src/include/access/transam.h

   1 /*-------------------------------------------------------------------------
   2  *
   3  * transam.h
   4  *        postgres transaction access method support code
   5  *
   6  *
   7  * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
   8  * Portions Copyright (c) 1994, Regents of the University of California
   9  *
  10  * src/include/access/transam.h
  11  *
  12  *-------------------------------------------------------------------------
  13  */
  14 #ifndef TRANSAM_H
  15 #define TRANSAM_H
  16
  17 #include "access/xlogdefs.h"
  18
  19
  20 /* ----------------
  21  *              Special transaction ID values
  22  *
  23  * BootstrapTransactionId is the XID for "bootstrap" operations, and
  24  * FrozenTransactionId is used for very old tuples.  Both should
  25  * always be considered valid.
  26  *
  27  * FirstNormalTransactionId is the first "normal" transaction id.
  28  * Note: if you need to change it, you must change pg_class.h as well.
  29  * ----------------
  30  */
  31 #define InvalidTransactionId            ((TransactionId) 0)
  32 #define BootstrapTransactionId          ((TransactionId) 1)
  33 #define FrozenTransactionId                     ((TransactionId) 2)
  34 #define FirstNormalTransactionId        ((TransactionId) 3)
  35 #define MaxTransactionId                        ((TransactionId) 0xFFFFFFFF)
  36
  37 /* ----------------
  38  *              transaction ID manipulation macros
  39  * ----------------
  40  */
  41 #define TransactionIdIsValid(xid)               ((xid) != InvalidTransactionId)
  42 #define TransactionIdIsNormal(xid)              ((xid) >= FirstNormalTransactionId)
  43 #define TransactionIdEquals(id1, id2)   ((id1) == (id2))
  44 #define TransactionIdStore(xid, dest)   (*(dest) = (xid))
  45 #define StoreInvalidTransactionId(dest) (*(dest) = InvalidTransactionId)
  46
  47 #define EpochFromFullTransactionId(x)   ((uint32) ((x).value >> 32))
  48 #define XidFromFullTransactionId(x)             ((uint32) (x).value)
  49 #define U64FromFullTransactionId(x)             ((x).value)
  50 #define FullTransactionIdEquals(a, b)   ((a).value == (b).value)
  51 #define FullTransactionIdPrecedes(a, b) ((a).value < (b).value)
  52 #define FullTransactionIdPrecedesOrEquals(a, b) ((a).value <= (b).value)
  53 #define FullTransactionIdFollows(a, b) ((a).value > (b).value)
  54 #define FullTransactionIdFollowsOrEquals(a, b) ((a).value >= (b).value)
  55 #define FullTransactionIdIsValid(x)             TransactionIdIsValid(XidFromFullTransactionId(x))
  56 #define InvalidFullTransactionId                FullTransactionIdFromEpochAndXid(0, InvalidTransactionId)
  57 #define FirstNormalFullTransactionId    FullTransactionIdFromEpochAndXid(0, FirstNormalTransactionId)
  58 #define FullTransactionIdIsNormal(x)    FullTransactionIdFollowsOrEquals(x, FirstNormalFullTransactionId)
  59
  60 /*
  61  * A 64 bit value that contains an epoch and a TransactionId.  This is
  62  * wrapped in a struct to prevent implicit conversion to/from TransactionId.
  63  * Not all values represent valid normal XIDs.
  64  */
  65 typedef struct FullTransactionId
  66 {
  67         uint64          value;
  68 } FullTransactionId;
  69
  70 static inline FullTransactionId
  71 FullTransactionIdFromEpochAndXid(uint32 epoch, TransactionId xid)
  72 {
  73         FullTransactionId result;
  74
  75         result.value = ((uint64) epoch) << 32 | xid;
  76
  77         return result;
  78 }
  79
  80 static inline FullTransactionId
  81 FullTransactionIdFromU64(uint64 value)
  82 {
  83         FullTransactionId result;
  84
  85         result.value = value;
  86
  87         return result;
  88 }
  89
  90 /* advance a transaction ID variable, handling wraparound correctly */
  91 #define TransactionIdAdvance(dest)      \
  92         do { \
  93                 (dest)++; \
  94                 if ((dest) < FirstNormalTransactionId) \
  95                         (dest) = FirstNormalTransactionId; \
  96         } while(0)
  97
  98 /*
  99  * Retreat a FullTransactionId variable, stepping over xids that would appear
 100  * to be special only when viewed as 32bit XIDs.
