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twophase.c
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1 /*-------------------------------------------------------------------------
2  *
3  * twophase.c
4  * Two-phase commit support functions.
5  *
6  * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
7  * Portions Copyright (c) 1994, Regents of the University of California
8  *
9  * IDENTIFICATION
10  * src/backend/access/transam/twophase.c
11  *
12  * NOTES
13  * Each global transaction is associated with a global transaction
14  * identifier (GID). The client assigns a GID to a postgres
15  * transaction with the PREPARE TRANSACTION command.
16  *
17  * We keep all active global transactions in a shared memory array.
18  * When the PREPARE TRANSACTION command is issued, the GID is
19  * reserved for the transaction in the array. This is done before
20  * a WAL entry is made, because the reservation checks for duplicate
21  * GIDs and aborts the transaction if there already is a global
22  * transaction in prepared state with the same GID.
23  *
24  * A global transaction (gxact) also has dummy PGXACT and PGPROC; this is
25  * what keeps the XID considered running by TransactionIdIsInProgress.
26  * It is also convenient as a PGPROC to hook the gxact's locks to.
27  *
28  * Information to recover prepared transactions in case of crash is
29  * now stored in WAL for the common case. In some cases there will be
30  * an extended period between preparing a GXACT and commit/abort, in
31  * which case we need to separately record prepared transaction data
32  * in permanent storage. This includes locking information, pending
33  * notifications etc. All that state information is written to the
34  * per-transaction state file in the pg_twophase directory.
35  * All prepared transactions will be written prior to shutdown.
36  *
37  * Life track of state data is following:
38  *
39  * * On PREPARE TRANSACTION backend writes state data only to the WAL and
40  * stores pointer to the start of the WAL record in
41  * gxact->prepare_start_lsn.
42  * * If COMMIT occurs before checkpoint then backend reads data from WAL
43  * using prepare_start_lsn.
44  * * On checkpoint state data copied to files in pg_twophase directory and
45  * fsynced
46  * * If COMMIT happens after checkpoint then backend reads state data from
47  * files
48  *
49  * During replay and replication, TwoPhaseState also holds information
50  * about active prepared transactions that haven't been moved to disk yet.
51  *
52  * Replay of twophase records happens by the following rules:
53  *
54  * * At the beginning of recovery, pg_twophase is scanned once, filling
55  * TwoPhaseState with entries marked with gxact->inredo and
56  * gxact->ondisk. Two-phase file data older than the XID horizon of
57  * the redo position are discarded.
58  * * On PREPARE redo, the transaction is added to TwoPhaseState->prepXacts.
59  * gxact->inredo is set to true for such entries.
60  * * On Checkpoint we iterate through TwoPhaseState->prepXacts entries
61  * that have gxact->inredo set and are behind the redo_horizon. We
62  * save them to disk and then switch gxact->ondisk to true.
63  * * On COMMIT/ABORT we delete the entry from TwoPhaseState->prepXacts.
64  * If gxact->ondisk is true, the corresponding entry from the disk
65  * is additionally deleted.
66  * * RecoverPreparedTransactions(), StandbyRecoverPreparedTransactions()
67  * and PrescanPreparedTransactions() have been modified to go through
68  * gxact->inredo entries that have not made it to disk.
69  *
70  *-------------------------------------------------------------------------
71  */
72 #include "postgres.h"
73 
74 #include <fcntl.h>
75 #include <sys/stat.h>
76 #include <time.h>
77 #include <unistd.h>
78 
79 #include "access/commit_ts.h"
80 #include "access/htup_details.h"
81 #include "access/subtrans.h"
82 #include "access/transam.h"
83 #include "access/twophase.h"
84 #include "access/twophase_rmgr.h"
85 #include "access/xact.h"
86 #include "access/xlog.h"
87 #include "access/xloginsert.h"
88 #include "access/xlogutils.h"
89 #include "access/xlogreader.h"
90 #include "catalog/pg_type.h"
91 #include "catalog/storage.h"
92 #include "funcapi.h"
93 #include "miscadmin.h"
94 #include "pg_trace.h"
95 #include "pgstat.h"
96 #include "replication/origin.h"
97 #include "replication/syncrep.h"
98 #include "replication/walsender.h"
99 #include "storage/fd.h"
100 #include "storage/ipc.h"
101 #include "storage/predicate.h"
102 #include "storage/proc.h"
103 #include "storage/procarray.h"
104 #include "storage/sinvaladt.h"
105 #include "storage/smgr.h"
106 #include "utils/builtins.h"
107 #include "utils/memutils.h"
108 #include "utils/timestamp.h"
109 
110 
111 /*
112  * Directory where Two-phase commit files reside within PGDATA
113  */
114 #define TWOPHASE_DIR "pg_twophase"
115 
116 /* GUC variable, can't be changed after startup */
118 
119 /*
120  * This struct describes one global transaction that is in prepared state
121  * or attempting to become prepared.
122  *
123  * The lifecycle of a global transaction is:
124  *
125  * 1. After checking that the requested GID is not in use, set up an entry in
126  * the TwoPhaseState->prepXacts array with the correct GID and valid = false,
127  * and mark it as locked by my backend.
128  *
129  * 2. After successfully completing prepare, set valid = true and enter the
130  * referenced PGPROC into the global ProcArray.
131  *
132  * 3. To begin COMMIT PREPARED or ROLLBACK PREPARED, check that the entry is
133  * valid and not locked, then mark the entry as locked by storing my current
134  * backend ID into locking_backend. This prevents concurrent attempts to
135  * commit or rollback the same prepared xact.
136  *
137  * 4. On completion of COMMIT PREPARED or ROLLBACK PREPARED, remove the entry
138  * from the ProcArray and the TwoPhaseState->prepXacts array and return it to
139  * the freelist.
140  *
141  * Note that if the preparing transaction fails between steps 1 and 2, the
142  * entry must be removed so that the GID and the GlobalTransaction struct
143  * can be reused. See AtAbort_Twophase().
144  *
145  * typedef struct GlobalTransactionData *GlobalTransaction appears in
146  * twophase.h
147  *
148  * Note that the max value of GIDSIZE must fit in the uint16 gidlen,
149  * specified in TwoPhaseFileHeader.
150  */
151 #define GIDSIZE 200
152 
153 typedef struct GlobalTransactionData
154 {
155  GlobalTransaction next; /* list link for free list */
156  int pgprocno; /* ID of associated dummy PGPROC */
157  BackendId dummyBackendId; /* similar to backend id for backends */
158  TimestampTz prepared_at; /* time of preparation */
159 
160  /*
161  * Note that we need to keep track of two LSNs for each GXACT. We keep
162  * track of the start LSN because this is the address we must use to read
163  * state data back from WAL when committing a prepared GXACT. We keep
164  * track of the end LSN because that is the LSN we need to wait for prior
165  * to commit.
166  */
167  XLogRecPtr prepare_start_lsn; /* XLOG offset of prepare record start */
168  XLogRecPtr prepare_end_lsn; /* XLOG offset of prepare record end */
169  TransactionId xid; /* The GXACT id */
170 
171  Oid owner; /* ID of user that executed the xact */
172  BackendId locking_backend; /* backend currently working on the xact */
173  bool valid; /* TRUE if PGPROC entry is in proc array */
174  bool ondisk; /* TRUE if prepare state file is on disk */
175  bool inredo; /* TRUE if entry was added via xlog_redo */
176  char gid[GIDSIZE]; /* The GID assigned to the prepared xact */
178 
179 /*
180  * Two Phase Commit shared state. Access to this struct is protected
181  * by TwoPhaseStateLock.
182  */
183 typedef struct TwoPhaseStateData
184 {
185  /* Head of linked list of free GlobalTransactionData structs */
187 
188  /* Number of valid prepXacts entries. */
190 
191  /* There are max_prepared_xacts items in this array */
192  GlobalTransaction prepXacts[FLEXIBLE_ARRAY_MEMBER];
194 
196 
197 /*
198  * Global transaction entry currently locked by us, if any. Note that any
199  * access to the entry pointed to by this variable must be protected by
200  * TwoPhaseStateLock, though obviously the pointer itself doesn't need to be
201  * (since it's just local memory).
202  */
204 
205 static bool twophaseExitRegistered = false;
206 
208  int nchildren,
209  TransactionId *children,
210  int nrels,
211  RelFileNode *rels,
212  int ninvalmsgs,
213  SharedInvalidationMessage *invalmsgs,
214  bool initfileinval);
216  int nchildren,
217  TransactionId *children,
218  int nrels,
219  RelFileNode *rels);
220 static void ProcessRecords(char *bufptr, TransactionId xid,
221  const TwoPhaseCallback callbacks[]);
222 static void RemoveGXact(GlobalTransaction gxact);
223 
224 static void XlogReadTwoPhaseData(XLogRecPtr lsn, char **buf, int *len);
225 static char *ProcessTwoPhaseBuffer(TransactionId xid,
226  XLogRecPtr prepare_start_lsn,
227  bool fromdisk, bool setParent, bool setNextXid);
229  const char *gid, TimestampTz prepared_at, Oid owner,
230  Oid databaseid);
231 static void RemoveTwoPhaseFile(TransactionId xid, bool giveWarning);
232 static void RecreateTwoPhaseFile(TransactionId xid, void *content, int len);
233 
234 /*
235  * Initialization of shared memory
236  */
237 Size
239 {
240  Size size;
241 
242  /* Need the fixed struct, the array of pointers, and the GTD structs */
243  size = offsetof(TwoPhaseStateData, prepXacts);
244  size = add_size(size, mul_size(max_prepared_xacts,
245  sizeof(GlobalTransaction)));
246  size = MAXALIGN(size);
247  size = add_size(size, mul_size(max_prepared_xacts,
248  sizeof(GlobalTransactionData)));
249 
250  return size;
251 }
252 
253 void
255 {
256  bool found;
257 
258  TwoPhaseState = ShmemInitStruct("Prepared Transaction Table",
260  &found);
261  if (!IsUnderPostmaster)
262  {
263  GlobalTransaction gxacts;
264  int i;
265 
266  Assert(!found);
267  TwoPhaseState->freeGXacts = NULL;
268  TwoPhaseState->numPrepXacts = 0;
269 
270  /*
271  * Initialize the linked list of free GlobalTransactionData structs
272  */
273  gxacts = (GlobalTransaction)
274  ((char *) TwoPhaseState +
275  MAXALIGN(offsetof(TwoPhaseStateData, prepXacts) +
277  for (i = 0; i < max_prepared_xacts; i++)
278  {
279  /* insert into linked list */
280  gxacts[i].next = TwoPhaseState->freeGXacts;
281  TwoPhaseState->freeGXacts = &gxacts[i];
282 
283  /* associate it with a PGPROC assigned by InitProcGlobal */
285 
286  /*
287  * Assign a unique ID for each dummy proc, so that the range of
288  * dummy backend IDs immediately follows the range of normal
289  * backend IDs. We don't dare to assign a real backend ID to dummy
290  * procs, because prepared transactions don't take part in cache
291  * invalidation like a real backend ID would imply, but having a
292  * unique ID for them is nevertheless handy. This arrangement
293  * allows you to allocate an array of size (MaxBackends +
294  * max_prepared_xacts + 1), and have a slot for every backend and
295  * prepared transaction. Currently multixact.c uses that
296  * technique.
