lists the system-defined values
5283    of <structfield>typcategory</>.  Any future additions to this list will
5284    also be upper-case ASCII letters.  All other ASCII characters are reserved
5285    for user-defined categories.
5286   </para>
5287
5288   <table id="catalog-typcategory-table">
5289    <title><structfield>typcategory</> Codes</title>
5290
5291    <tgroup cols=2>
5292     <thead>
5293      <row>
5294       <entry>Code</entry>
5295       <entry>Category</entry>
5296      </row>
5297     </thead>
5298
5299     <tbody>
5300      <row>
5301       <entry><literal>A</literal></entry>
5302       <entry>Array types</entry>
5303      </row>
5304      <row>
5305       <entry><literal>B</literal></entry>
5306       <entry>Boolean types</entry>
5307      </row>
5308      <row>
5309       <entry><literal>C</literal></entry>
5310       <entry>Composite types</entry>
5311      </row>
5312      <row>
5313       <entry><literal>D</literal></entry>
5314       <entry>Date/time types</entry>
5315      </row>
5316      <row>
5317       <entry><literal>E</literal></entry>
5318       <entry>Enum types</entry>
5319      </row>
5320      <row>
5321       <entry><literal>G</literal></entry>
5322       <entry>Geometric types</entry>
5323      </row>
5324      <row>
5325       <entry><literal>I</literal></entry>
5326       <entry>Network address types</entry>
5327      </row>
5328      <row>
5329       <entry><literal>N</literal></entry>
5330       <entry>Numeric types</entry>
5331      </row>
5332      <row>
5333       <entry><literal>P</literal></entry>
5334       <entry>Pseudo-types</entry>
5335      </row>
5336      <row>
5337       <entry><literal>S</literal></entry>
5338       <entry>String types</entry>
5339      </row>
5340      <row>
5341       <entry><literal>T</literal></entry>
5342       <entry>Timespan types</entry>
5343      </row>
5344      <row>
5345       <entry><literal>U</literal></entry>
5346       <entry>User-defined types</entry>
5347      </row>
5348      <row>
5349       <entry><literal>V</literal></entry>
5350       <entry>Bit-string types</entry>
5351      </row>
5352      <row>
5353       <entry><literal>X</literal></entry>
5354       <entry><type>unknown</> type</entry>
5355      </row>
5356     </tbody>
5357    </tgroup>
5358   </table>
5359
5360  </sect1>
5361
5362  <sect1 id="views-overview">
5363   <title>System Views</title>
5364
5365   <para>
5366    In addition to the system catalogs, <productname>PostgreSQL</productname>
5367    provides a number of built-in views.  Some system views provide convenient
5368    access to some commonly used queries on the system catalogs.  Other views
5369    provide access to internal server state.
5370   </para>
5371
5372   <para>
5373    The information schema (<xref linkend="information-schema">) provides
5374    an alternative set of views which overlap the functionality of the system
5375    views.  Since the information schema is SQL-standard whereas the views
5376    described here are <productname>PostgreSQL</productname>-specific,
5377    it's usually better to use the information schema if it provides all
5378    the information you need.
5379   </para>
5380
5381   <para>
5382    <xref linkend="view-table"> lists the system views described here.
5383    More detailed documentation of each view follows below.
5384    There are some additional views that provide access to the results of
5385    the statistics collector; they are described in <xref
5386    linkend="monitoring-stats-views-table">.
5387   </para>
5388
5389   <para>
5390    Except where noted, all the views described here are read-only.
5391   </para>
5392
5393   <table id="view-table">
5394    <title>System Views</title>
5395
5396    <tgroup cols="2">
5397     <thead>
5398      <row>
5399       <entry>View Name</entry>
5400       <entry>Purpose</entry>
5401      </row>
5402     </thead>
5403
5404     <tbody>
5405      <row>
5406       <entry><link linkend="view-pg-cursors"><structname>pg_cursors</structname></link></entry>
5407       <entry>open cursors</entry>
5408      </row>
5409
5410      <row>
5411       <entry><link linkend="view-pg-group"><structname>pg_group</structname></link></entry>
5412       <entry>groups of database users</entry>
5413      </row>
5414
5415      <row>
5416       <entry><link linkend="view-pg-indexes"><structname>pg_indexes</structname></link></entry>
5417       <entry>indexes</entry>
5418      </row>
5419
5420      <row>
5421       <entry><link linkend="view-pg-locks"><structname>pg_locks</structname></link></entry>
5422       <entry>currently held locks</entry>
5423      </row>
5424
5425      <row>
5426       <entry><link linkend="view-pg-prepared-statements"><structname>pg_prepared_statements</structname></link></entry>
5427       <entry>prepared statements</entry>
5428      </row>
5429
5430      <row>
5431       <entry><link linkend="view-pg-prepared-xacts"><structname>pg_prepared_xacts</structname></link></entry>
5432       <entry>prepared transactions</entry>
5433      </row>
5434
5435      <row>
5436       <entry><link linkend="view-pg-roles"><structname>pg_roles</structname></link></entry>
5437       <entry>database roles</entry>
5438      </row>
5439
5440      <row>
5441       <entry><link linkend="view-pg-rules"><structname>pg_rules</structname></link></entry>
5442       <entry>rules</entry>
5443      </row>
5444
5445      <row>
5446       <entry><link linkend="view-pg-settings"><structname>pg_settings</structname></link></entry>
5447       <entry>parameter settings</entry>
5448      </row>
5449
5450      <row>
5451       <entry><link linkend="view-pg-shadow"><structname>pg_shadow</structname></link></entry>
5452       <entry>database users</entry>
5453      </row>
5454
5455      <row>
5456       <entry><link linkend="view-pg-stats"><structname>pg_stats</structname></link></entry>
5457       <entry>planner statistics</entry>
5458      </row>
5459
5460      <row>
5461       <entry><link linkend="view-pg-tables"><structname>pg_tables</structname></link></entry>
5462       <entry>tables</entry>
5463      </row>
5464
5465      <row>
5466       <entry><link linkend="view-pg-timezone-abbrevs"><structname>pg_timezone_abbrevs</structname></link></entry>
5467       <entry>time zone abbreviations</entry>
5468      </row>
5469
5470      <row>
5471       <entry><link linkend="view-pg-timezone-names"><structname>pg_timezone_names</structname></link></entry>
5472       <entry>time zone names</entry>
5473      </row>
5474
5475      <row>
5476       <entry><link linkend="view-pg-user"><structname>pg_user</structname></link></entry>
5477       <entry>database users</entry>
5478      </row>
5479
5480      <row>
5481       <entry><link linkend="view-pg-views"><structname>pg_views</structname></link></entry>
5482       <entry>views</entry>
5483      </row>
5484
5485     </tbody>
5486    </tgroup>
5487   </table>
5488  </sect1>
5489
5490  <sect1 id="view-pg-cursors">
5491   <title><structname>pg_cursors</structname></title>
5492
5493   <indexterm zone="view-pg-cursors">
5494    <primary>pg_cursors</primary>
5495   </indexterm>
5496
5497   <para>
5498    The <structname>pg_cursors</structname> view lists the cursors that
5499    are currently available. Cursors can be defined in several ways:
5500    <itemizedlist>
5501     <listitem>
5502      <para>
5503       via the <xref linkend="sql-declare" endterm="sql-declare-title">
5504       statement in SQL
5505      </para>
5506     </listitem>
5507
5508     <listitem>
5509      <para>
5510       via the Bind message in the frontend/backend protocol, as
5511       described in <xref linkend="protocol-flow-ext-query">
5512      </para>
5513     </listitem>
5514
5515     <listitem>
5516      <para>
5517       via the Server Programming Interface (SPI), as described in
5518       <xref linkend="spi-interface">
5519      </para>
5520     </listitem>
5521    </itemizedlist>
5522
5523    The <structname>pg_cursors</structname> view displays cursors
5524    created by any of these means. Cursors only exist for the duration
5525    of the transaction that defines them, unless they have been
5526    declared <literal>WITH HOLD</literal>. Therefore non-holdable
5527    cursors are only present in the view until the end of their
5528    creating transaction.
