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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) 1996-2019, 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/xlogreader.h"
89 #include "access/xlogutils.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/md.h"
102 #include "storage/predicate.h"
103 #include "storage/proc.h"
104 #include "storage/procarray.h"
105 #include "storage/sinvaladt.h"
106 #include "storage/smgr.h"
107 #include "utils/builtins.h"
108 #include "utils/memutils.h"
109 #include "utils/timestamp.h"
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 
149 typedef struct GlobalTransactionData
150 {
151  GlobalTransaction next; /* list link for free list */
152  int pgprocno; /* ID of associated dummy PGPROC */
153  BackendId dummyBackendId; /* similar to backend id for backends */
154  TimestampTz prepared_at; /* time of preparation */
155 
156  /*
157  * Note that we need to keep track of two LSNs for each GXACT. We keep
158  * track of the start LSN because this is the address we must use to read
159  * state data back from WAL when committing a prepared GXACT. We keep
160  * track of the end LSN because that is the LSN we need to wait for prior
161  * to commit.
162  */
163  XLogRecPtr prepare_start_lsn; /* XLOG offset of prepare record start */
164  XLogRecPtr prepare_end_lsn; /* XLOG offset of prepare record end */
165  TransactionId xid; /* The GXACT id */
166 
167  Oid owner; /* ID of user that executed the xact */
168  BackendId locking_backend; /* backend currently working on the xact */
169  bool valid; /* true if PGPROC entry is in proc array */
170  bool ondisk; /* true if prepare state file is on disk */
171  bool inredo; /* true if entry was added via xlog_redo */
172  char gid[GIDSIZE]; /* The GID assigned to the prepared xact */
174 
175 /*
176  * Two Phase Commit shared state. Access to this struct is protected
177  * by TwoPhaseStateLock.
178  */
179 typedef struct TwoPhaseStateData
180 {
181  /* Head of linked list of free GlobalTransactionData structs */
183 
184  /* Number of valid prepXacts entries. */
186 
187  /* There are max_prepared_xacts items in this array */
188  GlobalTransaction prepXacts[FLEXIBLE_ARRAY_MEMBER];
190 
192 
193 /*
194  * Global transaction entry currently locked by us, if any. Note that any
195  * access to the entry pointed to by this variable must be protected by
196  * TwoPhaseStateLock, though obviously the pointer itself doesn't need to be
197  * (since it's just local memory).
198  */
200 
201 static bool twophaseExitRegistered = false;
202 
204  int nchildren,
205  TransactionId *children,
206  int nrels,
207  RelFileNode *rels,
208  int ninvalmsgs,
209  SharedInvalidationMessage *invalmsgs,
210  bool initfileinval,
211  const char *gid);
213  int nchildren,
214  TransactionId *children,
215  int nrels,
216  RelFileNode *rels,
217  const char *gid);
218 static void ProcessRecords(char *bufptr, TransactionId xid,
219  const TwoPhaseCallback callbacks[]);
220 static void RemoveGXact(GlobalTransaction gxact);
221 
222 static void XlogReadTwoPhaseData(XLogRecPtr lsn, char **buf, int *len);
225  bool fromdisk, bool setParent, bool setNextXid);
227  const char *gid, TimestampTz prepared_at, Oid owner,
228  Oid databaseid);
229 static void RemoveTwoPhaseFile(TransactionId xid, bool giveWarning);
230 static void RecreateTwoPhaseFile(TransactionId xid, void *content, int len);
231 
232 /*
233  * Initialization of shared memory
234  */
235 Size
237 {
238  Size size;
239 
240  /* Need the fixed struct, the array of pointers, and the GTD structs */
241  size = offsetof(TwoPhaseStateData, prepXacts);
242  size = add_size(size, mul_size(max_prepared_xacts,
243  sizeof(GlobalTransaction)));
244  size = MAXALIGN(size);
245  size = add_size(size, mul_size(max_prepared_xacts,
246  sizeof(GlobalTransactionData)));
247 
248  return size;
249 }
250 
251 void
253 {
254  bool found;
255 
256  TwoPhaseState = ShmemInitStruct("Prepared Transaction Table",
258  &found);
259  if (!IsUnderPostmaster)
260  {
261  GlobalTransaction gxacts;
262  int i;
263 
264  Assert(!found);
265  TwoPhaseState->freeGXacts = NULL;
266  TwoPhaseState->numPrepXacts = 0;
267 
268  /*
269  * Initialize the linked list of free GlobalTransactionData structs
270  */
271  gxacts = (GlobalTransaction)
272  ((char *) TwoPhaseState +
273  MAXALIGN(offsetof(TwoPhaseStateData, prepXacts) +
275  for (i = 0; i < max_prepared_xacts; i++)
276  {
277  /* insert into linked list */
278  gxacts[i].next = TwoPhaseState->freeGXacts;
279  TwoPhaseState->freeGXacts = &gxacts[i];
280 
281  /* associate it with a PGPROC assigned by InitProcGlobal */
283 
284  /*
285  * Assign a unique ID for each dummy proc, so that the range of
286  * dummy backend IDs immediately follows the range of normal
287  * backend IDs. We don't dare to assign a real backend ID to dummy
288  * procs, because prepared transactions don't take part in cache
289  * invalidation like a real backend ID would imply, but having a
290  * unique ID for them is nevertheless handy. This arrangement
291  * allows you to allocate an array of size (MaxBackends +
292  * max_prepared_xacts + 1), and have a slot for every backend and
293  * prepared transaction. Currently multixact.c uses that
294  * technique.