297  */
298  gxacts[i].dummyBackendId = MaxBackends + 1 + i;
299  }
300  }
301  else
302  Assert(found);
303 }
304 
305 /*
306  * Exit hook to unlock the global transaction entry we're working on.
307  */
308 static void
310 {
311  /* same logic as abort */
313 }
314 
315 /*
316  * Abort hook to unlock the global transaction entry we're working on.
317  */
318 void
320 {
321  if (MyLockedGxact == NULL)
322  return;
323 
324  /*
325  * What to do with the locked global transaction entry? If we were in the
326  * process of preparing the transaction, but haven't written the WAL
327  * record and state file yet, the transaction must not be considered as
328  * prepared. Likewise, if we are in the process of finishing an
329  * already-prepared transaction, and fail after having already written the
330  * 2nd phase commit or rollback record to the WAL, the transaction should
331  * not be considered as prepared anymore. In those cases, just remove the
332  * entry from shared memory.
333  *
334  * Otherwise, the entry must be left in place so that the transaction can
335  * be finished later, so just unlock it.
336  *
337  * If we abort during prepare, after having written the WAL record, we
338  * might not have transferred all locks and other state to the prepared
339  * transaction yet. Likewise, if we abort during commit or rollback,
340  * after having written the WAL record, we might not have released all the
341  * resources held by the transaction yet. In those cases, the in-memory
342  * state can be wrong, but it's too late to back out.
343  */
344  LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
345  if (!MyLockedGxact->valid)
346  RemoveGXact(MyLockedGxact);
347  else
348  MyLockedGxact->locking_backend = InvalidBackendId;
349  LWLockRelease(TwoPhaseStateLock);
350 
351  MyLockedGxact = NULL;
352 }
353 
354 /*
355  * This is called after we have finished transferring state to the prepared
356  * PGXACT entry.
357  */
358 void
360 {
361  LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
362  MyLockedGxact->locking_backend = InvalidBackendId;
363  LWLockRelease(TwoPhaseStateLock);
364 
365  MyLockedGxact = NULL;
366 }
367 
368 
369 /*
370  * MarkAsPreparing
371  * Reserve the GID for the given transaction.
372  */
374 MarkAsPreparing(TransactionId xid, const char *gid,
375  TimestampTz prepared_at, Oid owner, Oid databaseid)
376 {
377  GlobalTransaction gxact;
378  int i;
379 
380  if (strlen(gid) >= GIDSIZE)
381  ereport(ERROR,
382  (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
383  errmsg("transaction identifier \"%s\" is too long",
384  gid)));
385 
386  /* fail immediately if feature is disabled */
387  if (max_prepared_xacts == 0)
388  ereport(ERROR,
389  (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
390  errmsg("prepared transactions are disabled"),
391  errhint("Set max_prepared_transactions to a nonzero value.")));
392 
393  /* on first call, register the exit hook */
395  {
397  twophaseExitRegistered = true;
398  }
399 
400  LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
401 
402  /* Check for conflicting GID */
403  for (i = 0; i < TwoPhaseState->numPrepXacts; i++)
404  {
405  gxact = TwoPhaseState->prepXacts[i];
406  if (strcmp(gxact->gid, gid) == 0)
407  {
408  ereport(ERROR,
410  errmsg("transaction identifier \"%s\" is already in use",
411  gid)));
412  }
413  }
414 
415  /* Get a free gxact from the freelist */
416  if (TwoPhaseState->freeGXacts == NULL)
417  ereport(ERROR,
418  (errcode(ERRCODE_OUT_OF_MEMORY),
419  errmsg("maximum number of prepared transactions reached"),
420  errhint("Increase max_prepared_transactions (currently %d).",
422  gxact = TwoPhaseState->freeGXacts;
423  TwoPhaseState->freeGXacts = gxact->next;
424 
425  MarkAsPreparingGuts(gxact, xid, gid, prepared_at, owner, databaseid);
426 
427  gxact->ondisk = false;
428 
429  /* And insert it into the active array */
430  Assert(TwoPhaseState->numPrepXacts < max_prepared_xacts);
431  TwoPhaseState->prepXacts[TwoPhaseState->numPrepXacts++] = gxact;
432 
433  LWLockRelease(TwoPhaseStateLock);
434 
435  return gxact;
436 }
437 
438 /*
439  * MarkAsPreparingGuts
440  *
441  * This uses a gxact struct and puts it into the active array.
442  * NOTE: this is also used when reloading a gxact after a crash; so avoid
443  * assuming that we can use very much backend context.
444  *
445  * Note: This function should be called with appropriate locks held.
446  */
447 static void
449  TimestampTz prepared_at, Oid owner, Oid databaseid)
450 {
451  PGPROC *proc;
452  PGXACT *pgxact;
453  int i;
454 
455  Assert(LWLockHeldByMeInMode(TwoPhaseStateLock, LW_EXCLUSIVE));
456 
457  Assert(gxact != NULL);
458  proc = &ProcGlobal->allProcs[gxact->pgprocno];
459  pgxact = &ProcGlobal->allPgXact[gxact->pgprocno];
460 
461  /* Initialize the PGPROC entry */
462  MemSet(proc, 0, sizeof(PGPROC));
463  proc->pgprocno = gxact->pgprocno;
464  SHMQueueElemInit(&(proc->links));
465  proc->waitStatus = STATUS_OK;
466  /* We set up the gxact's VXID as InvalidBackendId/XID */
467  proc->lxid = (LocalTransactionId) xid;
468  pgxact->xid = xid;
469  pgxact->xmin = InvalidTransactionId;
470  pgxact->delayChkpt = false;
471  pgxact->vacuumFlags = 0;
472  proc->pid = 0;
473  proc->backendId = InvalidBackendId;
474  proc->databaseId = databaseid;
475  proc->roleId = owner;
476  proc->isBackgroundWorker = false;
477  proc->lwWaiting = false;
478  proc->lwWaitMode = 0;
479  proc->waitLock = NULL;
480  proc->waitProcLock = NULL;
481  for (i = 0; i < NUM_LOCK_PARTITIONS; i++)
482  SHMQueueInit(&(proc->myProcLocks[i]));
483  /* subxid data must be filled later by GXactLoadSubxactData */
484  pgxact->overflowed = false;
485  pgxact->nxids = 0;
486 
487  gxact->prepared_at = prepared_at;
488  gxact->xid = xid;
489  gxact->owner = owner;
490  gxact->locking_backend = MyBackendId;
491  gxact->valid = false;
492  gxact->inredo = false;
493  strcpy(gxact->gid, gid);
494 
495  /*
496  * Remember that we have this GlobalTransaction entry locked for us. If we
497  * abort after this, we must release it.
498  */
499  MyLockedGxact = gxact;
500 }
501 
502 /*
503  * GXactLoadSubxactData
504  *
505  * If the transaction being persisted had any subtransactions, this must
506  * be called before MarkAsPrepared() to load information into the dummy
507  * PGPROC.
508  */
509 static void
511  TransactionId *children)
512 {
513  PGPROC *proc = &ProcGlobal->allProcs[gxact->pgprocno];
514  PGXACT *pgxact = &ProcGlobal->allPgXact[gxact->pgprocno];
515 
516  /* We need no extra lock since the GXACT isn't valid yet */
517  if (nsubxacts > PGPROC_MAX_CACHED_SUBXIDS)
518  {
519  pgxact->overflowed = true;
520  nsubxacts = PGPROC_MAX_CACHED_SUBXIDS;
521  }
522  if (nsubxacts > 0)
523  {
524  memcpy(proc->subxids.xids, children,
525  nsubxacts * sizeof(TransactionId));
526  pgxact->nxids = nsubxacts;
527  }
528 }
529 
530 /*
531  * MarkAsPrepared
532  * Mark the GXACT as fully valid, and enter it into the global ProcArray.
533  *
534  * lock_held indicates whether caller already holds TwoPhaseStateLock.
535  */
536 static void
537 MarkAsPrepared(GlobalTransaction gxact, bool lock_held)
538 {
539  /* Lock here may be overkill, but I'm not convinced of that ... */
540  if (!lock_held)
541  LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
542  Assert(!gxact->valid);
543  gxact->valid = true;
544  if (!lock_held)
545  LWLockRelease(TwoPhaseStateLock);
546 
547  /*
548  * Put it into the global ProcArray so TransactionIdIsInProgress considers
549  * the XID as still running.
550  */
552 }
553 
554 /*
555  * LockGXact
556  * Locate the prepared transaction and mark it busy for COMMIT or PREPARE.
557  */
558 static GlobalTransaction
559 LockGXact(const char *gid, Oid user)
560 {
561  int i;
562 
563  /* on first call, register the exit hook */
565  {
567  twophaseExitRegistered = true;
568  }
569 
570  LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
571 
572  for (i = 0; i < TwoPhaseState->numPrepXacts; i++)
573  {
574  GlobalTransaction gxact = TwoPhaseState->prepXacts[i];
575  PGPROC *proc = &ProcGlobal->allProcs[gxact->pgprocno];
576 
577  /* Ignore not-yet-valid GIDs */
578  if (!gxact->valid)
579  continue;
580  if (strcmp(gxact->gid, gid) != 0)
581  continue;
582 
583  /* Found it, but has someone else got it locked? */
584  if (gxact->locking_backend != InvalidBackendId)
585  ereport(ERROR,
586  (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
587  errmsg("prepared transaction with identifier \"%s\" is busy",
588  gid)));
589 
590  if (user != gxact->owner && !superuser_arg(user))
591  ereport(ERROR,
592  (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
593  errmsg("permission denied to finish prepared transaction"),
594  errhint("Must be superuser or the user that prepared the transaction.")));
595 
596  /*
597  * Note: it probably would be possible to allow committing from
598  * another database; but at the moment NOTIFY is known not to work and
599  * there may be some other issues as well. Hence disallow until
600  * someone gets motivated to make it work.
601  */
602  if (MyDatabaseId != proc->databaseId)
603  ereport(ERROR,
604  (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
605  errmsg("prepared transaction belongs to another database"),
606  errhint("Connect to the database where the transaction was prepared to finish it.")));
607 
608  /* OK for me to lock it */
609  gxact->locking_backend = MyBackendId;
610  MyLockedGxact = gxact;
611 
612  LWLockRelease(TwoPhaseStateLock);
613 
614  return gxact;
615  }
616 
617  LWLockRelease(TwoPhaseStateLock);
618 
619  ereport(ERROR,
620  (errcode(ERRCODE_UNDEFINED_OBJECT),
621  errmsg("prepared transaction with identifier \"%s\" does not exist",
622  gid)));
623 
624  /* NOTREACHED */
625  return NULL;
626 }
627 
628 /*
629  * RemoveGXact
630  * Remove the prepared transaction from the shared memory array.
631  *
632  * NB: caller should have already removed it from ProcArray
633  */
634 static void
636 {
637  int i;
638 
639  Assert(LWLockHeldByMeInMode(TwoPhaseStateLock, LW_EXCLUSIVE));
640 
641  for (i = 0; i < TwoPhaseState->numPrepXacts; i++)
642  {
643  if (gxact == TwoPhaseState->prepXacts[i])
644  {
645  /* remove from the active array */
646  TwoPhaseState->numPrepXacts--;
647  TwoPhaseState->prepXacts[i] = TwoPhaseState->prepXacts[TwoPhaseState->numPrepXacts];
648 
649  /* and put it back in the freelist */
650  gxact->next = TwoPhaseState->freeGXacts;
651  TwoPhaseState->freeGXacts = gxact;
652 
653  return;
654  }
655  }
656 
657  elog(ERROR, "failed to find %p in GlobalTransaction array", gxact);
658 }
659 
660 /*
661  * Returns an array of all prepared transactions for the user-level
662  * function pg_prepared_xact.