5529
5530    <note>
5531     <para>
5532      Cursors are used internally to implement some of the components
5533      of <productname>PostgreSQL</>, such as procedural languages.
5534      Therefore, the <structname>pg_cursors</> view might include cursors
5535      that have not been explicitly created by the user.
5536     </para>
5537    </note>
5538   </para>
5539
5540   <table>
5541    <title><structname>pg_cursors</> Columns</title>
5542
5543    <tgroup cols=3>
5544     <thead>
5545      <row>
5546       <entry>Name</entry>
5547       <entry>Type</entry>
5548       <entry>Description</entry>
5549      </row>
5550     </thead>
5551
5552     <tbody>
5553      <row>
5554       <entry><structfield>name</structfield></entry>
5555       <entry><type>text</type></entry>
5556       <entry>The name of the cursor</entry>
5557      </row>
5558
5559      <row>
5560       <entry><structfield>statement</structfield></entry>
5561       <entry><type>text</type></entry>
5562       <entry>The verbatim query string submitted to declare this cursor</entry>
5563      </row>
5564
5565      <row>
5566       <entry><structfield>is_holdable</structfield></entry>
5567       <entry><type>boolean</type></entry>
5568       <entry>
5569        <literal>true</literal> if the cursor is holdable (that is, it
5570        can be accessed after the transaction that declared the cursor
5571        has committed); <literal>false</literal> otherwise
5572        </entry>
5573      </row>
5574
5575      <row>
5576       <entry><structfield>is_binary</structfield></entry>
5577       <entry><type>boolean</type></entry>
5578       <entry>
5579        <literal>true</literal> if the cursor was declared
5580        <literal>BINARY</literal>; <literal>false</literal>
5581        otherwise
5582        </entry>
5583      </row>
5584
5585      <row>
5586       <entry><structfield>is_scrollable</structfield></entry>
5587       <entry><type>boolean</type></entry>
5588       <entry>
5589        <literal>true</> if the cursor is scrollable (that is, it
5590        allows rows to be retrieved in a nonsequential manner);
5591        <literal>false</literal> otherwise
5592        </entry>
5593      </row>
5594
5595      <row>
5596       <entry><structfield>creation_time</structfield></entry>
5597       <entry><type>timestamptz</type></entry>
5598       <entry>The time at which the cursor was declared</entry>
5599      </row>
5600     </tbody>
5601    </tgroup>
5602   </table>
5603
5604   <para>
5605    The <structname>pg_cursors</structname> view is read only.
5606   </para>
5607
5608  </sect1>
5609
5610  <sect1 id="view-pg-group">
5611   <title><structname>pg_group</structname></title>
5612
5613   <indexterm zone="view-pg-group">
5614    <primary>pg_group</primary>
5615   </indexterm>
5616
5617   <para>
5618    The view <structname>pg_group</structname> exists for backwards
5619    compatibility: it emulates a catalog that existed in
5620    <productname>PostgreSQL</productname> before version 8.1.
5621    It shows the names and members of all roles that are marked as not
5622    <structfield>rolcanlogin</>, which is an approximation to the set
5623    of roles that are being used as groups.
5624   </para>
5625
5626   <table>
5627    <title><structname>pg_group</> Columns</title>
5628
5629    <tgroup cols=4>
5630     <thead>
5631      <row>
5632       <entry>Name</entry>
5633       <entry>Type</entry>
5634       <entry>References</entry>
5635       <entry>Description</entry>
5636      </row>
5637     </thead>
5638
5639     <tbody>
5640      <row>
5641       <entry><structfield>groname</structfield></entry>
5642       <entry><type>name</type></entry>
5643       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.rolname</literal></entry>
5644       <entry>Name of the group</entry>
5645      </row>
5646
5647      <row>
5648       <entry><structfield>grosysid</structfield></entry>
5649       <entry><type>oid</type></entry>
5650       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
5651       <entry>ID of this group</entry>
5652      </row>
5653
5654      <row>
5655       <entry><structfield>grolist</structfield></entry>
5656       <entry><type>oid[]</type></entry>
5657       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
5658       <entry>An array containing the IDs of the roles in this group</entry>
5659      </row>
5660     </tbody>
5661    </tgroup>
5662   </table>
5663
5664  </sect1>
5665
5666  <sect1 id="view-pg-indexes">
5667   <title><structname>pg_indexes</structname></title>
5668
5669   <indexterm zone="view-pg-indexes">
5670    <primary>pg_indexes</primary>
5671   </indexterm>
5672
5673   <para>
5674    The view <structname>pg_indexes</structname> provides access to
5675    useful information about each index in the database.
5676   </para>
5677
5678   <table>
5679    <title><structname>pg_indexes</> Columns</title>
5680
5681    <tgroup cols=4>
5682     <thead>
5683      <row>
5684       <entry>Name</entry>
5685       <entry>Type</entry>
5686       <entry>References</entry>
5687       <entry>Description</entry>
5688      </row>
5689     </thead>
5690     <tbody>
5691      <row>
5692       <entry><structfield>schemaname</structfield></entry>
5693       <entry><type>name</type></entry>
5694       <entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.nspname</literal></entry>
5695       <entry>Name of schema containing table and index</entry>
5696      </row>
5697      <row>
5698       <entry><structfield>tablename</structfield></entry>
5699       <entry><type>name</type></entry>
5700       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.relname</literal></entry>
5701       <entry>Name of table the index is for</entry>
5702      </row>
5703      <row>
5704       <entry><structfield>indexname</structfield></entry>
5705       <entry><type>name</type></entry>
5706       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.relname</literal></entry>
5707       <entry>Name of index</entry>
5708      </row>
5709      <row>
5710       <entry><structfield>tablespace</structfield></entry>
5711       <entry><type>name</type></entry>
5712       <entry><literal><link linkend="catalog-pg-tablespace"><structname>pg_tablespace</structname></link>.spcname</literal></entry>
5713       <entry>Name of tablespace containing index (NULL if default for database)</entry>
5714      </row>
5715      <row>
5716       <entry><structfield>indexdef</structfield></entry>
5717       <entry><type>text</type></entry>
5718       <entry></entry>
5719       <entry>Index definition (a reconstructed <command>CREATE INDEX</command>
5720       command)</entry>
5721      </row>
5722     </tbody>
5723    </tgroup>
5724   </table>
5725
5726  </sect1>
5727
5728  <sect1 id="view-pg-locks">
5729   <title><structname>pg_locks</structname></title>
5730
5731   <indexterm zone="view-pg-locks">
5732    <primary>pg_locks</primary>
5733   </indexterm>
5734
5735   <para>
5736    The view <structname>pg_locks</structname> provides access to
5737    information about the locks held by open transactions within the
5738    database server.  See <xref linkend="mvcc"> for more discussion
5739    of locking.
5740   </para>
5741
5742   <para>
5743    <structname>pg_locks</structname> contains one row per active lockable
5744    object, requested lock mode, and relevant transaction.  Thus, the same
5745    lockable object might
5746    appear many times, if multiple transactions are holding or waiting
5747    for locks on it.  However, an object that currently has no locks on it
5748    will not appear at all.