295  */
296  gxacts[i].dummyBackendId = MaxBackends + 1 + i;
297  }
298  }
299  else
300  Assert(found);
301 }
302 
303 /*
304  * Exit hook to unlock the global transaction entry we're working on.
305  */
306 static void
308 {
309  /* same logic as abort */
311 }
312 
313 /*
314  * Abort hook to unlock the global transaction entry we're working on.
315  */
316 void
318 {
319  if (MyLockedGxact == NULL)
320  return;
321 
322  /*
323  * What to do with the locked global transaction entry? If we were in the
324  * process of preparing the transaction, but haven't written the WAL
325  * record and state file yet, the transaction must not be considered as
326  * prepared. Likewise, if we are in the process of finishing an
327  * already-prepared transaction, and fail after having already written the
328  * 2nd phase commit or rollback record to the WAL, the transaction should
329  * not be considered as prepared anymore. In those cases, just remove the
330  * entry from shared memory.
331  *
332  * Otherwise, the entry must be left in place so that the transaction can
333  * be finished later, so just unlock it.
334  *
335  * If we abort during prepare, after having written the WAL record, we
336  * might not have transferred all locks and other state to the prepared
337  * transaction yet. Likewise, if we abort during commit or rollback,
338  * after having written the WAL record, we might not have released all the
339  * resources held by the transaction yet. In those cases, the in-memory
340  * state can be wrong, but it's too late to back out.
341  */
342  LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
343  if (!MyLockedGxact->valid)
344  RemoveGXact(MyLockedGxact);
345  else
346  MyLockedGxact->locking_backend = InvalidBackendId;
347  LWLockRelease(TwoPhaseStateLock);
348 
349  MyLockedGxact = NULL;
350 }
351 
352 /*
353  * This is called after we have finished transferring state to the prepared
354  * PGXACT entry.
355  */
356 void
358 {
359  LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
360  MyLockedGxact->locking_backend = InvalidBackendId;
361  LWLockRelease(TwoPhaseStateLock);
362 
363  MyLockedGxact = NULL;
364 }
365 
366 
367 /*
368  * MarkAsPreparing
369  * Reserve the GID for the given transaction.