663  *
664  * The returned array and all its elements are copies of internal data
665  * structures, to minimize the time we need to hold the TwoPhaseStateLock.
666  *
667  * WARNING -- we return even those transactions that are not fully prepared
668  * yet. The caller should filter them out if he doesn't want them.
669  *
670  * The returned array is palloc'd.
671  */
672 static int
674 {
675  GlobalTransaction array;
676  int num;
677  int i;
678 
679  LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
680 
681  if (TwoPhaseState->numPrepXacts == 0)
682  {
683  LWLockRelease(TwoPhaseStateLock);
684 
685  *gxacts = NULL;
686  return 0;
687  }
688 
689  num = TwoPhaseState->numPrepXacts;
690  array = (GlobalTransaction) palloc(sizeof(GlobalTransactionData) * num);
691  *gxacts = array;
692  for (i = 0; i < num; i++)
693  memcpy(array + i, TwoPhaseState->prepXacts[i],
694  sizeof(GlobalTransactionData));
695 
696  LWLockRelease(TwoPhaseStateLock);
697 
698  return num;
699 }
700 
701 
702 /* Working status for pg_prepared_xact */
703 typedef struct
704 {
706  int ngxacts;
707  int currIdx;
708 } Working_State;
709 
710 /*
711  * pg_prepared_xact
712  * Produce a view with one row per prepared transaction.
713  *
714  * This function is here so we don't have to export the
715  * GlobalTransactionData struct definition.
716  */
717 Datum
719 {
720  FuncCallContext *funcctx;
722 
723  if (SRF_IS_FIRSTCALL())
724  {
725  TupleDesc tupdesc;
726  MemoryContext oldcontext;
727 
728  /* create a function context for cross-call persistence */
729  funcctx = SRF_FIRSTCALL_INIT();
730 
731  /*
732  * Switch to memory context appropriate for multiple function calls
733  */
734  oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);
735 
736  /* build tupdesc for result tuples */
737  /* this had better match pg_prepared_xacts view in system_views.sql */
738  tupdesc = CreateTemplateTupleDesc(5, false);
739  TupleDescInitEntry(tupdesc, (AttrNumber) 1, "transaction",
740  XIDOID, -1, 0);
741  TupleDescInitEntry(tupdesc, (AttrNumber) 2, "gid",
742  TEXTOID, -1, 0);
743  TupleDescInitEntry(tupdesc, (AttrNumber) 3, "prepared",
744  TIMESTAMPTZOID, -1, 0);
745  TupleDescInitEntry(tupdesc, (AttrNumber) 4, "ownerid",
746  OIDOID, -1, 0);
747  TupleDescInitEntry(tupdesc, (AttrNumber) 5, "dbid",
748  OIDOID, -1, 0);
749 
750  funcctx->tuple_desc = BlessTupleDesc(tupdesc);
751 
752  /*
753  * Collect all the 2PC status information that we will format and send
754  * out as a result set.
755  */
756  status = (Working_State *) palloc(sizeof(Working_State));
757  funcctx->user_fctx = (void *) status;
758 
759  status->ngxacts = GetPreparedTransactionList(&status->array);
760  status->currIdx = 0;
761 
762  MemoryContextSwitchTo(oldcontext);
763  }
764 
765  funcctx = SRF_PERCALL_SETUP();
766  status = (Working_State *) funcctx->user_fctx;
767 
768  while (status->array != NULL && status->currIdx < status->ngxacts)
769  {
770  GlobalTransaction gxact = &status->array[status->currIdx++];
771  PGPROC *proc = &ProcGlobal->allProcs[gxact->pgprocno];
772  PGXACT *pgxact = &ProcGlobal->allPgXact[gxact->pgprocno];
773  Datum values[5];
774  bool nulls[5];
775  HeapTuple tuple;
776  Datum result;
777 
778  if (!gxact->valid)
779  continue;
780 
781  /*
782  * Form tuple with appropriate data.
783  */
784  MemSet(values, 0, sizeof(values));
785  MemSet(nulls, 0, sizeof(nulls));
786 
787  values[0] = TransactionIdGetDatum(pgxact->xid);
788  values[1] = CStringGetTextDatum(gxact->gid);
789  values[2] = TimestampTzGetDatum(gxact->prepared_at);
790  values[3] = ObjectIdGetDatum(gxact->owner);
791  values[4] = ObjectIdGetDatum(proc->databaseId);
792 
793  tuple = heap_form_tuple(funcctx->tuple_desc, values, nulls);
794  result = HeapTupleGetDatum(tuple);
795  SRF_RETURN_NEXT(funcctx, result);
796  }
797 
798  SRF_RETURN_DONE(funcctx);
799 }
800 
801 /*
802  * TwoPhaseGetGXact
803  * Get the GlobalTransaction struct for a prepared transaction
804  * specified by XID
805  */
806 static GlobalTransaction
808 {
810  int i;
811 
812  static TransactionId cached_xid = InvalidTransactionId;
813  static GlobalTransaction cached_gxact = NULL;
814 
815  /*
816  * During a recovery, COMMIT PREPARED, or ABORT PREPARED, we'll be called
817  * repeatedly for the same XID. We can save work with a simple cache.
818  */
819  if (xid == cached_xid)
820  return cached_gxact;
821 
822  LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
823 
824  for (i = 0; i < TwoPhaseState->numPrepXacts; i++)
825  {
826  GlobalTransaction gxact = TwoPhaseState->prepXacts[i];
827  PGXACT *pgxact = &ProcGlobal->allPgXact[gxact->pgprocno];
828 
829  if (pgxact->xid == xid)
830  {
831  result = gxact;
832  break;
833  }
834  }
835 
836  LWLockRelease(TwoPhaseStateLock);
837 
838  if (result == NULL) /* should not happen */
839  elog(ERROR, "failed to find GlobalTransaction for xid %u", xid);
840 
841  cached_xid = xid;
842  cached_gxact = result;
843 
844  return result;
845 }
846 
847 /*
848  * TwoPhaseGetDummyProc
849  * Get the dummy backend ID for prepared transaction specified by XID
850  *
851  * Dummy backend IDs are similar to real backend IDs of real backends.
852  * They start at MaxBackends + 1, and are unique across all currently active
853  * real backends and prepared transactions.
854  */
855 BackendId
857 {
858  GlobalTransaction gxact = TwoPhaseGetGXact(xid);
859 
860  return gxact->dummyBackendId;
861 }
862 
863 /*
864  * TwoPhaseGetDummyProc
865  * Get the PGPROC that represents a prepared transaction specified by XID
866  */
867 PGPROC *
869 {
870  GlobalTransaction gxact = TwoPhaseGetGXact(xid);
871 
872  return &ProcGlobal->allProcs[gxact->pgprocno];
873 }
874 
875 /************************************************************************/
876 /* State file support */
877 /************************************************************************/
878 
879 #define TwoPhaseFilePath(path, xid) \
880  snprintf(path, MAXPGPATH, TWOPHASE_DIR "/%08X", xid)
881 
882 /*
883  * 2PC state file format:
884  *
885  * 1. TwoPhaseFileHeader
886  * 2. TransactionId[] (subtransactions)
887  * 3. RelFileNode[] (files to be deleted at commit)
888  * 4. RelFileNode[] (files to be deleted at abort)
889  * 5. SharedInvalidationMessage[] (inval messages to be sent at commit)
890  * 6. TwoPhaseRecordOnDisk
891  * 7. ...
892  * 8. TwoPhaseRecordOnDisk (end sentinel, rmid == TWOPHASE_RM_END_ID)
893  * 9. checksum (CRC-32C)
894  *
895  * Each segment except the final checksum is MAXALIGN'd.
896  */
897 
898 /*
899  * Header for a 2PC state file
900  */
901 #define TWOPHASE_MAGIC 0x57F94533 /* format identifier */
902 
903 typedef struct TwoPhaseFileHeader
904 {
905  uint32 magic; /* format identifier */
906  uint32 total_len; /* actual file length */
907  TransactionId xid; /* original transaction XID */
908  Oid database; /* OID of database it was in */
909  TimestampTz prepared_at; /* time of preparation */
910  Oid owner; /* user running the transaction */
911  int32 nsubxacts; /* number of following subxact XIDs */
912  int32 ncommitrels; /* number of delete-on-commit rels */
913  int32 nabortrels; /* number of delete-on-abort rels */
914  int32 ninvalmsgs; /* number of cache invalidation messages */
915  bool initfileinval; /* does relcache init file need invalidation? */
916  uint16 gidlen; /* length of the GID - GID follows the header */
918 
919 /*
920  * Header for each record in a state file
921  *
922  * NOTE: len counts only the rmgr data, not the TwoPhaseRecordOnDisk header.
923  * The rmgr data will be stored starting on a MAXALIGN boundary.
924  */
925 typedef struct TwoPhaseRecordOnDisk
926 {
927  uint32 len; /* length of rmgr data */
928  TwoPhaseRmgrId rmid; /* resource manager for this record */
929  uint16 info; /* flag bits for use by rmgr */
931 
932 /*
933  * During prepare, the state file is assembled in memory before writing it
934  * to WAL and the actual state file. We use a chain of StateFileChunk blocks
935  * for that.
936  */
937 typedef struct StateFileChunk
938 {
939  char *data;
943 
944 static struct xllist
945 {
946  StateFileChunk *head; /* first data block in the chain */
947  StateFileChunk *tail; /* last block in chain */
949  uint32 bytes_free; /* free bytes left in tail block */
950  uint32 total_len; /* total data bytes in chain */
951 } records;
952 
953 
954 /*
955  * Append a block of data to records data structure.
956  *
957  * NB: each block is padded to a MAXALIGN multiple. This must be
958  * accounted for when the file is later read!
959  *
960  * The data is copied, so the caller is free to modify it afterwards.
961  */
962 static void
963 save_state_data(const void *data, uint32 len)
964 {
965  uint32 padlen = MAXALIGN(len);
966 
967  if (padlen > records.bytes_free)
968  {
969  records.tail->next = palloc0(sizeof(StateFileChunk));
971  records.tail->len = 0;
972  records.tail->next = NULL;
974 
975  records.bytes_free = Max(padlen, 512);
977  }
978 
979  memcpy(((char *) records.tail->data) + records.tail->len, data, len);
980  records.tail->len += padlen;
981  records.bytes_free -= padlen;
982  records.total_len += padlen;
983 }
984 
985 /*
986  * Start preparing a state file.
987  *
988  * Initializes data structure and inserts the 2PC file header record.