 101  */
 102 static inline void
 103 FullTransactionIdRetreat(FullTransactionId *dest)
 104 {
 105         dest->value--;
 106
 107         /*
 108          * In contrast to 32bit XIDs don't step over the "actual" special xids.
 109          * For 64bit xids these can't be reached as part of a wraparound as they
 110          * can in the 32bit case.
 111          */
 112         if (FullTransactionIdPrecedes(*dest, FirstNormalFullTransactionId))
 113                 return;
 114
 115         /*
 116          * But we do need to step over XIDs that'd appear special only for 32bit
 117          * XIDs.
 118          */
 119         while (XidFromFullTransactionId(*dest) < FirstNormalTransactionId)
 120                 dest->value--;
 121 }
 122
 123 /*
 124  * Advance a FullTransactionId variable, stepping over xids that would appear
 125  * to be special only when viewed as 32bit XIDs.
 126  */
 127 static inline void
 128 FullTransactionIdAdvance(FullTransactionId *dest)
 129 {
 130         dest->value++;
 131
 132         /* see FullTransactionIdAdvance() */
 133         if (FullTransactionIdPrecedes(*dest, FirstNormalFullTransactionId))
 134                 return;
 135
 136         while (XidFromFullTransactionId(*dest) < FirstNormalTransactionId)
 137                 dest->value++;
 138 }
 139
 140 /* back up a transaction ID variable, handling wraparound correctly */
 141 #define TransactionIdRetreat(dest)      \
 142         do { \
 143                 (dest)--; \
 144         } while ((dest) < FirstNormalTransactionId)
 145
 146 /* compare two XIDs already known to be normal; this is a macro for speed */
 147 #define NormalTransactionIdPrecedes(id1, id2) \
 148         (AssertMacro(TransactionIdIsNormal(id1) && TransactionIdIsNormal(id2)), \
 149         (int32) ((id1) - (id2)) < 0)
 150
 151 /* compare two XIDs already known to be normal; this is a macro for speed */
 152 #define NormalTransactionIdFollows(id1, id2) \
 153         (AssertMacro(TransactionIdIsNormal(id1) && TransactionIdIsNormal(id2)), \
 154         (int32) ((id1) - (id2)) > 0)
 155
 156 /* ----------
 157  *              Object ID (OID) zero is InvalidOid.
 158  *
 159  *              OIDs 1-9999 are reserved for manual assignment (see .dat files in
 160  *              src/include/catalog/).  Of these, 8000-9999 are reserved for
 161  *              development purposes (such as in-progress patches and forks);
 162  *              they should not appear in released versions.
 163  *
 164  *              OIDs 10000-11999 are reserved for assignment by genbki.pl, for use
 165  *              when the .dat files in src/include/catalog/ do not specify an OID
 166  *              for a catalog entry that requires one.  Note that genbki.pl assigns
 167  *              these OIDs independently in each catalog, so they're not guaranteed
 168  *              to be globally unique.  Furthermore, the bootstrap backend and
 169  *              initdb's post-bootstrap processing can also assign OIDs in this range.
 170  *              The normal OID-generation logic takes care of any OID conflicts that
 171  *              might arise from that.
 172  *
 173  *              OIDs 12000-16383 are reserved for unpinned objects created by initdb's
 174  *              post-bootstrap processing.  initdb forces the OID generator up to
 175  *              12000 as soon as it's made the pinned objects it's responsible for.
 176  *
 177  *              OIDs beginning at 16384 are assigned from the OID generator
 178  *              during normal multiuser operation.  (We force the generator up to
 179  *              16384 as soon as we are in normal operation.)