5749   </para>
5750
5751   <para>
5752    There are several distinct types of lockable objects:
5753    whole relations (e.g., tables), individual pages of relations,
5754    individual tuples of relations,
5755    transaction IDs (both virtual and permanent IDs),
5756    and general database objects (identified by class OID and object OID,
5757    in the same way as in <structname>pg_description</structname> or
5758    <structname>pg_depend</structname>).  Also, the right to extend a
5759    relation is represented as a separate lockable object.
5760   </para>
5761
5762   <table>
5763    <title><structname>pg_locks</> Columns</title>
5764
5765    <tgroup cols=4>
5766     <thead>
5767      <row>
5768       <entry>Name</entry>
5769       <entry>Type</entry>
5770       <entry>References</entry>
5771       <entry>Description</entry>
5772      </row>
5773     </thead>
5774     <tbody>
5775      <row>
5776       <entry><structfield>locktype</structfield></entry>
5777       <entry><type>text</type></entry>
5778       <entry></entry>
5779       <entry>
5780        type of the lockable object:
5781        <literal>relation</>,
5782        <literal>extend</>,
5783        <literal>page</>,
5784        <literal>tuple</>,
5785        <literal>transactionid</>,
5786        <literal>virtualxid</>,
5787        <literal>object</>,
5788        <literal>userlock</>, or
5789        <literal>advisory</>
5790       </entry>
5791      </row>
5792      <row>
5793       <entry><structfield>database</structfield></entry>
5794       <entry><type>oid</type></entry>
5795       <entry><literal><link linkend="catalog-pg-database"><structname>pg_database</structname></link>.oid</literal></entry>
5796       <entry>
5797        OID of the database in which the object exists, or
5798        zero if the object is a shared object, or
5799        NULL if the object is a transaction ID
5800       </entry>
5801      </row>
5802      <row>
5803       <entry><structfield>relation</structfield></entry>
5804       <entry><type>oid</type></entry>
5805       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
5806       <entry>
5807        OID of the relation, or NULL if the object is not
5808        a relation or part of a relation
5809       </entry>
5810      </row>
5811      <row>
5812       <entry><structfield>page</structfield></entry>
5813       <entry><type>integer</type></entry>
5814       <entry></entry>
5815       <entry>
5816        Page number within the relation, or NULL if the object
5817        is not a tuple or relation page
5818       </entry>
5819      </row>
5820      <row>
5821       <entry><structfield>tuple</structfield></entry>
5822       <entry><type>smallint</type></entry>
5823       <entry></entry>
5824       <entry>
5825        Tuple number within the page, or NULL if the object is not a tuple
5826       </entry>
5827      </row>
5828      <row>
5829       <entry><structfield>virtualxid</structfield></entry>
5830       <entry><type>text</type></entry>
5831       <entry></entry>
5832       <entry>
5833        Virtual ID of a transaction, or NULL if the object is not a
5834        virtual transaction ID
5835       </entry>
5836      </row>
5837      <row>
5838       <entry><structfield>transactionid</structfield></entry>
5839       <entry><type>xid</type></entry>
5840       <entry></entry>
5841       <entry>
5842        ID of a transaction, or NULL if the object is not a transaction ID
5843       </entry>
5844      </row>
5845      <row>
5846       <entry><structfield>classid</structfield></entry>
5847       <entry><type>oid</type></entry>
5848       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
5849       <entry>
5850        OID of the system catalog containing the object, or NULL if the
5851        object is not a general database object
5852       </entry>
5853      </row>
5854      <row>
5855       <entry><structfield>objid</structfield></entry>
5856       <entry><type>oid</type></entry>
5857       <entry>any OID column</entry>
5858       <entry>
5859        OID of the object within its system catalog, or NULL if the
5860        object is not a general database object.
5861        For advisory locks it is used to distinguish the two key
5862        spaces (<literal>1</> for an int8 key, <literal>2</> for two
5863        int4 keys).
5864       </entry>
5865      </row>
5866      <row>
5867       <entry><structfield>objsubid</structfield></entry>
5868       <entry><type>smallint</type></entry>
5869       <entry></entry>
5870       <entry>
5871        For a table column, this is the column number (the
5872        <structfield>classid</> and <structfield>objid</> refer to the
5873        table itself).  For all other object types, this column is
5874        zero.  NULL if the object is not a general database object
5875       </entry>
5876      </row>
5877      <row>
5878       <entry><structfield>virtualtransaction</structfield></entry>
5879       <entry><type>text</type></entry>
5880       <entry></entry>
5881       <entry>
5882        Virtual ID of the transaction that is holding or awaiting this lock
5883       </entry>
5884      </row>
5885      <row>
5886       <entry><structfield>pid</structfield></entry>
5887       <entry><type>integer</type></entry>
5888       <entry></entry>
5889       <entry>
5890        Process ID of the server process holding or awaiting this
5891        lock.  NULL if the lock is held by a prepared transaction
5892       </entry>
5893      </row>
5894      <row>
5895       <entry><structfield>mode</structfield></entry>
5896       <entry><type>text</type></entry>
5897       <entry></entry>
5898       <entry>Name of the lock mode held or desired by this process (see <xref
5899       linkend="locking-tables">)</entry>
5900      </row>
5901      <row>
5902       <entry><structfield>granted</structfield></entry>
5903       <entry><type>boolean</type></entry>
5904       <entry></entry>
5905       <entry>True if lock is held, false if lock is awaited</entry>
5906      </row>
5907     </tbody>
5908    </tgroup>
5909   </table>
5910
5911   <para>
5912    <structfield>granted</structfield> is true in a row representing a lock
5913    held by the indicated transaction.  False indicates that this transaction is
5914    currently waiting to acquire this lock, which implies that some other
5915    transaction is holding a conflicting lock mode on the same lockable object.
5916    The waiting transaction will sleep until the other lock is released (or a
5917    deadlock situation is detected). A single transaction can be waiting to
5918    acquire at most one lock at a time.
5919   </para>
5920
5921   <para>
5922    Every transaction holds an exclusive lock on its virtual transaction ID for
5923    its entire duration.  If a permanent ID is assigned to the transaction
5924    (which normally happens only if the transaction changes the state of the
5925    database), it also holds an exclusive lock on its permanent transaction ID
5926    until it ends.  When one transaction finds it necessary to wait specifically
5927    for another transaction, it does so by attempting to acquire share lock on
5928    the other transaction ID (either virtual or permanent ID depending on the
5929    situation). That will succeed only when the other transaction
5930    terminates and releases its locks.
5931   </para>
5932
5933   <para>
5934    Although tuples are a lockable type of object,
5935    information about row-level locks is stored on disk, not in memory,
5936    and therefore row-level locks normally do not appear in this view.
5937    If a transaction is waiting for a
5938    row-level lock, it will usually appear in the view as waiting for the
5939    permanent transaction ID of the current holder of that row lock.
5940   </para>
5941
5942   <para>
5943    Advisory locks can be acquired on keys consisting of either a single
5944    <type>bigint</type> value or two integer values.  A <type>bigint</type> key is displayed with its
5945    high-order half in the <structfield>classid</> column, its low-order half
5946    in the <structfield>objid</> column, and <structfield>objsubid</> equal
5947    to 1.  Integer keys are displayed with the first key in the
5948    <structfield>classid</> column, the second key in the <structfield>objid</>
5949    column, and <structfield>objsubid</> equal to 2.  The actual meaning of
5950    the keys is up to the user.  Advisory locks are local to each database,
5951    so the <structfield>database</> column is meaningful for an advisory lock.
5952   </para>
5953
5954   <para>
5955    When the <structname>pg_locks</structname> view is accessed, the
5956    internal lock manager data structures are momentarily locked, and
5957    a copy is made for the view to display.  This ensures that the
5958    view produces a consistent set of results, while not blocking
5959    normal lock manager operations longer than necessary.  Nonetheless
5960    there could be some impact on database performance if this view is
5961    frequently accessed.