989  */
990 void
992 {
993  PGPROC *proc = &ProcGlobal->allProcs[gxact->pgprocno];
994  PGXACT *pgxact = &ProcGlobal->allPgXact[gxact->pgprocno];
995  TransactionId xid = pgxact->xid;
996  TwoPhaseFileHeader hdr;
997  TransactionId *children;
998  RelFileNode *commitrels;
999  RelFileNode *abortrels;
1000  SharedInvalidationMessage *invalmsgs;
1001 
1002  /* Initialize linked list */
1003  records.head = palloc0(sizeof(StateFileChunk));
1004  records.head->len = 0;
1005  records.head->next = NULL;
1006 
1007  records.bytes_free = Max(sizeof(TwoPhaseFileHeader), 512);
1009 
1011  records.num_chunks = 1;
1012 
1013  records.total_len = 0;
1014 
1015  /* Create header */
1016  hdr.magic = TWOPHASE_MAGIC;
1017  hdr.total_len = 0; /* EndPrepare will fill this in */
1018  hdr.xid = xid;
1019  hdr.database = proc->databaseId;
1020  hdr.prepared_at = gxact->prepared_at;
1021  hdr.owner = gxact->owner;
1022  hdr.nsubxacts = xactGetCommittedChildren(&children);
1023  hdr.ncommitrels = smgrGetPendingDeletes(true, &commitrels);
1024  hdr.nabortrels = smgrGetPendingDeletes(false, &abortrels);
1026  &hdr.initfileinval);
1027  hdr.gidlen = strlen(gxact->gid) + 1; /* Include '\0' */
1028 
1029  save_state_data(&hdr, sizeof(TwoPhaseFileHeader));
1030  save_state_data(gxact->gid, hdr.gidlen);
1031 
1032  /*
1033  * Add the additional info about subxacts, deletable files and cache
1034  * invalidation messages.
1035  */
1036  if (hdr.nsubxacts > 0)
1037  {
1038  save_state_data(children, hdr.nsubxacts * sizeof(TransactionId));
1039  /* While we have the child-xact data, stuff it in the gxact too */
1040  GXactLoadSubxactData(gxact, hdr.nsubxacts, children);
1041  }
1042  if (hdr.ncommitrels > 0)
1043  {
1044  save_state_data(commitrels, hdr.ncommitrels * sizeof(RelFileNode));
1045  pfree(commitrels);
1046  }
1047  if (hdr.nabortrels > 0)
1048  {
1049  save_state_data(abortrels, hdr.nabortrels * sizeof(RelFileNode));
1050  pfree(abortrels);
1051  }
1052  if (hdr.ninvalmsgs > 0)
1053  {
1054  save_state_data(invalmsgs,
1055  hdr.ninvalmsgs * sizeof(SharedInvalidationMessage));
1056  pfree(invalmsgs);
1057  }
1058 }
1059 
1060 /*
1061  * Finish preparing state data and writing it to WAL.
1062  */
1063 void
1065 {
1066  TwoPhaseFileHeader *hdr;
1067  StateFileChunk *record;
1068 
1069  /* Add the end sentinel to the list of 2PC records */
1071  NULL, 0);
1072 
1073  /* Go back and fill in total_len in the file header record */
1074  hdr = (TwoPhaseFileHeader *) records.head->data;
1075  Assert(hdr->magic == TWOPHASE_MAGIC);
1076  hdr->total_len = records.total_len + sizeof(pg_crc32c);
1077 
1078  /*
1079  * If the data size exceeds MaxAllocSize, we won't be able to read it in
1080  * ReadTwoPhaseFile. Check for that now, rather than fail in the case
1081  * where we write data to file and then re-read at commit time.
1082  */
1083  if (hdr->total_len > MaxAllocSize)
1084  ereport(ERROR,
1085  (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
1086  errmsg("two-phase state file maximum length exceeded")));
1087 
1088  /*
1089  * Now writing 2PC state data to WAL. We let the WAL's CRC protection
1090  * cover us, so no need to calculate a separate CRC.
1091  *
1092  * We have to set delayChkpt here, too; otherwise a checkpoint starting
1093  * immediately after the WAL record is inserted could complete without
1094  * fsync'ing our state file. (This is essentially the same kind of race
1095  * condition as the COMMIT-to-clog-write case that RecordTransactionCommit
1096  * uses delayChkpt for; see notes there.)
1097  *
1098  * We save the PREPARE record's location in the gxact for later use by
1099  * CheckPointTwoPhase.
1100  */
1102 
1104 
1105  MyPgXact->delayChkpt = true;
1106 
1107  XLogBeginInsert();
1108  for (record = records.head; record != NULL; record = record->next)
1109  XLogRegisterData(record->data, record->len);
1110  gxact->prepare_end_lsn = XLogInsert(RM_XACT_ID, XLOG_XACT_PREPARE);
1111  XLogFlush(gxact->prepare_end_lsn);
1112 
1113  /* If we crash now, we have prepared: WAL replay will fix things */
1114 
1115  /* Store record's start location to read that later on Commit */
1117 
1118  /*
1119  * Mark the prepared transaction as valid. As soon as xact.c marks
1120  * MyPgXact as not running our XID (which it will do immediately after
1121  * this function returns), others can commit/rollback the xact.
1122  *
1123  * NB: a side effect of this is to make a dummy ProcArray entry for the
1124  * prepared XID. This must happen before we clear the XID from MyPgXact,
1125  * else there is a window where the XID is not running according to
1126  * TransactionIdIsInProgress, and onlookers would be entitled to assume
1127  * the xact crashed. Instead we have a window where the same XID appears
1128  * twice in ProcArray, which is OK.
1129  */
1130  MarkAsPrepared(gxact, false);
1131 
1132  /*
1133  * Now we can mark ourselves as out of the commit critical section: a
1134  * checkpoint starting after this will certainly see the gxact as a
1135  * candidate for fsyncing.
1136  */
1137  MyPgXact->delayChkpt = false;
1138 
1139  /*
1140  * Remember that we have this GlobalTransaction entry locked for us. If
1141  * we crash after this point, it's too late to abort, but we must unlock
1142  * it so that the prepared transaction can be committed or rolled back.
1143  */
1144  MyLockedGxact = gxact;
1145 
1146  END_CRIT_SECTION();
1147 
1148  /*
1149  * Wait for synchronous replication, if required.
1150  *
1151  * Note that at this stage we have marked the prepare, but still show as
1152  * running in the procarray (twice!) and continue to hold locks.
1153  */
1154  SyncRepWaitForLSN(gxact->prepare_end_lsn, false);
1155 
1157  records.num_chunks = 0;
1158 }
1159 
1160 /*
1161  * Register a 2PC record to be written to state file.
1162  */
1163 void
1165  const void *data, uint32 len)
1166 {
1167  TwoPhaseRecordOnDisk record;
1168 
1169  record.rmid = rmid;
1170  record.info = info;
1171  record.len = len;
1172  save_state_data(&record, sizeof(TwoPhaseRecordOnDisk));
1173  if (len > 0)
1174  save_state_data(data, len);
1175 }
1176 
1177 
1178 /*
1179  * Read and validate the state file for xid.
1180  *
1181  * If it looks OK (has a valid magic number and CRC), return the palloc'd
1182  * contents of the file. Otherwise return NULL.
1183  */
1184 static char *
1185 ReadTwoPhaseFile(TransactionId xid, bool give_warnings)
1186 {
1187  char path[MAXPGPATH];
1188  char *buf;
1189  TwoPhaseFileHeader *hdr;
1190  int fd;
1191  struct stat stat;
1192  uint32 crc_offset;
1193  pg_crc32c calc_crc,
1194  file_crc;
1195 
1196  TwoPhaseFilePath(path, xid);
1197 
1198  fd = OpenTransientFile(path, O_RDONLY | PG_BINARY, 0);
1199  if (fd < 0)
1200  {
1201  if (give_warnings)
1202  ereport(WARNING,
1204  errmsg("could not open two-phase state file \"%s\": %m",
1205  path)));
1206  return NULL;
1207  }
1208 
1209  /*
1210  * Check file length. We can determine a lower bound pretty easily. We
1211  * set an upper bound to avoid palloc() failure on a corrupt file, though
1212  * we can't guarantee that we won't get an out of memory error anyway,
1213  * even on a valid file.
1214  */
1215  if (fstat(fd, &stat))
1216  {
1217  CloseTransientFile(fd);
1218  if (give_warnings)
1219  ereport(WARNING,
1221  errmsg("could not stat two-phase state file \"%s\": %m",
1222  path)));
1223  return NULL;
1224  }
1225 
1226  if (stat.st_size < (MAXALIGN(sizeof(TwoPhaseFileHeader)) +
1227  MAXALIGN(sizeof(TwoPhaseRecordOnDisk)) +
1228  sizeof(pg_crc32c)) ||
1229  stat.st_size > MaxAllocSize)
1230  {
1231  CloseTransientFile(fd);
1232  return NULL;
1233  }
1234 
1235  crc_offset = stat.st_size - sizeof(pg_crc32c);
1236  if (crc_offset != MAXALIGN(crc_offset))
1237  {
1238  CloseTransientFile(fd);
1239  return NULL;
1240  }
1241 
1242  /*
1243  * OK, slurp in the file.
1244  */
1245  buf = (char *) palloc(stat.st_size);
1246 
1248  if (read(fd, buf, stat.st_size) != stat.st_size)
1249  {
1251  CloseTransientFile(fd);
1252  if (give_warnings)
1253  ereport(WARNING,
1255  errmsg("could not read two-phase state file \"%s\": %m",
1256  path)));
1257  pfree(buf);
1258  return NULL;
1259  }
1260 
1262  CloseTransientFile(fd);
1263 
1264  hdr = (TwoPhaseFileHeader *) buf;
1265  if (hdr->magic != TWOPHASE_MAGIC || hdr->total_len != stat.st_size)
1266  {
1267  pfree(buf);
1268  return NULL;
1269  }
1270 
1271  INIT_CRC32C(calc_crc);
1272  COMP_CRC32C(calc_crc, buf, crc_offset);
1273  FIN_CRC32C(calc_crc);
1274 
1275  file_crc = *((pg_crc32c *) (buf + crc_offset));
1276 
1277  if (!EQ_CRC32C(calc_crc, file_crc))
1278  {
1279  pfree(buf);
1280  return NULL;
1281  }
1282 
1283  return buf;
1284 }
1285 
1286 
1287 /*
1288  * Reads 2PC data from xlog. During checkpoint this data will be moved to
1289  * twophase files and ReadTwoPhaseFile should be used instead.
1290  *
1291  * Note clearly that this function can access WAL during normal operation,
1292  * similarly to the way WALSender or Logical Decoding would do.