370  */
373  TimestampTz prepared_at, Oid owner, Oid databaseid)
374 {
375  GlobalTransaction gxact;
376  int i;
377 
378  if (strlen(gid) >= GIDSIZE)
379  ereport(ERROR,
380  (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
381  errmsg("transaction identifier \"%s\" is too long",
382  gid)));
383 
384  /* fail immediately if feature is disabled */
385  if (max_prepared_xacts == 0)
386  ereport(ERROR,
387  (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
388  errmsg("prepared transactions are disabled"),
389  errhint("Set max_prepared_transactions to a nonzero value.")));
390 
391  /* on first call, register the exit hook */
393  {
395  twophaseExitRegistered = true;
396  }
397 
398  LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
399 
400  /* Check for conflicting GID */
401  for (i = 0; i < TwoPhaseState->numPrepXacts; i++)
402  {
403  gxact = TwoPhaseState->prepXacts[i];
404  if (strcmp(gxact->gid, gid) == 0)
405  {
406  ereport(ERROR,
408  errmsg("transaction identifier \"%s\" is already in use",
409  gid)));
410  }
411  }
412 
413  /* Get a free gxact from the freelist */
414  if (TwoPhaseState->freeGXacts == NULL)
415  ereport(ERROR,
416  (errcode(ERRCODE_OUT_OF_MEMORY),
417  errmsg("maximum number of prepared transactions reached"),
418  errhint("Increase max_prepared_transactions (currently %d).",
420  gxact = TwoPhaseState->freeGXacts;
421  TwoPhaseState->freeGXacts = gxact->next;
422 
423  MarkAsPreparingGuts(gxact, xid, gid, prepared_at, owner, databaseid);
424 
425  gxact->ondisk = false;
426 
427  /* And insert it into the active array */
428  Assert(TwoPhaseState->numPrepXacts < max_prepared_xacts);
429  TwoPhaseState->prepXacts[TwoPhaseState->numPrepXacts++] = gxact;
430 
431  LWLockRelease(TwoPhaseStateLock);
432 
433  return gxact;
434 }
435 
436 /*
437  * MarkAsPreparingGuts
438  *
439  * This uses a gxact struct and puts it into the active array.
440  * NOTE: this is also used when reloading a gxact after a crash; so avoid
441  * assuming that we can use very much backend context.
442  *
443  * Note: This function should be called with appropriate locks held.
444  */
445 static void
447  TimestampTz prepared_at, Oid owner, Oid databaseid)
448 {
449  PGPROC *proc;
450  PGXACT *pgxact;
451  int i;
452 
453  Assert(LWLockHeldByMeInMode(TwoPhaseStateLock, LW_EXCLUSIVE));
454 
455  Assert(gxact != NULL);
456  proc = &ProcGlobal->allProcs[gxact->pgprocno];
457  pgxact = &ProcGlobal->allPgXact[gxact->pgprocno];
458 
459  /* Initialize the PGPROC entry */
460  MemSet(proc, 0, sizeof(PGPROC));
461  proc->pgprocno = gxact->pgprocno;
462  SHMQueueElemInit(&(proc->links));
463  proc->waitStatus = STATUS_OK;
464  /* We set up the gxact's VXID as InvalidBackendId/XID */
465  proc->lxid = (LocalTransactionId) xid;
466  pgxact->xid = xid;
467  pgxact->xmin = InvalidTransactionId;
468  pgxact->delayChkpt = false;
469  pgxact->vacuumFlags = 0;
470  proc->pid = 0;
471  proc->backendId = InvalidBackendId;
472  proc->databaseId = databaseid;
473  proc->roleId = owner;
474  proc->tempNamespaceId = InvalidOid;
475  proc->isBackgroundWorker = false;
476  proc->lwWaiting = false;
477  proc->lwWaitMode = 0;
478  proc->waitLock = NULL;
479  proc->waitProcLock = NULL;
480  for (i = 0; i < NUM_LOCK_PARTITIONS; i++)
481  SHMQueueInit(&(proc->myProcLocks[i]));
482  /* subxid data must be filled later by GXactLoadSubxactData */
483  pgxact->overflowed = false;
484  pgxact->nxids = 0;
485 
486  gxact->prepared_at = prepared_at;
487  gxact->xid = xid;
488  gxact->owner = owner;
489  gxact->locking_backend = MyBackendId;
490  gxact->valid = false;
491  gxact->inredo = false;
492  strcpy(gxact->gid, gid);
493 
494  /*
495  * Remember that we have this GlobalTransaction entry locked for us. If we
496  * abort after this, we must release it.
497  */
498  MyLockedGxact = gxact;
499 }
500 
501 /*
502  * GXactLoadSubxactData
503  *
504  * If the transaction being persisted had any subtransactions, this must
505  * be called before MarkAsPrepared() to load information into the dummy
506  * PGPROC.
507  */
508 static void
510  TransactionId *children)
511 {
512  PGPROC *proc = &ProcGlobal->allProcs[gxact->pgprocno];
513  PGXACT *pgxact = &ProcGlobal->allPgXact[gxact->pgprocno];
514 
515  /* We need no extra lock since the GXACT isn't valid yet */
516  if (nsubxacts > PGPROC_MAX_CACHED_SUBXIDS)
517  {
518  pgxact->overflowed = true;
519  nsubxacts = PGPROC_MAX_CACHED_SUBXIDS;
520  }
521  if (nsubxacts > 0)
522  {
523  memcpy(proc->subxids.xids, children,
524  nsubxacts * sizeof(TransactionId));
525  pgxact->nxids = nsubxacts;
526  }
527 }
528 
529 /*
530  * MarkAsPrepared
531  * Mark the GXACT as fully valid, and enter it into the global ProcArray.
