src/include/storage/relfilelocator.h

   1 /*-------------------------------------------------------------------------
   2  *
   3  * relfilelocator.h
   4  *        Physical access information for relations.
   5  *
   6  *
   7  * Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
   8  * Portions Copyright (c) 1994, Regents of the University of California
   9  *
  10  * src/include/storage/relfilelocator.h
  11  *
  12  *-------------------------------------------------------------------------
  13  */
  14 #ifndef RELFILELOCATOR_H
  15 #define RELFILELOCATOR_H
  16
  17 #include "common/relpath.h"
  18 #include "storage/procnumber.h"
  19
  20 /*
  21  * RelFileLocator must provide all that we need to know to physically access
  22  * a relation, with the exception of the backend's proc number, which can be
  23  * provided separately.  Note, however, that a "physical" relation is
  24  * comprised of multiple files on the filesystem, as each fork is stored as
  25  * a separate file, and each fork can be divided into multiple segments. See
  26  * md.c.
  27  *
  28  * spcOid identifies the tablespace of the relation.  It corresponds to
  29  * pg_tablespace.oid.
  30  *
  31  * dbOid identifies the database of the relation.  It is zero for
  32  * "shared" relations (those common to all databases of a cluster).
  33  * Nonzero dbOid values correspond to pg_database.oid.
  34  *
  35  * relNumber identifies the specific relation.  relNumber corresponds to
  36  * pg_class.relfilenode (NOT pg_class.oid, because we need to be able
  37  * to assign new physical files to relations in some situations).
  38  * Notice that relNumber is only unique within a database in a particular
  39  * tablespace.
  40  *
  41  * Note: spcOid must be GLOBALTABLESPACE_OID if and only if dbOid is
  42  * zero.  We support shared relations only in the "global" tablespace.
  43  *
  44  * Note: in pg_class we allow reltablespace == 0 to denote that the
  45  * relation is stored in its database's "default" tablespace (as
  46  * identified by pg_database.dattablespace).  However this shorthand
  47  * is NOT allowed in RelFileLocator structs --- the real tablespace ID
  48  * must be supplied when setting spcOid.
  49  *
  50  * Note: in pg_class, relfilenode can be zero to denote that the relation
  51  * is a "mapped" relation, whose current true filenode number is available
  52  * from relmapper.c.  Again, this case is NOT allowed in RelFileLocators.
  53  *
  54  * Note: various places use RelFileLocator in hashtable keys.  Therefore,
  55  * there *must not* be any unused padding bytes in this struct.  That
  56  * should be safe as long as all the fields are of type Oid.
  57  */
  58 typedef struct RelFileLocator
  59 {
  60         Oid                     spcOid;                 /* tablespace */
  61         Oid                     dbOid;                  /* database */
  62         RelFileNumber relNumber;        /* relation */
  63 } RelFileLocator;
  64
  65 /*
  66  * Augmenting a relfilelocator with the backend's proc number provides all the
  67  * information we need to locate the physical storage.  'backend' is
  68  * INVALID_PROC_NUMBER for regular relations (those accessible to more than
  69  * one backend), or the owning backend's proc number for backend-local
  70  * relations.  Backend-local relations are always transient and removed in
  71  * case of a database crash; they are never WAL-logged or fsync'd.
  72  */
  73 typedef struct RelFileLocatorBackend
  74 {
  75         RelFileLocator locator;
  76         ProcNumber      backend;
  77 } RelFileLocatorBackend;
  78
  79 #define RelFileLocatorBackendIsTemp(rlocator) \
  80         ((rlocator).backend != INVALID_PROC_NUMBER)
  81
  82 /*
  83  * Note: RelFileLocatorEquals and RelFileLocatorBackendEquals compare relNumber
  84  * first since that is most likely to be different in two unequal
  85  * RelFileLocators.  It is probably redundant to compare spcOid if the other
  86  * fields are found equal, but do it anyway to be sure.  Likewise for checking
  87  * the backend number in RelFileLocatorBackendEquals.
  88  */
  89 #define RelFileLocatorEquals(locator1, locator2) \
  90         ((locator1).relNumber == (locator2).relNumber && \
  91          (locator1).dbOid == (locator2).dbOid && \
  92          (locator1).spcOid == (locator2).spcOid)
  93
  94 #define RelFileLocatorBackendEquals(locator1, locator2) \
  95         ((locator1).locator.relNumber == (locator2).locator.relNumber && \
  96          (locator1).locator.dbOid == (locator2).locator.dbOid && \
  97          (locator1).backend == (locator2).backend && \
  98          (locator1).locator.spcOid == (locator2).locator.spcOid)
  99
 100 #endif                                                  /* RELFILELOCATOR_H */