1293  *
1294  */
1295 static void
1296 XlogReadTwoPhaseData(XLogRecPtr lsn, char **buf, int *len)
1297 {
1298  XLogRecord *record;
1299  XLogReaderState *xlogreader;
1300  char *errormsg;
1301 
1303  if (!xlogreader)
1304  ereport(ERROR,
1305  (errcode(ERRCODE_OUT_OF_MEMORY),
1306  errmsg("out of memory"),
1307  errdetail("Failed while allocating a WAL reading processor.")));
1308 
1309  record = XLogReadRecord(xlogreader, lsn, &errormsg);
1310  if (record == NULL)
1311  ereport(ERROR,
1313  errmsg("could not read two-phase state from WAL at %X/%X",
1314  (uint32) (lsn >> 32),
1315  (uint32) lsn)));
1316 
1317  if (XLogRecGetRmid(xlogreader) != RM_XACT_ID ||
1319  ereport(ERROR,
1321  errmsg("expected two-phase state data is not present in WAL at %X/%X",
1322  (uint32) (lsn >> 32),
1323  (uint32) lsn)));
1324 
1325  if (len != NULL)
1326  *len = XLogRecGetDataLen(xlogreader);
1327 
1328  *buf = palloc(sizeof(char) * XLogRecGetDataLen(xlogreader));
1329  memcpy(*buf, XLogRecGetData(xlogreader), sizeof(char) * XLogRecGetDataLen(xlogreader));
1330 
1331  XLogReaderFree(xlogreader);
1332 }
1333 
1334 
1335 /*
1336  * Confirms an xid is prepared, during recovery
1337  */
1338 bool
1340 {
1341  char *buf;
1342  TwoPhaseFileHeader *hdr;
1343  bool result;
1344 
1346 
1347  if (max_prepared_xacts <= 0)
1348  return false; /* nothing to do */
1349 
1350  /* Read and validate file */
1351  buf = ReadTwoPhaseFile(xid, false);
1352  if (buf == NULL)
1353  return false;
1354 
1355  /* Check header also */
1356  hdr = (TwoPhaseFileHeader *) buf;
1357  result = TransactionIdEquals(hdr->xid, xid);
1358  pfree(buf);
1359 
1360  return result;
1361 }
1362 
1363 /*
1364  * FinishPreparedTransaction: execute COMMIT PREPARED or ROLLBACK PREPARED
1365  */
1366 void
1367 FinishPreparedTransaction(const char *gid, bool isCommit)
1368 {
1369  GlobalTransaction gxact;
1370  PGPROC *proc;
1371  PGXACT *pgxact;
1372  TransactionId xid;
1373  char *buf;
1374  char *bufptr;
1375  TwoPhaseFileHeader *hdr;
1376  TransactionId latestXid;
1377  TransactionId *children;
1378  RelFileNode *commitrels;
1379  RelFileNode *abortrels;
1380  RelFileNode *delrels;
1381  int ndelrels;
1382  SharedInvalidationMessage *invalmsgs;
1383  int i;
1384 
1385  /*
1386  * Validate the GID, and lock the GXACT to ensure that two backends do not
1387  * try to commit the same GID at once.
1388  */
1389  gxact = LockGXact(gid, GetUserId());
1390  proc = &ProcGlobal->allProcs[gxact->pgprocno];
1391  pgxact = &ProcGlobal->allPgXact[gxact->pgprocno];
1392  xid = pgxact->xid;
1393 
1394  /*
1395  * Read and validate 2PC state data. State data will typically be stored
1396  * in WAL files if the LSN is after the last checkpoint record, or moved
1397  * to disk if for some reason they have lived for a long time.
1398  */
1399  if (gxact->ondisk)
1400  buf = ReadTwoPhaseFile(xid, true);
1401  else
1403 
1404 
1405  /*
1406  * Disassemble the header area
1407  */
1408  hdr = (TwoPhaseFileHeader *) buf;
1409  Assert(TransactionIdEquals(hdr->xid, xid));
1410  bufptr = buf + MAXALIGN(sizeof(TwoPhaseFileHeader));
1411  bufptr += MAXALIGN(hdr->gidlen);
1412  children = (TransactionId *) bufptr;
1413  bufptr += MAXALIGN(hdr->nsubxacts * sizeof(TransactionId));
1414  commitrels = (RelFileNode *) bufptr;
1415  bufptr += MAXALIGN(hdr->ncommitrels * sizeof(RelFileNode));
1416  abortrels = (RelFileNode *) bufptr;
1417  bufptr += MAXALIGN(hdr->nabortrels * sizeof(RelFileNode));
1418  invalmsgs = (SharedInvalidationMessage *) bufptr;
1419  bufptr += MAXALIGN(hdr->ninvalmsgs * sizeof(SharedInvalidationMessage));
1420 
1421  /* compute latestXid among all children */
1422  latestXid = TransactionIdLatest(xid, hdr->nsubxacts, children);
1423 
1424  /*
1425  * The order of operations here is critical: make the XLOG entry for
1426  * commit or abort, then mark the transaction committed or aborted in
1427  * pg_xact, then remove its PGPROC from the global ProcArray (which means
1428  * TransactionIdIsInProgress will stop saying the prepared xact is in
1429  * progress), then run the post-commit or post-abort callbacks. The
1430  * callbacks will release the locks the transaction held.
1431  */
1432  if (isCommit)
1434  hdr->nsubxacts, children,
1435  hdr->ncommitrels, commitrels,
1436  hdr->ninvalmsgs, invalmsgs,
1437  hdr->initfileinval);
1438  else
1440  hdr->nsubxacts, children,
1441  hdr->nabortrels, abortrels);
1442 
1443  ProcArrayRemove(proc, latestXid);
1444 
1445  /*
1446  * In case we fail while running the callbacks, mark the gxact invalid so
1447  * no one else will try to commit/rollback, and so it will be recycled if
1448  * we fail after this point. It is still locked by our backend so it
1449  * won't go away yet.
1450  *
1451  * (We assume it's safe to do this without taking TwoPhaseStateLock.)
1452  */
1453  gxact->valid = false;
1454 
1455  /*
1456  * We have to remove any files that were supposed to be dropped. For
1457  * consistency with the regular xact.c code paths, must do this before
1458  * releasing locks, so do it before running the callbacks.
1459  *
1460  * NB: this code knows that we couldn't be dropping any temp rels ...
1461  */
1462  if (isCommit)
1463  {
1464  delrels = commitrels;
1465  ndelrels = hdr->ncommitrels;
1466  }
1467  else
1468  {
1469  delrels = abortrels;
1470  ndelrels = hdr->nabortrels;
1471  }
1472  for (i = 0; i < ndelrels; i++)
1473  {
1474  SMgrRelation srel = smgropen(delrels[i], InvalidBackendId);
1475 
1476  smgrdounlink(srel, false);
1477  smgrclose(srel);
1478  }
1479 
1480  /*
1481  * Handle cache invalidation messages.
1482  *
1483  * Relcache init file invalidation requires processing both before and
1484  * after we send the SI messages. See AtEOXact_Inval()
1485  */
1486  if (hdr->initfileinval)
1488  SendSharedInvalidMessages(invalmsgs, hdr->ninvalmsgs);
1489  if (hdr->initfileinval)
1491 
1492  /* And now do the callbacks */
1493  if (isCommit)
1495  else
1497 
1498  PredicateLockTwoPhaseFinish(xid, isCommit);
1499 
1500  /* Count the prepared xact as committed or aborted */
1501  AtEOXact_PgStat(isCommit);
1502 
1503  /*
1504  * And now we can clean up any files we may have left.
1505  */
1506  if (gxact->ondisk)
1507  RemoveTwoPhaseFile(xid, true);
1508 
1509  LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
1510  RemoveGXact(gxact);
1511  LWLockRelease(TwoPhaseStateLock);
1512  MyLockedGxact = NULL;
1513 
1514  pfree(buf);
1515 }
1516 
1517 /*
1518  * Scan 2PC state data in memory and call the indicated callbacks for each 2PC record.
1519  */
1520 static void
1521 ProcessRecords(char *bufptr, TransactionId xid,
1522  const TwoPhaseCallback callbacks[])
1523 {
1524  for (;;)
1525  {
1526  TwoPhaseRecordOnDisk *record = (TwoPhaseRecordOnDisk *) bufptr;
1527 
1528  Assert(record->rmid <= TWOPHASE_RM_MAX_ID);
1529  if (record->rmid == TWOPHASE_RM_END_ID)
1530  break;
1531 
1532  bufptr += MAXALIGN(sizeof(TwoPhaseRecordOnDisk));
1533 
1534  if (callbacks[record->rmid] != NULL)
1535  callbacks[record->rmid] (xid, record->info,
1536  (void *) bufptr, record->len);
1537 
1538  bufptr += MAXALIGN(record->len);
1539  }
1540 }
1541 
1542 /*
1543  * Remove the 2PC file for the specified XID.
1544  *
1545  * If giveWarning is false, do not complain about file-not-present;
1546  * this is an expected case during WAL replay.
1547  */
1548 static void
1549 RemoveTwoPhaseFile(TransactionId xid, bool giveWarning)
1550 {
1551  char path[MAXPGPATH];
1552 
1553  TwoPhaseFilePath(path, xid);
1554  if (unlink(path))
1555  if (errno != ENOENT || giveWarning)
1556  ereport(WARNING,
1558  errmsg("could not remove two-phase state file \"%s\": %m",
1559  path)));
1560 }
1561 
1562 /*
1563  * Recreates a state file. This is used in WAL replay and during
1564  * checkpoint creation.
1565  *
1566  * Note: content and len don't include CRC.
1567  */
1568 static void
1569 RecreateTwoPhaseFile(TransactionId xid, void *content, int len)
1570 {
1571  char path[MAXPGPATH];
1572  pg_crc32c statefile_crc;
1573  int fd;
1574 
1575  /* Recompute CRC */
1576  INIT_CRC32C(statefile_crc);
1577  COMP_CRC32C(statefile_crc, content, len);
1578  FIN_CRC32C(statefile_crc);
1579 
1580  TwoPhaseFilePath(path, xid);
1581 
1582  fd = OpenTransientFile(path,
1583  O_CREAT | O_TRUNC | O_WRONLY | PG_BINARY,
1584  S_IRUSR | S_IWUSR);
1585  if (fd < 0)
1586  ereport(ERROR,
1588  errmsg("could not recreate two-phase state file \"%s\": %m",
1589  path)));
1590 
1591  /* Write content and CRC */
1593  if (write(fd, content, len) != len)
1594  {
1596  CloseTransientFile(fd);
1597  ereport(ERROR,
1599  errmsg("could not write two-phase state file: %m")));
1600  }
1601  if (write(fd, &statefile_crc, sizeof(pg_crc32c)) != sizeof(pg_crc32c))
1602  {
1604  CloseTransientFile(fd);
1605  ereport(ERROR,
1607  errmsg("could not write two-phase state file: %m")));
1608  }
1610 
1611  /*
1612  * We must fsync the file because the end-of-replay checkpoint will not do
1613  * so, there being no GXACT in shared memory yet to tell it to.
1614  */
1616  if (pg_fsync(fd) != 0)
1617  {
1618  CloseTransientFile(fd);
1619  ereport(ERROR,
1621  errmsg("could not fsync two-phase state file: %m")));
1622  }
1624 
1625  if (CloseTransientFile(fd) != 0)
1626  ereport(ERROR,
1628  errmsg("could not close two-phase state file: %m")));
1629 }
1630 
1631 /*
1632  * CheckPointTwoPhase -- handle 2PC component of checkpointing.
1633  *
1634  * We must fsync the state file of any GXACT that is valid or has been
1635  * generated during redo and has a PREPARE LSN <= the checkpoint's redo
1636  * horizon. (If the gxact isn't valid yet, has not been generated in
1637  * redo, or has a later LSN, this checkpoint is not responsible for
1638  * fsyncing it.)
1639  *
1640  * This is deliberately run as late as possible in the checkpoint sequence,
1641  * because GXACTs ordinarily have short lifespans, and so it is quite
1642  * possible that GXACTs that were valid at checkpoint start will no longer
1643  * exist if we wait a little bit. With typical checkpoint settings this
1644  * will be about 3 minutes for an online checkpoint, so as a result we
1645  * we expect that there will be no GXACTs that need to be copied to disk.