5962   </para>
5963
5964   <para>
5965    <structname>pg_locks</structname> provides a global view of all locks
5966    in the database cluster, not only those relevant to the current database.
5967    Although its <structfield>relation</structfield> column can be joined
5968    against <structname>pg_class</>.<structfield>oid</> to identify locked
5969    relations, this will only work correctly for relations in the current
5970    database (those for which the <structfield>database</structfield> column
5971    is either the current database's OID or zero).
5972   </para>
5973
5974   <para>
5975    The <structfield>pid</structfield> column can be joined to the
5976    <structfield>procpid</structfield> column of the
5977    <structname>pg_stat_activity</structname> view to get more
5978    information on the session holding or waiting to hold each lock.
5979    Also, if you are using prepared transactions, the
5980    <structfield>transaction</> column can be joined to the
5981    <structfield>transaction</structfield> column of the
5982    <structname>pg_prepared_xacts</structname> view to get more
5983    information on prepared transactions that hold locks.
5984    (A prepared transaction can never be waiting for a lock,
5985    but it continues to hold the locks it acquired while running.)
5986   </para>
5987
5988  </sect1>
5989
5990  <sect1 id="view-pg-prepared-statements">
5991   <title><structname>pg_prepared_statements</structname></title>
5992
5993   <indexterm zone="view-pg-prepared-statements">
5994    <primary>pg_prepared_statements</primary>
5995   </indexterm>
5996
5997   <para>
5998    The <structname>pg_prepared_statements</structname> view displays
5999    all the prepared statements that are available in the current
6000    session. See <xref linkend="sql-prepare"
6001    endterm="sql-prepare-title"> for more information about prepared
6002    statements.
6003   </para>
6004
6005   <para>
6006    <structname>pg_prepared_statements</structname> contains one row
6007    for each prepared statement. Rows are added to the view when a new
6008    prepared statement is created and removed when a prepared statement
6009    is released (for example, via the <xref linkend="sql-deallocate"
6010    endterm="sql-deallocate-title"> command).
6011   </para>
6012
6013   <table>
6014    <title><structname>pg_prepared_statements</> Columns</title>
6015
6016    <tgroup cols=3>
6017     <thead>
6018      <row>
6019       <entry>Name</entry>
6020       <entry>Type</entry>
6021       <entry>Description</entry>
6022      </row>
6023     </thead>
6024     <tbody>
6025      <row>
6026       <entry><structfield>name</structfield></entry>
6027       <entry><type>text</type></entry>
6028       <entry>
6029        The identifier of the prepared statement
6030       </entry>
6031      </row>
6032      <row>
6033       <entry><structfield>statement</structfield></entry>
6034       <entry><type>text</type></entry>
6035       <entry>
6036        The query string submitted by the client to create this
6037        prepared statement. For prepared statements created via SQL,
6038        this is the <command>PREPARE</command> statement submitted by
6039        the client. For prepared statements created via the
6040        frontend/backend protocol, this is the text of the prepared
6041        statement itself
6042       </entry>
6043      </row>
6044      <row>
6045       <entry><structfield>prepare_time</structfield></entry>
6046       <entry><type>timestamptz</type></entry>
6047       <entry>
6048        The time at which the prepared statement was created
6049       </entry>
6050      </row>
6051      <row>
6052       <entry><structfield>parameter_types</structfield></entry>
6053       <entry><type>regtype[]</type></entry>
6054       <entry>
6055        The expected parameter types for the prepared statement in the
6056        form of an array of <type>regtype</type>. The OID corresponding
6057        to an element of this array can be obtained by casting the
6058        <type>regtype</type> value to <type>oid</type>
6059       </entry>
6060      </row>
6061      <row>
6062       <entry><structfield>from_sql</structfield></entry>
6063       <entry><type>boolean</type></entry>
6064       <entry>
6065        <literal>true</literal> if the prepared statement was created
6066        via the <command>PREPARE</command> SQL statement;
6067        <literal>false</literal> if the statement was prepared via the
6068        frontend/backend protocol
6069       </entry>
6070      </row>
6071     </tbody>
6072    </tgroup>
6073   </table>
6074
6075   <para>
6076    The <structname>pg_prepared_statements</structname> view is read only.
6077   </para>
6078  </sect1>
6079
6080  <sect1 id="view-pg-prepared-xacts">
6081   <title><structname>pg_prepared_xacts</structname></title>
6082
6083   <indexterm zone="view-pg-prepared-xacts">
6084    <primary>pg_prepared_xacts</primary>
6085   </indexterm>
6086
6087   <para>
6088    The view <structname>pg_prepared_xacts</structname> displays
6089    information about transactions that are currently prepared for two-phase
6090    commit (see <xref linkend="sql-prepare-transaction"
6091    endterm="sql-prepare-transaction-title"> for details).
6092   </para>
6093
6094   <para>
6095    <structname>pg_prepared_xacts</structname> contains one row per prepared
6096    transaction.  An entry is removed when the transaction is committed or
6097    rolled back.
6098   </para>
6099
6100   <table>
6101    <title><structname>pg_prepared_xacts</> Columns</title>
6102
6103    <tgroup cols=4>
6104     <thead>
6105      <row>
6106       <entry>Name</entry>
6107       <entry>Type</entry>
6108       <entry>References</entry>
6109       <entry>Description</entry>
6110      </row>
6111     </thead>
6112     <tbody>
6113      <row>
6114       <entry><structfield>transaction</structfield></entry>
6115       <entry><type>xid</type></entry>
6116       <entry></entry>
6117       <entry>
6118        Numeric transaction identifier of the prepared transaction
6119       </entry>
6120      </row>
6121      <row>
6122       <entry><structfield>gid</structfield></entry>
6123       <entry><type>text</type></entry>
6124       <entry></entry>
6125       <entry>
6126        Global transaction identifier that was assigned to the transaction
6127       </entry>
6128      </row>
6129      <row>
6130       <entry><structfield>prepared</structfield></entry>
6131       <entry><type>timestamp with time zone</type></entry>
6132       <entry></entry>
6133       <entry>
6134        Time at which the transaction was prepared for commit
6135       </entry>
6136      </row>
6137      <row>
6138       <entry><structfield>owner</structfield></entry>
6139       <entry><type>name</type></entry>
6140       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.rolname</literal></entry>
6141       <entry>
6142        Name of the user that executed the transaction
6143       </entry>
6144      </row>
6145      <row>
6146       <entry><structfield>database</structfield></entry>
6147       <entry><type>name</type></entry>
6148       <entry><literal><link linkend="catalog-pg-database"><structname>pg_database</structname></link>.datname</literal></entry>
6149       <entry>
6150        Name of the database in which the transaction was executed
6151       </entry>
6152      </row>
6153     </tbody>
6154    </tgroup>
6155   </table>
6156
6157   <para>
6158    When the <structname>pg_prepared_xacts</structname> view is accessed, the
6159    internal transaction manager data structures are momentarily locked, and
6160    a copy is made for the view to display.  This ensures that the
6161    view produces a consistent set of results, while not blocking
6162    normal operations longer than necessary.  Nonetheless
6163    there could be some impact on database performance if this view is
6164    frequently accessed.
6165   </para>
6166
6167  </sect1>
6168
6169  <sect1 id="view-pg-roles">
6170   <title><structname>pg_roles</structname></title>
6171
6172   <indexterm zone="view-pg-roles">
6173    <primary>pg_roles</primary>
6174   </indexterm>
6175
6176   <para>
6177    The view <structname>pg_roles</structname> provides access to
6178    information about database roles.  This is simply a publicly
6179    readable view of
6180    <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>
6181    that blanks out the password field.