 180  *
 181  * The choices of 8000, 10000 and 12000 are completely arbitrary, and can be
 182  * moved if we run low on OIDs in any category.  Changing the macros below,
 183  * and updating relevant documentation (see bki.sgml and RELEASE_CHANGES),
 184  * should be sufficient to do this.  Moving the 16384 boundary between
 185  * initdb-assigned OIDs and user-defined objects would be substantially
 186  * more painful, however, since some user-defined OIDs will appear in
 187  * on-disk data; such a change would probably break pg_upgrade.
 188  *
 189  * NOTE: if the OID generator wraps around, we skip over OIDs 0-16383
 190  * and resume with 16384.  This minimizes the odds of OID conflict, by not
 191  * reassigning OIDs that might have been assigned during initdb.  Critically,
 192  * it also ensures that no user-created object will be considered pinned.
 193  * ----------
 194  */
 195 #define FirstGenbkiObjectId             10000
 196 #define FirstUnpinnedObjectId   12000
 197 #define FirstNormalObjectId             16384
 198
 199 /*
 200  * TransamVariables is a data structure in shared memory that is used to track
 201  * OID and XID assignment state.  For largely historical reasons, there is
 202  * just one struct with different fields that are protected by different
 203  * LWLocks.
 204  *
 205  * Note: xidWrapLimit and oldestXidDB are not "active" values, but are
 206  * used just to generate useful messages when xidWarnLimit or xidStopLimit
 207  * are exceeded.
 208  */
 209 typedef struct TransamVariablesData
 210 {
 211         /*
 212          * These fields are protected by OidGenLock.
 213          */
 214         Oid                     nextOid;                /* next OID to assign */
 215         uint32          oidCount;               /* OIDs available before must do XLOG work */
 216
 217         /*
 218          * These fields are protected by XidGenLock.
 219          */
 220         FullTransactionId nextXid;      /* next XID to assign */
 221
 222         TransactionId oldestXid;        /* cluster-wide minimum datfrozenxid */
 223         TransactionId xidVacLimit;      /* start forcing autovacuums here */
 224         TransactionId xidWarnLimit; /* start complaining here */
 225         TransactionId xidStopLimit; /* refuse to advance nextXid beyond here */
 226         TransactionId xidWrapLimit; /* where the world ends */
 227         Oid                     oldestXidDB;    /* database with minimum datfrozenxid */
 228
 229         /*
 230          * These fields are protected by CommitTsLock
 231          */
 232         TransactionId oldestCommitTsXid;
 233         TransactionId newestCommitTsXid;
 234
 235         /*
 236          * These fields are protected by ProcArrayLock.
 237          */
 238         FullTransactionId latestCompletedXid;   /* newest full XID that has
 239                                                                                          * committed or aborted */
 240
 241         /*
 242          * Number of top-level transactions with xids (i.e. which may have
 243          * modified the database) that completed in some form since the start of
 244          * the server. This currently is solely used to check whether
 245          * GetSnapshotData() needs to recompute the contents of the snapshot, or
 246          * not. There are likely other users of this.  Always above 1.