1646  *
1647  * If a GXACT remains valid across multiple checkpoints, it will already
1648  * be on disk so we don't bother to repeat that write.
1649  */
1650 void
1652 {
1653  int i;
1654  int serialized_xacts = 0;
1655 
1656  if (max_prepared_xacts <= 0)
1657  return; /* nothing to do */
1658 
1659  TRACE_POSTGRESQL_TWOPHASE_CHECKPOINT_START();
1660 
1661  /*
1662  * We are expecting there to be zero GXACTs that need to be copied to
1663  * disk, so we perform all I/O while holding TwoPhaseStateLock for
1664  * simplicity. This prevents any new xacts from preparing while this
1665  * occurs, which shouldn't be a problem since the presence of long-lived
1666  * prepared xacts indicates the transaction manager isn't active.
1667  *
1668  * It's also possible to move I/O out of the lock, but on every error we
1669  * should check whether somebody committed our transaction in different
1670  * backend. Let's leave this optimization for future, if somebody will
1671  * spot that this place cause bottleneck.
1672  *
1673  * Note that it isn't possible for there to be a GXACT with a
1674  * prepare_end_lsn set prior to the last checkpoint yet is marked invalid,
1675  * because of the efforts with delayChkpt.
1676  */
1677  LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
1678  for (i = 0; i < TwoPhaseState->numPrepXacts; i++)
1679  {
1680  /*
1681  * Note that we are using gxact not pgxact so this works in recovery
1682  * also
1683  */
1684  GlobalTransaction gxact = TwoPhaseState->prepXacts[i];
1685 
1686  if ((gxact->valid || gxact->inredo) &&
1687  !gxact->ondisk &&
1688  gxact->prepare_end_lsn <= redo_horizon)
1689  {
1690  char *buf;
1691  int len;
1692 
1693  XlogReadTwoPhaseData(gxact->prepare_start_lsn, &buf, &len);
1694  RecreateTwoPhaseFile(gxact->xid, buf, len);
1695  gxact->ondisk = true;
1698  pfree(buf);
1699  serialized_xacts++;
1700  }
1701  }
1702  LWLockRelease(TwoPhaseStateLock);
1703 
1704  /*
1705  * Flush unconditionally the parent directory to make any information
1706  * durable on disk. Two-phase files could have been removed and those
1707  * removals need to be made persistent as well as any files newly created
1708  * previously since the last checkpoint.
1709  */
1710  fsync_fname(TWOPHASE_DIR, true);
1711 
1712  TRACE_POSTGRESQL_TWOPHASE_CHECKPOINT_DONE();
1713 
1714  if (log_checkpoints && serialized_xacts > 0)
1715  ereport(LOG,
1716  (errmsg_plural("%u two-phase state file was written "
1717  "for a long-running prepared transaction",
1718  "%u two-phase state files were written "
1719  "for long-running prepared transactions",
1720  serialized_xacts,
1721  serialized_xacts)));
1722 }
1723 
1724 /*
1725  * restoreTwoPhaseData
1726  *
1727  * Scan pg_twophase and fill TwoPhaseState depending on the on-disk data.
1728  * This is called once at the beginning of recovery, saving any extra
1729  * lookups in the future. Two-phase files that are newer than the
1730  * minimum XID horizon are discarded on the way.
1731  */
1732 void
1734 {
1735  DIR *cldir;
1736  struct dirent *clde;
1737 
1738  cldir = AllocateDir(TWOPHASE_DIR);
1739  LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
1740  while ((clde = ReadDir(cldir, TWOPHASE_DIR)) != NULL)
1741  {
1742  if (strlen(clde->d_name) == 8 &&
1743  strspn(clde->d_name, "0123456789ABCDEF") == 8)
1744  {
1745  TransactionId xid;
1746  char *buf;
1747 
1748  xid = (TransactionId) strtoul(clde->d_name, NULL, 16);
1749 
1751  true, false, false);
1752  if (buf == NULL)
1753  continue;
1754 
1756  }
1757  }
1758  LWLockRelease(TwoPhaseStateLock);
1759  FreeDir(cldir);
1760 }
1761 
1762 /*
1763  * PrescanPreparedTransactions
1764  *
1765  * Scan the shared memory entries of TwoPhaseState and determine the range
1766  * of valid XIDs present. This is run during database startup, after we
1767  * have completed reading WAL. ShmemVariableCache->nextXid has been set to
1768  * one more than the highest XID for which evidence exists in WAL.
1769  *
1770  * We throw away any prepared xacts with main XID beyond nextXid --- if any
1771  * are present, it suggests that the DBA has done a PITR recovery to an
1772  * earlier point in time without cleaning out pg_twophase. We dare not
1773  * try to recover such prepared xacts since they likely depend on database
1774  * state that doesn't exist now.
1775  *
1776  * However, we will advance nextXid beyond any subxact XIDs belonging to
1777  * valid prepared xacts. We need to do this since subxact commit doesn't
1778  * write a WAL entry, and so there might be no evidence in WAL of those
1779  * subxact XIDs.
1780  *
1781  * Our other responsibility is to determine and return the oldest valid XID
1782  * among the prepared xacts (if none, return ShmemVariableCache->nextXid).
1783  * This is needed to synchronize pg_subtrans startup properly.
1784  *
1785  * If xids_p and nxids_p are not NULL, pointer to a palloc'd array of all
1786  * top-level xids is stored in *xids_p. The number of entries in the array
1787  * is returned in *nxids_p.
1788  */
1791 {
1792  TransactionId origNextXid = ShmemVariableCache->nextXid;
1793  TransactionId result = origNextXid;
1794  TransactionId *xids = NULL;
1795  int nxids = 0;
1796  int allocsize = 0;
1797  int i;
1798 
1799  LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
1800  for (i = 0; i < TwoPhaseState->numPrepXacts; i++)
1801  {
1802  TransactionId xid;
1803  char *buf;
1804  GlobalTransaction gxact = TwoPhaseState->prepXacts[i];
1805 
1806  Assert(gxact->inredo);
1807 
1808  xid = gxact->xid;
1809 
1810  buf = ProcessTwoPhaseBuffer(xid,
1811  gxact->prepare_start_lsn,
1812  gxact->ondisk, false, true);
1813 
1814  if (buf == NULL)
1815  continue;
1816 
1817  /*
1818  * OK, we think this file is valid. Incorporate xid into the
1819  * running-minimum result.
1820  */
1821  if (TransactionIdPrecedes(xid, result))
1822  result = xid;
1823 
1824  if (xids_p)
1825  {
1826  if (nxids == allocsize)
1827  {
1828  if (nxids == 0)
1829  {
1830  allocsize = 10;
1831  xids = palloc(allocsize * sizeof(TransactionId));
1832  }
1833  else
1834  {
1835  allocsize = allocsize * 2;
1836  xids = repalloc(xids, allocsize * sizeof(TransactionId));
1837  }
1838  }
1839  xids[nxids++] = xid;
1840  }
1841 
1842  pfree(buf);
1843  }
1844  LWLockRelease(TwoPhaseStateLock);
1845 
1846  if (xids_p)
1847  {
1848  *xids_p = xids;
1849  *nxids_p = nxids;
1850  }
1851 
1852  return result;
1853 }
1854 
1855 /*
1856  * StandbyRecoverPreparedTransactions
1857  *
1858  * Scan the shared memory entries of TwoPhaseState and setup all the required
1859  * information to allow standby queries to treat prepared transactions as still
1860  * active.
1861  *
1862  * This is never called at the end of recovery - we use
1863  * RecoverPreparedTransactions() at that point.
1864  *
1865  * The lack of calls to SubTransSetParent() calls here is by design;
1866  * those calls are made by RecoverPreparedTransactions() at the end of recovery
1867  * for those xacts that need this.
1868  */
1869 void
1871 {
1872  int i;
1873 
1874  LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
1875  for (i = 0; i < TwoPhaseState->numPrepXacts; i++)
1876  {
1877  TransactionId xid;
1878  char *buf;
1879  GlobalTransaction gxact = TwoPhaseState->prepXacts[i];
1880 
1881  Assert(gxact->inredo);
1882 
1883  xid = gxact->xid;
1884 
1885  buf = ProcessTwoPhaseBuffer(xid,
1886  gxact->prepare_start_lsn,
1887  gxact->ondisk, false, false);
1888  if (buf != NULL)
1889  pfree(buf);
1890  }
1891  LWLockRelease(TwoPhaseStateLock);
1892 }
1893 
1894 /*
1895  * RecoverPreparedTransactions
1896  *
1897  * Scan the shared memory entries of TwoPhaseState and reload the state for
1898  * each prepared transaction (reacquire locks, etc).
1899  *
1900  * This is run at the end of recovery, but before we allow backends to write
1901  * WAL.
1902  *
1903  * At the end of recovery the way we take snapshots will change. We now need
1904  * to mark all running transactions with their full SubTransSetParent() info
1905  * to allow normal snapshots to work correctly if snapshots overflow.
1906  * We do this here because by definition prepared transactions are the only
1907  * type of write transaction still running, so this is necessary and
1908  * complete.
1909  */
1910 void
1912 {
1913  int i;
1914 
1915  LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
1916  for (i = 0; i < TwoPhaseState->numPrepXacts; i++)
1917  {
1918  TransactionId xid;
1919  char *buf;
1920  GlobalTransaction gxact = TwoPhaseState->prepXacts[i];
1921  char *bufptr;
1922  TwoPhaseFileHeader *hdr;
1923  TransactionId *subxids;
1924  const char *gid;
1925 
1926  xid = gxact->xid;
1927 
1928  /*
1929  * Reconstruct subtrans state for the transaction --- needed because
1930  * pg_subtrans is not preserved over a restart. Note that we are
1931  * linking all the subtransactions directly to the top-level XID;
1932  * there may originally have been a more complex hierarchy, but
1933  * there's no need to restore that exactly. It's possible that
1934  * SubTransSetParent has been set before, if the prepared transaction
1935  * generated xid assignment records.
1936  */
1937  buf = ProcessTwoPhaseBuffer(xid,
1938  gxact->prepare_start_lsn,
1939  gxact->ondisk, true, false);
1940  if (buf == NULL)
1941  continue;
1942 
1943  ereport(LOG,
1944  (errmsg("recovering prepared transaction %u from shared memory", xid)));
1945 
1946  hdr = (TwoPhaseFileHeader *) buf;
1947  Assert(TransactionIdEquals(hdr->xid, xid));
1948  bufptr = buf + MAXALIGN(sizeof(TwoPhaseFileHeader));
1949  gid = (const char *) bufptr;
1950  bufptr += MAXALIGN(hdr->gidlen);
1951  subxids = (TransactionId *) bufptr;
1952  bufptr += MAXALIGN(hdr->nsubxacts * sizeof(TransactionId));
1953  bufptr += MAXALIGN(hdr->ncommitrels * sizeof(RelFileNode));
1954  bufptr += MAXALIGN(hdr->nabortrels * sizeof(RelFileNode));
1955  bufptr += MAXALIGN(hdr->ninvalmsgs * sizeof(SharedInvalidationMessage));
1956 
1957  /*
1958  * Recreate its GXACT and dummy PGPROC. But, check whether it was
1959  * added in redo and already has a shmem entry for it.