6182   </para>
6183
6184   <para>
6185    This view explicitly exposes the OID column of the underlying table,
6186    since that is needed to do joins to other catalogs.
6187   </para>
6188
6189   <table>
6190    <title><structname>pg_roles</> Columns</title>
6191
6192    <tgroup cols=4>
6193     <thead>
6194      <row>
6195       <entry>Name</entry>
6196       <entry>Type</entry>
6197       <entry>References</entry>
6198       <entry>Description</entry>
6199      </row>
6200     </thead>
6201
6202     <tbody>
6203      <row>
6204       <entry><structfield>rolname</structfield></entry>
6205       <entry><type>name</type></entry>
6206       <entry></entry>
6207       <entry>Role name</entry>
6208      </row>
6209
6210      <row>
6211       <entry><structfield>rolsuper</structfield></entry>
6212       <entry><type>bool</type></entry>
6213       <entry></entry>
6214       <entry>Role has superuser privileges</entry>
6215      </row>
6216
6217      <row>
6218       <entry><structfield>rolinherit</structfield></entry>
6219       <entry><type>bool</type></entry>
6220       <entry></entry>
6221       <entry>Role automatically inherits privileges of roles it is a
6222        member of</entry>
6223      </row>
6224
6225      <row>
6226       <entry><structfield>rolcreaterole</structfield></entry>
6227       <entry><type>bool</type></entry>
6228       <entry></entry>
6229       <entry>Role can create more roles</entry>
6230      </row>
6231
6232      <row>
6233       <entry><structfield>rolcreatedb</structfield></entry>
6234       <entry><type>bool</type></entry>
6235       <entry></entry>
6236       <entry>Role can create databases</entry>
6237      </row>
6238
6239      <row>
6240       <entry><structfield>rolcatupdate</structfield></entry>
6241       <entry><type>bool</type></entry>
6242       <entry></entry>
6243       <entry>
6244        Role can update system catalogs directly.  (Even a superuser cannot do
6245        this unless this column is true.)
6246       </entry>
6247      </row>
6248
6249      <row>
6250       <entry><structfield>rolcanlogin</structfield></entry>
6251       <entry><type>bool</type></entry>
6252       <entry></entry>
6253       <entry>
6254        Role can log in. That is, this role can be given as the initial
6255        session authorization identifier
6256       </entry>
6257      </row>
6258
6259      <row>
6260       <entry><structfield>rolconnlimit</structfield></entry>
6261       <entry><type>int4</type></entry>
6262       <entry></entry>
6263       <entry>
6264        For roles that can log in, this sets maximum number of concurrent
6265        connections this role can make.  -1 means no limit
6266       </entry>
6267      </row>
6268
6269      <row>
6270       <entry><structfield>rolpassword</structfield></entry>
6271       <entry><type>text</type></entry>
6272       <entry></entry>
6273       <entry>Not the password (always reads as <literal>********</>)</entry>
6274      </row>
6275
6276      <row>
6277       <entry><structfield>rolvaliduntil</structfield></entry>
6278       <entry><type>timestamptz</type></entry>
6279       <entry></entry>
6280       <entry>Password expiry time (only used for password authentication);
6281        NULL if no expiration</entry>
6282      </row>
6283
6284      <row>
6285       <entry><structfield>rolconfig</structfield></entry>
6286       <entry><type>text[]</type></entry>
6287       <entry></entry>
6288       <entry>Session defaults for run-time configuration variables</entry>
6289      </row>
6290
6291      <row>
6292       <entry><structfield>oid</structfield></entry>
6293       <entry><type>oid</type></entry>
6294       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
6295       <entry>ID of role</entry>
6296      </row>
6297     </tbody>
6298    </tgroup>
6299   </table>
6300
6301  </sect1>
6302
6303  <sect1 id="view-pg-rules">
6304   <title><structname>pg_rules</structname></title>
6305
6306   <indexterm zone="view-pg-rules">
6307    <primary>pg_rules</primary>
6308   </indexterm>
6309
6310   <para>
6311    The view <structname>pg_rules</structname> provides access to
6312    useful information about query rewrite rules.
6313   </para>
6314
6315   <table>
6316    <title><structname>pg_rules</> Columns</title>
6317
6318    <tgroup cols=4>
6319     <thead>
6320      <row>
6321       <entry>Name</entry>
6322       <entry>Type</entry>
6323       <entry>References</entry>
6324       <entry>Description</entry>
6325      </row>
6326     </thead>
6327     <tbody>
6328      <row>
6329       <entry><structfield>schemaname</structfield></entry>
6330       <entry><type>name</type></entry>
6331       <entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.nspname</literal></entry>
6332       <entry>Name of schema containing table</entry>
6333      </row>
6334      <row>
6335       <entry><structfield>tablename</structfield></entry>
6336       <entry><type>name</type></entry>
6337       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.relname</literal></entry>
6338       <entry>Name of table the rule is for</entry>
6339      </row>
6340      <row>
6341       <entry><structfield>rulename</structfield></entry>
6342       <entry><type>name</type></entry>
6343       <entry><literal><link linkend="catalog-pg-rewrite"><structname>pg_rewrite</structname></link>.rulename</literal></entry>
6344       <entry>Name of rule</entry>
6345      </row>
6346      <row>
6347       <entry><structfield>definition</structfield></entry>
6348       <entry><type>text</type></entry>
6349       <entry></entry>
6350       <entry>Rule definition (a reconstructed creation command)</entry>
6351      </row>
6352     </tbody>
6353    </tgroup>
6354   </table>
6355
6356   <para>
6357    The <structname>pg_rules</> view excludes the <literal>ON SELECT</> rules
6358    of views; those can be seen in <structname>pg_views</>.
6359   </para>
6360
6361  </sect1>
6362
6363  <sect1 id="view-pg-settings">
6364   <title><structname>pg_settings</structname></title>
6365
6366   <indexterm zone="view-pg-settings">
6367    <primary>pg_settings</primary>
6368   </indexterm>
6369
6370   <para>
6371    The view <structname>pg_settings</structname> provides access to
6372    run-time parameters of the server.  It is essentially an alternative
6373    interface to the <xref linkend="sql-show" endterm="sql-show-title">
6374    and <xref linkend="sql-set" endterm="sql-set-title"> commands.
6375    It also provides access to some facts about each parameter that are
6376    not directly available from <command>SHOW</>, such as minimum and
6377    maximum values.