 247          */
 248         uint64          xactCompletionCount;
 249
 250         /*
 251          * These fields are protected by XactTruncationLock
 252          */
 253         TransactionId oldestClogXid;    /* oldest it's safe to look up in clog */
 254
 255 } TransamVariablesData;
 256
 257
 258 /* ----------------
 259  *              extern declarations
 260  * ----------------
 261  */
 262
 263 /* in transam/xact.c */
 264 extern bool TransactionStartedDuringRecovery(void);
 265
 266 /* in transam/varsup.c */
 267 extern PGDLLIMPORT TransamVariablesData *TransamVariables;
 268
 269 /*
 270  * prototypes for functions in transam/transam.c
 271  */
 272 extern bool TransactionIdDidCommit(TransactionId transactionId);
 273 extern bool TransactionIdDidAbort(TransactionId transactionId);
 274 extern void TransactionIdCommitTree(TransactionId xid, int nxids, TransactionId *xids);
 275 extern void TransactionIdAsyncCommitTree(TransactionId xid, int nxids, TransactionId *xids, XLogRecPtr lsn);
 276 extern void TransactionIdAbortTree(TransactionId xid, int nxids, TransactionId *xids);
 277 extern bool TransactionIdPrecedes(TransactionId id1, TransactionId id2);
 278 extern bool TransactionIdPrecedesOrEquals(TransactionId id1, TransactionId id2);
 279 extern bool TransactionIdFollows(TransactionId id1, TransactionId id2);
 280 extern bool TransactionIdFollowsOrEquals(TransactionId id1, TransactionId id2);
 281 extern TransactionId TransactionIdLatest(TransactionId mainxid,
 282                                                                                  int nxids, const TransactionId *xids);
 283 extern XLogRecPtr TransactionIdGetCommitLSN(TransactionId xid);
 284
 285 /* in transam/varsup.c */
 286 extern Size VarsupShmemSize(void);
 287 extern void VarsupShmemInit(void);
 288 extern FullTransactionId GetNewTransactionId(bool isSubXact);
 289 extern void AdvanceNextFullTransactionIdPastXid(TransactionId xid);
 290 extern FullTransactionId ReadNextFullTransactionId(void);
 291 extern void SetTransactionIdLimit(TransactionId oldest_datfrozenxid,
 292                                                                   Oid oldest_datoid);
 293 extern void AdvanceOldestClogXid(TransactionId oldest_datfrozenxid);
 294 extern bool ForceTransactionIdLimitUpdate(void);
 295 extern Oid      GetNewObjectId(void);
 296 extern void StopGeneratingPinnedObjectIds(void);
 297
 298 #ifdef USE_ASSERT_CHECKING
 299 extern void AssertTransactionIdInAllowableRange(TransactionId xid);
 300 #else
 301 #define AssertTransactionIdInAllowableRange(xid) ((void)true)
 302 #endif
 303
 304 /*
 305  * Some frontend programs include this header.  For compilers that emit static
 306  * inline functions even when they're unused, that leads to unsatisfied
 307  * external references; hence hide them with #ifndef FRONTEND.
 308  */
 309 #ifndef FRONTEND
 310
 311 /*
 312  * For callers that just need the XID part of the next transaction ID.
 313  */
 314 static inline TransactionId
 315 ReadNextTransactionId(void)
 316 {
 317         return XidFromFullTransactionId(ReadNextFullTransactionId());
 318 }
 319
 320 /* return transaction ID backed up by amount, handling wraparound correctly */
 321 static inline TransactionId
 322 TransactionIdRetreatedBy(TransactionId xid, uint32 amount)
 323 {
 324         xid -= amount;
 325
 326         while (xid < FirstNormalTransactionId)
 327                 xid--;
 328
 329         return xid;
 330 }
 331
 332 /* return the older of the two IDs */
 333 static inline TransactionId
 334 TransactionIdOlder(TransactionId a, TransactionId b)
 335 {
 336         if (!TransactionIdIsValid(a))
 337                 return b;
 338
 339         if (!TransactionIdIsValid(b))
 340                 return a;
 341
 342         if (TransactionIdPrecedes(a, b))
 343                 return a;
 344         return b;
 345 }
 346
 347 /* return the older of the two IDs, assuming they're both normal */
 348 static inline TransactionId
 349 NormalTransactionIdOlder(TransactionId a, TransactionId b)
 350 {
 351         Assert(TransactionIdIsNormal(a));
 352         Assert(TransactionIdIsNormal(b));
 353         if (NormalTransactionIdPrecedes(a, b))
 354                 return a;
 355         return b;
 356 }
 357
 358 /* return the newer of the two IDs */
 359 static inline FullTransactionId
 360 FullTransactionIdNewer(FullTransactionId a, FullTransactionId b)
 361 {
 362         if (!FullTransactionIdIsValid(a))
 363                 return b;
 364
 365         if (!FullTransactionIdIsValid(b))
 366                 return a;
 367
 368         if (FullTransactionIdFollows(a, b))
 369                 return a;
 370         return b;
 371 }
 372
 373 #endif                                                  /* FRONTEND */
 374
 375 #endif                                                  /* TRANSAM_H */