1960  */
1961  MarkAsPreparingGuts(gxact, xid, gid,
1962  hdr->prepared_at,
1963  hdr->owner, hdr->database);
1964 
1965  /* recovered, so reset the flag for entries generated by redo */
1966  gxact->inredo = false;
1967 
1968  GXactLoadSubxactData(gxact, hdr->nsubxacts, subxids);
1969  MarkAsPrepared(gxact, true);
1970 
1971  LWLockRelease(TwoPhaseStateLock);
1972 
1973  /*
1974  * Recover other state (notably locks) using resource managers.
1975  */
1977 
1978  /*
1979  * Release locks held by the standby process after we process each
1980  * prepared transaction. As a result, we don't need too many
1981  * additional locks at any one time.
1982  */
1983  if (InHotStandby)
1984  StandbyReleaseLockTree(xid, hdr->nsubxacts, subxids);
1985 
1986  /*
1987  * We're done with recovering this transaction. Clear MyLockedGxact,
1988  * like we do in PrepareTransaction() during normal operation.
1989  */
1991 
1992  pfree(buf);
1993 
1994  LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
1995  }
1996 
1997  LWLockRelease(TwoPhaseStateLock);
1998 }
1999 
2000 /*
2001  * ProcessTwoPhaseBuffer
2002  *
2003  * Given a transaction id, read it either from disk or read it directly
2004  * via shmem xlog record pointer using the provided "prepare_start_lsn".
2005  *
2006  * If setParent is true, set up subtransaction parent linkages.
2007  *
2008  * If setNextXid is true, set ShmemVariableCache->nextXid to the newest
2009  * value scanned.
2010  */
2011 static char *
2013  XLogRecPtr prepare_start_lsn,
2014  bool fromdisk,
2015  bool setParent, bool setNextXid)
2016 {
2017  TransactionId origNextXid = ShmemVariableCache->nextXid;
2018  TransactionId *subxids;
2019  char *buf;
2020  TwoPhaseFileHeader *hdr;
2021  int i;
2022 
2023  Assert(LWLockHeldByMeInMode(TwoPhaseStateLock, LW_EXCLUSIVE));
2024 
2025  if (!fromdisk)
2026  Assert(prepare_start_lsn != InvalidXLogRecPtr);
2027 
2028  /* Already processed? */
2030  {
2031  if (fromdisk)
2032  {
2033  ereport(WARNING,
2034  (errmsg("removing stale two-phase state file for \"%u\"",
2035  xid)));
2036  RemoveTwoPhaseFile(xid, true);
2037  }
2038  else
2039  {
2040  ereport(WARNING,
2041  (errmsg("removing stale two-phase state from shared memory for \"%u\"",
2042  xid)));
2043  PrepareRedoRemove(xid, true);
2044  }
2045  return NULL;
2046  }
2047 
2048  /* Reject XID if too new */
2049  if (TransactionIdFollowsOrEquals(xid, origNextXid))
2050  {
2051  if (fromdisk)
2052  {
2053  ereport(WARNING,
2054  (errmsg("removing future two-phase state file for \"%u\"",
2055  xid)));
2056  RemoveTwoPhaseFile(xid, true);
2057  }
2058  else
2059  {
2060  ereport(WARNING,
2061  (errmsg("removing future two-phase state from memory for \"%u\"",
2062  xid)));
2063  PrepareRedoRemove(xid, true);
2064  }
2065  return NULL;
2066  }
2067 
2068  if (fromdisk)
2069  {
2070  /* Read and validate file */
2071  buf = ReadTwoPhaseFile(xid, true);
2072  if (buf == NULL)
2073  {
2074  ereport(WARNING,
2075  (errmsg("removing corrupt two-phase state file for \"%u\"",
2076  xid)));
2077  RemoveTwoPhaseFile(xid, true);
2078  return NULL;
2079  }
2080  }
2081  else
2082  {
2083  /* Read xlog data */
2084  XlogReadTwoPhaseData(prepare_start_lsn, &buf, NULL);
2085  }
2086 
2087  /* Deconstruct header */
2088  hdr = (TwoPhaseFileHeader *) buf;
2089  if (!TransactionIdEquals(hdr->xid, xid))
2090  {
2091  if (fromdisk)
2092  {
2093  ereport(WARNING,
2094  (errmsg("removing corrupt two-phase state file for \"%u\"",
2095  xid)));
2096  RemoveTwoPhaseFile(xid, true);
2097  }
2098  else
2099  {
2100  ereport(WARNING,
2101  (errmsg("removing corrupt two-phase state from memory for \"%u\"",
2102  xid)));
2103  PrepareRedoRemove(xid, true);
2104  }
2105  pfree(buf);
2106  return NULL;
2107  }
2108 
2109  /*
2110  * Examine subtransaction XIDs ... they should all follow main XID, and
2111  * they may force us to advance nextXid.
2112  */
2113  subxids = (TransactionId *) (buf +
2114  MAXALIGN(sizeof(TwoPhaseFileHeader)) +
2115  MAXALIGN(hdr->gidlen));
2116  for (i = 0; i < hdr->nsubxacts; i++)
2117  {
2118  TransactionId subxid = subxids[i];
2119 
2120  Assert(TransactionIdFollows(subxid, xid));
2121 
2122  /* update nextXid if needed */
2123  if (setNextXid &&
2126  {
2127  /*
2128  * We don't expect anyone else to modify nextXid, hence we don't
2129  * need to hold a lock while examining it. We still acquire the
2130  * lock to modify it, though, so we recheck.
2131  */
2132  LWLockAcquire(XidGenLock, LW_EXCLUSIVE);
2133  if (TransactionIdFollowsOrEquals(subxid,
2135  {
2136  ShmemVariableCache->nextXid = subxid;
2138  }
2139  LWLockRelease(XidGenLock);
2140  }
2141 
2142  if (setParent)
2143  SubTransSetParent(subxid, xid);
2144  }
2145 
2146  return buf;
2147 }
2148 
2149 
2150 /*
2151  * RecordTransactionCommitPrepared
2152  *
2153  * This is basically the same as RecordTransactionCommit (q.v. if you change
2154  * this function): in particular, we must set the delayChkpt flag to avoid a
2155  * race condition.
2156  *
2157  * We know the transaction made at least one XLOG entry (its PREPARE),
2158  * so it is never possible to optimize out the commit record.
2159  */
2160 static void
2162  int nchildren,
2163  TransactionId *children,
2164  int nrels,
2165  RelFileNode *rels,
2166  int ninvalmsgs,
2167  SharedInvalidationMessage *invalmsgs,
2168  bool initfileinval)
2169 {
2170  XLogRecPtr recptr;
2171  TimestampTz committs = GetCurrentTimestamp();
2172  bool replorigin;
2173 
2174  /*
2175  * Are we using the replication origins feature? Or, in other words, are
2176  * we replaying remote actions?
2177  */
2178  replorigin = (replorigin_session_origin != InvalidRepOriginId &&
2180 
2182 
2183  /* See notes in RecordTransactionCommit */
2184  MyPgXact->delayChkpt = true;
2185 
2186  /*
2187  * Emit the XLOG commit record. Note that we mark 2PC commits as
2188  * potentially having AccessExclusiveLocks since we don't know whether or
2189  * not they do.
2190  */
2191  recptr = XactLogCommitRecord(committs,
2192  nchildren, children, nrels, rels,
2193  ninvalmsgs, invalmsgs,
2194  initfileinval, false,
2196  xid);
2197 
2198 
2199  if (replorigin)
2200  /* Move LSNs forward for this replication origin */
2202  XactLastRecEnd);
2203 
2204  /*
2205  * Record commit timestamp. The value comes from plain commit timestamp
2206  * if replorigin is not enabled, or replorigin already set a value for us
2207  * in replorigin_session_origin_timestamp otherwise.
2208  *
2209  * We don't need to WAL-log anything here, as the commit record written
2210  * above already contains the data.
2211  */
2212  if (!replorigin || replorigin_session_origin_timestamp == 0)
2214 
2215  TransactionTreeSetCommitTsData(xid, nchildren, children,
2217  replorigin_session_origin, false);
2218 
2219  /*
2220  * We don't currently try to sleep before flush here ... nor is there any
2221  * support for async commit of a prepared xact (the very idea is probably
2222  * a contradiction)
2223  */
2224 
2225  /* Flush XLOG to disk */
2226  XLogFlush(recptr);
2227 
2228  /* Mark the transaction committed in pg_xact */
2229  TransactionIdCommitTree(xid, nchildren, children);
2230 
2231  /* Checkpoint can proceed now */
2232  MyPgXact->delayChkpt = false;
2233 
2234  END_CRIT_SECTION();
2235 
2236  /*
2237  * Wait for synchronous replication, if required.
2238  *
2239  * Note that at this stage we have marked clog, but still show as running
2240  * in the procarray and continue to hold locks.
2241  */
2242  SyncRepWaitForLSN(recptr, true);
2243 }
2244 
2245 /*
2246  * RecordTransactionAbortPrepared
2247  *
2248  * This is basically the same as RecordTransactionAbort.
2249  *
2250  * We know the transaction made at least one XLOG entry (its PREPARE),
2251  * so it is never possible to optimize out the abort record.
2252  */
2253 static void
2255  int nchildren,
2256  TransactionId *children,
2257  int nrels,
2258  RelFileNode *rels)
2259 {
2260  XLogRecPtr recptr;
2261 
2262  /*
2263  * Catch the scenario where we aborted partway through
2264  * RecordTransactionCommitPrepared ...
2265  */
2266  if (TransactionIdDidCommit(xid))
2267  elog(PANIC, "cannot abort transaction %u, it was already committed",
2268  xid);
2269 
2271 
2272  /*
2273  * Emit the XLOG commit record. Note that we mark 2PC aborts as
2274  * potentially having AccessExclusiveLocks since we don't know whether or
2275  * not they do.
2276  */
2278  nchildren, children,
2279  nrels, rels,
2281  xid);
2282 
2283  /* Always flush, since we're about to remove the 2PC state file */
2284  XLogFlush(recptr);
2285 
2286  /*
2287  * Mark the transaction aborted in clog. This is not absolutely necessary
2288  * but we may as well do it while we are here.
2289  */
2290  TransactionIdAbortTree(xid, nchildren, children);
2291 
2292  END_CRIT_SECTION();
2293 
2294  /*
2295  * Wait for synchronous replication, if required.
2296  *
2297  * Note that at this stage we have marked clog, but still show as running
2298  * in the procarray and continue to hold locks.
2299  */
2300  SyncRepWaitForLSN(recptr, false);
2301 }
2302 
2303 /*
2304  * PrepareRedoAdd
2305  *
2306  * Store pointers to the start/end of the WAL record along with the xid in
2307  * a gxact entry in shared memory TwoPhaseState structure. If caller
2308  * specifies InvalidXLogRecPtr as WAL location to fetch the two-phase
2309  * data, the entry is marked as located on disk.
2310  */
2311 void
2312 PrepareRedoAdd(char *buf, XLogRecPtr start_lsn, XLogRecPtr end_lsn)
2313 {
2314  TwoPhaseFileHeader *hdr = (TwoPhaseFileHeader *) buf;
2315  char *bufptr;
2316  const char *gid;
2317  GlobalTransaction gxact;
2318 
2319  Assert(LWLockHeldByMeInMode(TwoPhaseStateLock, LW_EXCLUSIVE));
2321 
2322  bufptr = buf + MAXALIGN(sizeof(TwoPhaseFileHeader));
2323  gid = (const char *) bufptr;
2324 
2325  /*
2326  * Reserve the GID for the given transaction in the redo code path.