6378   </para>
6379
6380   <table>
6381    <title><structname>pg_settings</> Columns</title>
6382
6383    <tgroup cols=3>
6384     <thead>
6385      <row>
6386       <entry>Name</entry>
6387       <entry>Type</entry>
6388       <entry>Description</entry>
6389      </row>
6390     </thead>
6391     <tbody>
6392      <row>
6393       <entry><structfield>name</structfield></entry>
6394       <entry><type>text</type></entry>
6395       <entry>Run-time configuration parameter name</entry>
6396      </row>
6397      <row>
6398       <entry><structfield>setting</structfield></entry>
6399       <entry><type>text</type></entry>
6400       <entry>Current value of the parameter</entry>
6401      </row>
6402      <row>
6403       <entry><structfield>unit</structfield></entry>
6404       <entry><type>text</type></entry>
6405       <entry>Implicit unit of the parameter</entry>
6406      </row>
6407      <row>
6408       <entry><structfield>category</structfield></entry>
6409       <entry><type>text</type></entry>
6410       <entry>Logical group of the parameter</entry>
6411      </row>
6412      <row>
6413       <entry><structfield>short_desc</structfield></entry>
6414       <entry><type>text</type></entry>
6415       <entry>A brief description of the parameter</entry>
6416      </row>
6417      <row>
6418       <entry><structfield>extra_desc</structfield></entry>
6419       <entry><type>text</type></entry>
6420       <entry>Additional, more detailed, description of the parameter</entry>
6421      </row>
6422      <row>
6423       <entry><structfield>context</structfield></entry>
6424       <entry><type>text</type></entry>
6425       <entry>Context required to set the parameter's value</entry>
6426      </row>
6427      <row>
6428       <entry><structfield>vartype</structfield></entry>
6429       <entry><type>text</type></entry>
6430       <entry>Parameter type (<literal>bool</>, <literal>enum</>,
6431        <literal>integer</>, <literal>real</>, or <literal>string</>)
6432       </entry>
6433      </row>
6434      <row>
6435       <entry><structfield>source</structfield></entry>
6436       <entry><type>text</type></entry>
6437       <entry>Source of the current parameter value</entry>
6438      </row>
6439      <row>
6440       <entry><structfield>min_val</structfield></entry>
6441       <entry><type>text</type></entry>
6442       <entry>Minimum allowed value of the parameter (NULL for non-numeric
6443       values)</entry>
6444      </row>
6445      <row>
6446       <entry><structfield>max_val</structfield></entry>
6447       <entry><type>text</type></entry>
6448       <entry>Maximum allowed value of the parameter (NULL for non-numeric
6449       values)</entry>
6450      </row>
6451      <row>
6452       <entry><structfield>enumvals</structfield></entry>
6453       <entry><type>text</type></entry>
6454       <entry>Allowed values of an enum parameter (NULL for non-enum
6455       values)</entry>
6456      </row>
6457      <row>
6458       <entry><structfield>boot_val</structfield></entry>
6459       <entry><type>text</type></entry>
6460       <entry>Parameter value assumed at server startup if the parameter is
6461       not otherwise set</entry>
6462      </row>
6463      <row>
6464       <entry><structfield>reset_val</structfield></entry>
6465       <entry><type>text</type></entry>
6466       <entry>Value that <command>RESET</command> would reset the parameter to
6467       in the current session</entry>
6468      </row>
6469      <row>
6470       <entry><structfield>sourcefile</structfield></entry>
6471       <entry><type>text</type></entry>
6472       <entry>Configuration file the current value was set in (NULL for
6473       values set from sources other than configuration files, or when
6474       examined by a non-superuser).
6475       Helpful when using configuration include directives</entry>
6476      </row>
6477      <row>
6478       <entry><structfield>sourceline</structfield></entry>
6479       <entry><type>integer</type></entry>
6480       <entry>Line number within the configuration file the current value was
6481       set at (NULL for values set from sources other than configuration files,
6482       or when examined by a non-superuser)
6483       </entry>
6484      </row>
6485     </tbody>
6486    </tgroup>
6487   </table>
6488
6489   <para>
6490    The <structname>pg_settings</structname> view cannot be inserted into or
6491    deleted from, but it can be updated.  An <command>UPDATE</command> applied
6492    to a row of <structname>pg_settings</structname> is equivalent to executing
6493    the <xref linkend="sql-set" endterm="sql-set-title"> command on that named
6494    parameter. The change only affects the value used by the current
6495    session. If an <command>UPDATE</command> is issued within a transaction
6496    that is later aborted, the effects of the <command>UPDATE</command> command
6497    disappear when the transaction is rolled back. Once the surrounding
6498    transaction is committed, the effects will persist until the end of the
6499    session, unless overridden by another <command>UPDATE</command> or
6500    <command>SET</command>.
6501   </para>
6502
6503  </sect1>
6504
6505  <sect1 id="view-pg-shadow">
6506   <title><structname>pg_shadow</structname></title>
6507
6508   <indexterm zone="view-pg-shadow">
6509    <primary>pg_shadow</primary>
6510   </indexterm>
6511
6512   <para>
6513    The view <structname>pg_shadow</structname> exists for backwards
6514    compatibility: it emulates a catalog that existed in
6515    <productname>PostgreSQL</productname> before version 8.1.
6516    It shows properties of all roles that are marked as
6517    <structfield>rolcanlogin</>.
6518   </para>
6519
6520   <para>
6521    The name stems from the fact that this table
6522    should not be readable by the public since it contains passwords.
6523    <link linkend="view-pg-user"><structname>pg_user</structname></link>
6524    is a publicly readable view on
6525    <structname>pg_shadow</structname> that blanks out the password field.
6526   </para>
6527
6528   <table>
6529    <title><structname>pg_shadow</> Columns</title>
6530
6531    <tgroup cols=4>
6532     <thead>
6533      <row>
6534       <entry>Name</entry>
6535       <entry>Type</entry>
6536       <entry>References</entry>
6537       <entry>Description</entry>
6538      </row>
6539     </thead>
6540
6541     <tbody>
6542      <row>
6543       <entry><structfield>usename</structfield></entry>
6544       <entry><type>name</type></entry>
6545       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.rolname</literal></entry>
6546       <entry>User name</entry>
6547      </row>
6548
6549      <row>
6550       <entry><structfield>usesysid</structfield></entry>
6551       <entry><type>oid</type></entry>
6552       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
6553       <entry>ID of this user</entry>
6554      </row>
6555
6556      <row>
6557       <entry><structfield>usecreatedb</structfield></entry>
6558       <entry><type>bool</type></entry>
6559       <entry></entry>
6560       <entry>User can create databases</entry>
6561      </row>
6562
6563      <row>
6564       <entry><structfield>usesuper</structfield></entry>
6565       <entry><type>bool</type></entry>
6566       <entry></entry>
6567       <entry>User is a superuser</entry>
6568      </row>
6569
6570      <row>
6571       <entry><structfield>usecatupd</structfield></entry>
6572       <entry><type>bool</type></entry>
6573       <entry></entry>
6574       <entry>
6575        User can update system catalogs.  (Even a superuser cannot do
6576        this unless this column is true.)
6577       </entry>
6578      </row>
6579
6580      <row>
6581       <entry><structfield>passwd</structfield></entry>
6582       <entry><type>text</type></entry>
6583       <entry></entry>
6584       <entry>Password (possibly encrypted)</entry>
6585      </row>
6586
6587      <row>
6588       <entry><structfield>valuntil</structfield></entry>
6589       <entry><type>abstime</type></entry>
6590       <entry></entry>
6591       <entry>Password expiry time (only used for password authentication)</entry>
6592      </row>
6593
6594      <row>
6595       <entry><structfield>useconfig</structfield></entry>
6596       <entry><type>text[]</type></entry>
6597       <entry></entry>
6598       <entry>Session defaults for run-time configuration variables</entry>
6599      </row>
6600     </tbody>
6601    </tgroup>
6602   </table>
6603
6604  </sect1>
6605
6606  <sect1 id="view-pg-stats">
6607   <title><structname>pg_stats</structname></title>
6608
6609   <indexterm zone="view-pg-stats">
6610    <primary>pg_stats</primary>
6611   </indexterm>
6612
6613   <para>
6614    The view <structname>pg_stats</structname> provides access to
6615    the information stored in the <link
6616    linkend="catalog-pg-statistic"><structname>pg_statistic</structname></link>
6617    catalog.  This view allows access only to rows of
6618    <structname>pg_statistic</structname> that correspond to tables the
6619    user has permission to read, and therefore it is safe to allow public
6620    read access to this view.
6621   </para>
6622
6623   <para>
6624    <structname>pg_stats</structname> is also designed to present the
6625    information in a more readable format than the underlying catalog
6626    &mdash; at the cost that its schema must be extended whenever new slot types
6627    are defined for <structname>pg_statistic</structname>.