2327  *
2328  * This creates a gxact struct and puts it into the active array.
2329  *
2330  * In redo, this struct is mainly used to track PREPARE/COMMIT entries in
2331  * shared memory. Hence, we only fill up the bare minimum contents here.
2332  * The gxact also gets marked with gxact->inredo set to true to indicate
2333  * that it got added in the redo phase
2334  */
2335 
2336  /* Get a free gxact from the freelist */
2337  if (TwoPhaseState->freeGXacts == NULL)
2338  ereport(ERROR,
2339  (errcode(ERRCODE_OUT_OF_MEMORY),
2340  errmsg("maximum number of prepared transactions reached"),
2341  errhint("Increase max_prepared_transactions (currently %d).",
2342  max_prepared_xacts)));
2343  gxact = TwoPhaseState->freeGXacts;
2344  TwoPhaseState->freeGXacts = gxact->next;
2345 
2346  gxact->prepared_at = hdr->prepared_at;
2347  gxact->prepare_start_lsn = start_lsn;
2348  gxact->prepare_end_lsn = end_lsn;
2349  gxact->xid = hdr->xid;
2350  gxact->owner = hdr->owner;
2352  gxact->valid = false;
2353  gxact->ondisk = XLogRecPtrIsInvalid(start_lsn);
2354  gxact->inredo = true; /* yes, added in redo */
2355  strcpy(gxact->gid, gid);
2356 
2357  /* And insert it into the active array */
2358  Assert(TwoPhaseState->numPrepXacts < max_prepared_xacts);
2359  TwoPhaseState->prepXacts[TwoPhaseState->numPrepXacts++] = gxact;
2360 
2361  elog(DEBUG2, "added 2PC data in shared memory for transaction %u", gxact->xid);
2362 }
2363 
2364 /*
2365  * PrepareRedoRemove
2366  *
2367  * Remove the corresponding gxact entry from TwoPhaseState. Also remove
2368  * the 2PC file if a prepared transaction was saved via an earlier checkpoint.
2369  *
2370  * Caller must hold TwoPhaseStateLock in exclusive mode, because TwoPhaseState
2371  * is updated.
2372  */
2373 void
2374 PrepareRedoRemove(TransactionId xid, bool giveWarning)
2375 {
2376  GlobalTransaction gxact = NULL;
2377  int i;
2378  bool found = false;
2379 
2380  Assert(LWLockHeldByMeInMode(TwoPhaseStateLock, LW_EXCLUSIVE));
2382 
2383  for (i = 0; i < TwoPhaseState->numPrepXacts; i++)
2384  {
2385  gxact = TwoPhaseState->prepXacts[i];
2386 
2387  if (gxact->xid == xid)
2388  {
2389  Assert(gxact->inredo);
2390  found = true;
2391  break;
2392  }
2393  }
2394 
2395  /*
2396  * Just leave if there is nothing, this is expected during WAL replay.
2397  */
2398  if (!found)
2399  return;
2400 
2401  /*
2402  * And now we can clean up any files we may have left.
2403  */
2404  elog(DEBUG2, "removing 2PC data for transaction %u", xid);
2405  if (gxact->ondisk)
2406  RemoveTwoPhaseFile(xid, giveWarning);
2407  RemoveGXact(gxact);
2408 
2409  return;
2410 }
#define TransactionIdAdvance(dest)
Definition: transam.h:48
#define TIMESTAMPTZOID
Definition: pg_type.h:525
void TransactionIdAbortTree(TransactionId xid, int nxids, TransactionId *xids)
Definition: transam.c:290
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Datum pg_prepared_xact(PG_FUNCTION_ARGS)
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#define InvalidXLogRecPtr
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#define TWOPHASE_RM_MAX_ID
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static void RecordTransactionAbortPrepared(TransactionId xid, int nchildren, TransactionId *children, int nrels, RelFileNode *rels)
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struct TwoPhaseRecordOnDisk TwoPhaseRecordOnDisk
XLogRecPtr XactLogAbortRecord(TimestampTz abort_time, int nsubxacts, TransactionId *subxacts, int nrels, RelFileNode *rels, int xactflags, TransactionId twophase_xid)
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Definition: origin.c:157
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Definition: superuser.c:57
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static struct xllist records
static void RecreateTwoPhaseFile(TransactionId xid, void *content, int len)
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Definition: xact.c:118
static void RecordTransactionCommitPrepared(TransactionId xid, int nchildren, TransactionId *children, int nrels, RelFileNode *rels, int ninvalmsgs, SharedInvalidationMessage *invalmsgs, bool initfileinval)
Definition: twophase.c:2161
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Definition: twophase.c:950
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Definition: fd.c:2305
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const TwoPhaseCallback twophase_postabort_callbacks[TWOPHASE_RM_MAX_ID+1]
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Size add_size(Size s1, Size s2)
Definition: shmem.c:475
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Definition: backendid.h:21
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Definition: globals.c:77
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Definition: relcache.c:6075
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Definition: twophase.c:1549
#define PGPROC_MAX_CACHED_SUBXIDS
Definition: proc.h:35
#define TWOPHASE_MAGIC
Definition: twophase.c:901
void FinishPreparedTransaction(const char *gid, bool isCommit)
Definition: twophase.c:1367
struct GlobalTransactionData GlobalTransactionData
#define Max(x, y)
Definition: c.h:801
TransactionId xids[PGPROC_MAX_CACHED_SUBXIDS]
Definition: proc.h:39
StateFileChunk * head
Definition: twophase.c:946
#define NULL
Definition: c.h:229
void RelationCacheInitFilePreInvalidate(void)
Definition: relcache.c:6049
uint64 XLogRecPtr
Definition: xlogdefs.h:21
#define Assert(condition)
Definition: c.h:676
RepOriginId replorigin_session_origin
Definition: origin.c:155
struct dirent * ReadDir(DIR *dir, const char *dirname)
Definition: fd.c:2401
void EndPrepare(GlobalTransaction gxact)
Definition: twophase.c:1064
MemoryContext multi_call_memory_ctx
Definition: funcapi.h:109
size_t Size
Definition: c.h:356
static void pgstat_report_wait_start(uint32 wait_event_info)
Definition: pgstat.h:1211
void XLogEnsureRecordSpace(int max_block_id, int ndatas)
Definition: xloginsert.c:146
void replorigin_session_advance(XLogRecPtr remote_commit, XLogRecPtr local_commit)
Definition: origin.c:1127
#define XLOG_XACT_OPMASK
Definition: xact.h:143
bool LWLockAcquire(LWLock *lock, LWLockMode mode)
Definition: lwlock.c:1111
#define MAXALIGN(LEN)
Definition: c.h:588
#define GIDSIZE
Definition: twophase.c:151
#define HeapTupleGetDatum(tuple)
Definition: funcapi.h:222
void SendSharedInvalidMessages(const SharedInvalidationMessage *msgs, int n)
Definition: sinval.c:49
static void save_state_data(const void *data, uint32 len)
Definition: twophase.c:963
TupleDesc CreateTemplateTupleDesc(int natts, bool hasoid)
Definition: tupdesc.c:41
void * repalloc(void *pointer, Size size)
Definition: mcxt.c:963
static void MarkAsPrepared(GlobalTransaction gxact, bool lock_held)
Definition: twophase.c:537
#define InvalidRepOriginId
Definition: origin.h:34
#define TWOPHASE_DIR
Definition: twophase.c:114
TransactionId xid
Definition: twophase.c:169
static Datum values[MAXATTR]
Definition: bootstrap.c:163
TimestampTz prepared_at
Definition: twophase.c:158
void SHMQueueElemInit(SHM_QUEUE *queue)
Definition: shmqueue.c:57
static void XlogReadTwoPhaseData(XLogRecPtr lsn, char **buf, int *len)
Definition: twophase.c:1296
int pgprocno
Definition: proc.h:109
static char * user
Definition: pg_regress.c:92
void * user_fctx
Definition: funcapi.h:90
void restoreTwoPhaseData(void)
Definition: twophase.c:1733
void * palloc(Size size)
Definition: mcxt.c:849
int errmsg(const char *fmt,...)
Definition: elog.c:797
void SHMQueueInit(SHM_QUEUE *queue)
Definition: shmqueue.c:36
int xactGetCommittedInvalidationMessages(SharedInvalidationMessage **msgs, bool *RelcacheInitFileInval)
Definition: inval.c:816
static GlobalTransaction MyLockedGxact
Definition: twophase.c:203
void PostPrepare_Twophase(void)
Definition: twophase.c:359
int i
#define CStringGetTextDatum(s)
Definition: builtins.h:91
void * arg
#define PG_FUNCTION_ARGS
Definition: fmgr.h:158
PGPROC * allProcs
Definition: proc.h:232
int pg_fsync(int fd)
Definition: fd.c:333
void CheckPointTwoPhase(XLogRecPtr redo_horizon)
Definition: twophase.c:1651
SHM_QUEUE myProcLocks[NUM_LOCK_PARTITIONS]
Definition: proc.h:156
char d_name[MAX_PATH]
Definition: dirent.h:14
#define elog
Definition: elog.h:219
TimestampTz prepared_at
Definition: twophase.c:909
#define TransactionIdIsValid(xid)
Definition: transam.h:41
void StandbyRecoverPreparedTransactions(void)
Definition: twophase.c:1870
static void static void status(const char *fmt,...) pg_attribute_printf(1
Definition: pg_regress.c:224
static void AtProcExit_Twophase(int code, Datum arg)
Definition: twophase.c:309
void SubTransSetParent(TransactionId xid, TransactionId parent)
Definition: subtrans.c:74
#define COMP_CRC32C(crc, data, len)
Definition: pg_crc32c.h:73
void RecoverPreparedTransactions(void)
Definition: twophase.c:1911
void XLogBeginInsert(void)
Definition: xloginsert.c:120
void TransactionTreeSetCommitTsData(TransactionId xid, int nsubxids, TransactionId *subxids, TimestampTz timestamp, RepOriginId nodeid, bool write_xlog)
Definition: commit_ts.c:145
#define ERRCODE_DUPLICATE_OBJECT
Definition: streamutil.c:32
Definition: proc.h:94
#define FIN_CRC32C(crc)
Definition: pg_crc32c.h:78
int pid
Definition: proc.h:108
int16 AttrNumber
Definition: attnum.h:21
XLogRecPtr prepare_end_lsn
Definition: twophase.c:168
void ProcArrayAdd(PGPROC *proc)
Definition: procarray.c:275
#define read(a, b, c)
Definition: win32.h:13
int FreeDir(DIR *dir)
Definition: fd.c:2444
#define offsetof(type, field)
Definition: c.h:555
BackendId dummyBackendId
Definition: twophase.c:157
#define NUM_LOCK_PARTITIONS
Definition: lwlock.h:117
#define XLogRecGetRmid(decoder)
Definition: xlogreader.h:217
void AtEOXact_PgStat(bool isCommit)
Definition: pgstat.c:2053
#define SRF_RETURN_DONE(_funcctx)
Definition: funcapi.h:309
LocalTransactionId lxid
Definition: proc.h:105
#define SRF_FIRSTCALL_INIT()
Definition: funcapi.h:287
TwoPhaseRmgrId rmid
Definition: twophase.c:928