6628   </para>
6629
6630   <table>
6631    <title><structname>pg_stats</> Columns</title>
6632
6633    <tgroup cols=4>
6634     <thead>
6635      <row>
6636       <entry>Name</entry>
6637       <entry>Type</entry>
6638       <entry>References</entry>
6639       <entry>Description</entry>
6640      </row>
6641     </thead>
6642     <tbody>
6643      <row>
6644       <entry><structfield>schemaname</structfield></entry>
6645       <entry><type>name</type></entry>
6646       <entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.nspname</literal></entry>
6647       <entry>Name of schema containing table</entry>
6648      </row>
6649
6650      <row>
6651       <entry><structfield>tablename</structfield></entry>
6652       <entry><type>name</type></entry>
6653       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.relname</literal></entry>
6654       <entry>Name of table</entry>
6655      </row>
6656
6657      <row>
6658       <entry><structfield>attname</structfield></entry>
6659       <entry><type>name</type></entry>
6660       <entry><literal><link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link>.attname</literal></entry>
6661       <entry>Name of the column described by this row</entry>
6662      </row>
6663
6664      <row>
6665       <entry><structfield>null_frac</structfield></entry>
6666       <entry><type>real</type></entry>
6667       <entry></entry>
6668       <entry>Fraction of column entries that are null</entry>
6669      </row>
6670
6671      <row>
6672       <entry><structfield>avg_width</structfield></entry>
6673       <entry><type>integer</type></entry>
6674       <entry></entry>
6675       <entry>Average width in bytes of column's entries</entry>
6676      </row>
6677
6678      <row>
6679       <entry><structfield>n_distinct</structfield></entry>
6680       <entry><type>real</type></entry>
6681       <entry></entry>
6682       <entry>
6683        If greater than zero, the estimated number of distinct values in the
6684        column.  If less than zero, the negative of the number of distinct
6685        values divided by the number of rows.  (The negated form is used when
6686        <command>ANALYZE</> believes that the number of distinct values is
6687        likely to increase as the table grows; the positive form is used when
6688        the column seems to have a fixed number of possible values.)  For
6689        example, -1 indicates a unique column in which the number of distinct
6690        values is the same as the number of rows
6691       </entry>
6692      </row>
6693
6694      <row>
6695       <entry><structfield>most_common_vals</structfield></entry>
6696       <entry><type>anyarray</type></entry>
6697       <entry></entry>
6698       <entry>
6699        A list of the most common values in the column. (NULL if
6700        no values seem to be more common than any others.)
6701        For some datatypes such as <type>tsvector</>, this is a list of
6702        the most common element values rather than values of the type itself.
6703       </entry>
6704      </row>
6705
6706      <row>
6707       <entry><structfield>most_common_freqs</structfield></entry>
6708       <entry><type>real[]</type></entry>
6709       <entry></entry>
6710       <entry>
6711        A list of the frequencies of the most common values or elements,
6712        i.e., number of occurrences of each divided by total number of rows.
6713        (NULL when <structfield>most_common_vals</structfield> is.)
6714        For some datatypes such as <type>tsvector</>, it can also store some
6715        additional information, making it longer than the
6716        <structfield>most_common_vals</> array.
6717       </entry>
6718      </row>
6719
6720      <row>
6721       <entry><structfield>histogram_bounds</structfield></entry>
6722       <entry><type>anyarray</type></entry>
6723       <entry></entry>
6724       <entry>
6725        A list of values that divide the column's values into groups of
6726        approximately equal population.  The values in
6727        <structfield>most_common_vals</>, if present, are omitted from this
6728        histogram calculation.  (This column is NULL if the column data type
6729        does not have a <literal>&lt;</> operator or if the
6730        <structfield>most_common_vals</> list accounts for the entire
6731        population.)
6732       </entry>
6733      </row>
6734
6735      <row>
6736       <entry><structfield>correlation</structfield></entry>
6737       <entry><type>real</type></entry>
6738       <entry></entry>
6739       <entry>
6740        Statistical correlation between physical row ordering and
6741        logical ordering of the column values.  This ranges from -1 to +1.
6742        When the value is near -1 or +1, an index scan on the column will
6743        be estimated to be cheaper than when it is near zero, due to reduction
6744        of random access to the disk.  (This column is NULL if the column data
6745        type does not have a <literal>&lt;</> operator.)
6746       </entry>
6747      </row>
6748     </tbody>
6749    </tgroup>
6750   </table>
6751
6752   <para>
6753    The maximum number of entries in the <structfield>most_common_vals</>
6754    and <structfield>histogram_bounds</> arrays can be set on a
6755    column-by-column basis using the <command>ALTER TABLE SET STATISTICS</>
6756    command, or globally by setting the
6757    <xref linkend="guc-default-statistics-target"> run-time parameter.
6758   </para>
6759
6760  </sect1>
6761
6762  <sect1 id="view-pg-tables">
6763   <title><structname>pg_tables</structname></title>
6764
6765   <indexterm zone="view-pg-tables">
6766    <primary>pg_tables</primary>
6767   </indexterm>
6768
6769   <para>
6770    The view <structname>pg_tables</structname> provides access to
6771    useful information about each table in the database.
6772   </para>
6773
6774   <table>
6775    <title><structname>pg_tables</> Columns</title>
6776
6777    <tgroup cols=4>
6778     <thead>
6779      <row>
6780       <entry>Name</entry>
6781       <entry>Type</entry>
6782       <entry>References</entry>
6783       <entry>Description</entry>
6784      </row>
6785     </thead>
6786     <tbody>
6787      <row>
6788       <entry><structfield>schemaname</structfield></entry>
6789       <entry><type>name</type></entry>
6790       <entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.nspname</literal></entry>
6791       <entry>Name of schema containing table</entry>
6792      </row>
6793      <row>
6794       <entry><structfield>tablename</structfield></entry>
6795       <entry><type>name</type></entry>
6796       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.relname</literal></entry>
6797       <entry>Name of table</entry>
6798      </row>
6799      <row>
6800       <entry><structfield>tableowner</structfield></entry>
6801       <entry><type>name</type></entry>
6802       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.rolname</literal></entry>
6803       <entry>Name of table's owner</entry>
6804      </row>
6805      <row>
6806       <entry><structfield>tablespace</structfield></entry>
6807       <entry><type>name</type></entry>
6808       <entry><literal><link linkend="catalog-pg-tablespace"><structname>pg_tablespace</structname></link>.spcname</literal></entry>
6809       <entry>Name of tablespace containing table (NULL if default for database)</entry>
6810      </row>
6811      <row>
6812       <entry><structfield>hasindexes</structfield></entry>
6813       <entry><type>boolean</type></entry>
6814       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.relhasindex</literal></entry>
6815       <entry>true if table has (or recently had) any indexes</entry>
6816      </row>
6817      <row>
6818       <entry><structfield>hasrules</structfield></entry>
6819       <entry><type>boolean</type></entry>
6820       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.relhasrules</literal></entry>
6821       <entry>true if table has rules</entry>
6822      </row>
6823      <row>
6824       <entry><structfield>hastriggers</structfield></entry>
6825       <entry><type>boolean</type></entry>
6826       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.reltriggers</literal></entry>
6827       <entry>true if table has triggers</entry>
6828      </row>
6829     </tbody>
6830    </tgroup>
6831   </table>
6832
6833  </sect1>
6834
6835  <sect1 id="view-pg-timezone-abbrevs">
6836   <title><structname>pg_timezone_abbrevs</structname></title>
6837
6838   <indexterm zone="view-pg-timezone-abbrevs">
6839    <primary>pg_timezone_abbrevs</primary>
6840   </indexterm>
6841
6842   <para>
6843    The view <structname>pg_timezone_abbrevs</structname> provides a list
6844    of time zone abbreviations that are currently recognized by the datetime
6845    input routines.  The contents of this view change when the
6846    <xref linkend="guc-timezone-abbreviations"> run-time parameter is modified.
6847   </para>
6848
6849   <table>
6850    <title><structname>pg_timezone_abbrevs</> Columns</title>
6851
6852    <tgroup cols=3>
6853     <thead>
6854      <row>
6855       <entry>Name</entry>
6856       <entry>Type</entry>
6857       <entry>Description</entry>
6858      </row>
6859     </thead>
6860     <tbody>
6861      <row>
6862       <entry><structfield>abbrev</structfield></entry>
6863       <entry><type>text</type></entry>
6864       <entry>Time zone abbreviation</entry>
6865      </row>
6866      <row>
6867       <entry><structfield>utc_offset</structfield></entry>
6868       <entry><type>interval</type></entry>
6869       <entry>Offset from UTC (positive means east of Greenwich)</entry>
6870      </row>
6871      <row>
6872       <entry><structfield>is_dst</structfield></entry>
6873       <entry><type>boolean</type></entry>
6874       <entry>True if this is a daylight-savings abbreviation</entry>
6875      </row>
6876     </tbody>
6877    </tgroup>
6878   </table>
6879
6880  </sect1>
6881
6882  <sect1 id="view-pg-timezone-names">
6883   <title><structname>pg_timezone_names</structname></title>
6884
6885   <indexterm zone="view-pg-timezone-names">
6886    <primary>pg_timezone_names</primary>
6887   </indexterm>
6888
6889   <para>
6890    The view <structname>pg_timezone_names</structname> provides a list
6891    of time zone names that are recognized by <command>SET TIMEZONE</>,
6892    along with their associated abbreviations, UTC offsets,
6893    and daylight-savings status.
6894    Unlike the abbreviations shown in <link
6895    linkend="view-pg-timezone-abbrevs"><structname>pg_timezone_abbrevs</structname></link>, many of these names imply a set of daylight-savings transition
6896    date rules.  Therefore, the associated information changes across local DST
6897    boundaries.  The displayed information is computed based on the current
6898    value of <function>CURRENT_TIMESTAMP</>.
6899   </para>
6900
6901   <table>
6902    <title><structname>pg_timezone_names</> Columns</title>
6903
6904    <tgroup cols=3>
6905     <thead>
6906      <row>
6907       <entry>Name</entry>
6908       <entry>Type</entry>
6909       <entry>Description</entry>
6910      </row>
6911     </thead>
6912     <tbody>
6913      <row>
6914       <entry><structfield>name</structfield></entry>
6915       <entry><type>text</type></entry>
6916       <entry>Time zone name</entry>
6917      </row>
6918      <row>
6919       <entry><structfield>abbrev</structfield></entry>
6920       <entry><type>text</type></entry>
6921       <entry>Time zone abbreviation</entry>
6922      </row>
6923      <row>
6924       <entry><structfield>utc_offset</structfield></entry>
6925       <entry><type>interval</type></entry>
6926       <entry>Offset from UTC (positive means east of Greenwich)</entry>
6927      </row>
6928      <row>
6929       <entry><structfield>is_dst</structfield></entry>
6930       <entry><type>boolean</type></entry>
6931       <entry>True if currently observing daylight savings</entry>
6932      </row>
6933     </tbody>
6934    </tgroup>
6935   </table>
6936
6937  </sect1>
6938
6939  <sect1 id="view-pg-user">
6940   <title><structname>pg_user</structname></title>
6941
6942   <indexterm zone="view-pg-user">
6943    <primary>pg_user</primary>
6944   </indexterm>
6945
6946   <para>
6947    The view <structname>pg_user</structname> provides access to
6948    information about database users.  This is simply a publicly
6949    readable view of
6950    <link linkend="view-pg-shadow"><structname>pg_shadow</structname></link>
6951    that blanks out the password field.
6952   </para>
6953
6954   <table>
6955    <title><structname>pg_user</> Columns</title>
6956
6957    <tgroup cols=3>
6958     <thead>
6959      <row>
6960       <entry>Name</entry>
6961       <entry>Type</entry>
6962       <entry>Description</entry>
6963      </row>
6964     </thead>
6965     <tbody>
6966      <row>
6967       <entry><structfield>usename</structfield></entry>
6968       <entry><type>name</type></entry>
6969       <entry>User name</entry>
6970      </row>
6971
6972      <row>
6973       <entry><structfield>usesysid</structfield></entry>
6974       <entry><type>int4</type></entry>
6975       <entry>User ID (arbitrary number used to reference this user)</entry>
6976      </row>
6977
6978      <row>
6979       <entry><structfield>usecreatedb</structfield></entry>
6980       <entry><type>bool</type></entry>
6981       <entry>User can create databases</entry>
6982      </row>
6983
6984      <row>
6985       <entry><structfield>usesuper</structfield></entry>
6986       <entry><type>bool</type></entry>
6987       <entry>User is a superuser</entry>
6988      </row>
6989
6990      <row>
6991       <entry><structfield>usecatupd</structfield></entry>
6992       <entry><type>bool</type></entry>
6993       <entry>
6994        User can update system catalogs.  (Even a superuser cannot do
6995        this unless this column is true.)
6996       </entry>
6997      </row>
6998
6999      <row>
7000       <entry><structfield>passwd</structfield></entry>
7001       <entry><type>text</type></entry>
7002       <entry>Not the password (always reads as <literal>********</>)</entry>
7003      </row>
7004
7005      <row>
7006       <entry><structfield>valuntil</structfield></entry>
7007       <entry><type>abstime</type></entry>
7008       <entry>Password expiry time (only used for password authentication)</entry>
7009      </row>
7010
7011      <row>
7012       <entry><structfield>useconfig</structfield></entry>
7013       <entry><type>text[]</type></entry>
7014       <entry>Session defaults for run-time configuration variables</entry>
7015      </row>
7016     </tbody>
7017    </tgroup>
7018   </table>
7019
7020  </sect1>
7021
7022  <sect1 id="view-pg-views">
7023   <title><structname>pg_views</structname></title>
7024
7025   <indexterm zone="view-pg-views">
7026    <primary>pg_views</primary>
7027   </indexterm>
7028
7029   <para>
7030    The view <structname>pg_views</structname> provides access to
7031    useful information about each view in the database.
7032   </para>
7033
7034   <table>
7035    <title><structname>pg_views</> Columns</title>
7036
7037    <tgroup cols=4>
7038     <thead>
7039      <row>
7040       <entry>Name</entry>
7041       <entry>Type</entry>
7042       <entry>References</entry>
7043       <entry>Description</entry>
7044      </row>
7045     </thead>
7046     <tbody>
7047      <row>
7048       <entry><structfield>schemaname</structfield></entry>
7049       <entry><type>name</type></entry>
7050       <entry><literal><link linkend="catalog-pg-namespace"><structname>pg_namespace</structname></link>.nspname</literal></entry>
7051       <entry>Name of schema containing view</entry>
7052      </row>
7053      <row>
7054       <entry><structfield>viewname</structfield></entry>
7055       <entry><type>name</type></entry>
7056       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.relname</literal></entry>
7057       <entry>Name of view</entry>
7058      </row>
7059      <row>
7060       <entry><structfield>viewowner</structfield></entry>
7061       <entry><type>name</type></entry>
7062       <entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.rolname</literal></entry>
7063       <entry>Name of view's owner</entry>
7064      </row>
7065      <row>
7066       <entry><structfield>definition</structfield></entry>
7067       <entry><type>text</type></entry>
7068       <entry></entry>
7069       <entry>View definition (a reconstructed <command>SELECT</command> query)</entry>
7070      </row>
7071     </tbody>
7072    </tgroup>
7073   </table>
7074
7075  </sect1>
7076
7077 </chapter>