532  *
533  * lock_held indicates whether caller already holds TwoPhaseStateLock.
534  */
535 static void
536 MarkAsPrepared(GlobalTransaction gxact, bool lock_held)
537 {
538  /* Lock here may be overkill, but I'm not convinced of that ... */
539  if (!lock_held)
540  LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
541  Assert(!gxact->valid);
542  gxact->valid = true;
543  if (!lock_held)
544  LWLockRelease(TwoPhaseStateLock);
545 
546  /*
547  * Put it into the global ProcArray so TransactionIdIsInProgress considers
548  * the XID as still running.
549  */
551 }
552 
553 /*
554  * LockGXact
555  * Locate the prepared transaction and mark it busy for COMMIT or PREPARE.
556  */
557 static GlobalTransaction
558 LockGXact(const char *gid, Oid user)
559 {
560  int i;
561 
562  /* on first call, register the exit hook */
564  {
566  twophaseExitRegistered = true;
567  }
568 
569  LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
570 
571  for (i = 0; i < TwoPhaseState->numPrepXacts; i++)
572  {
573  GlobalTransaction gxact = TwoPhaseState->prepXacts[i];
574  PGPROC *proc = &ProcGlobal->allProcs[gxact->pgprocno];
575 
576  /* Ignore not-yet-valid GIDs */
577  if (!gxact->valid)
578  continue;
579  if (strcmp(gxact->gid, gid) != 0)
580  continue;
581 
582  /* Found it, but has someone else got it locked? */
583  if (gxact->locking_backend != InvalidBackendId)
584  ereport(ERROR,
585  (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
586  errmsg("prepared transaction with identifier \"%s\" is busy",
587  gid)));
588 
589  if (user != gxact->owner && !superuser_arg(user))
590  ereport(ERROR,
591  (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
592  errmsg("permission denied to finish prepared transaction"),
593  errhint("Must be superuser or the user that prepared the transaction.")));
594 
595  /*
596  * Note: it probably would be possible to allow committing from
597  * another database; but at the moment NOTIFY is known not to work and
598  * there may be some other issues as well. Hence disallow until
599  * someone gets motivated to make it work.
600  */
601  if (MyDatabaseId != proc->databaseId)
602  ereport(ERROR,
603  (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
604  errmsg("prepared transaction belongs to another database"),
605  errhint("Connect to the database where the transaction was prepared to finish it.")));
606 
607  /* OK for me to lock it */
608  gxact->locking_backend = MyBackendId;
609  MyLockedGxact = gxact;
610 
611  LWLockRelease(TwoPhaseStateLock);
612 
613  return gxact;
614  }
615 
616  LWLockRelease(TwoPhaseStateLock);
617 
618  ereport(ERROR,
619  (errcode(ERRCODE_UNDEFINED_OBJECT),
620  errmsg("prepared transaction with identifier \"%s\" does not exist",
621  gid)));
622 
623  /* NOTREACHED */
624  return NULL;
625 }
626 
627 /*
628  * RemoveGXact
629  * Remove the prepared transaction from the shared memory array.
630  *
631  * NB: caller should have already removed it from ProcArray
632  */
633 static void
635 {
636  int i;
637 
638  Assert(LWLockHeldByMeInMode(TwoPhaseStateLock, LW_EXCLUSIVE));
639 
640  for (i = 0; i < TwoPhaseState->numPrepXacts; i++)
641  {
642  if (gxact == TwoPhaseState->prepXacts[i])
643  {
644  /* remove from the active array */
645  TwoPhaseState->numPrepXacts--;
646  TwoPhaseState->prepXacts[i] = TwoPhaseState->prepXacts[TwoPhaseState->numPrepXacts];
647 
648  /* and put it back in the freelist */
649  gxact->next = TwoPhaseState->freeGXacts;
650  TwoPhaseState->freeGXacts = gxact;
651 
652  return;
653  }
654  }
655 
656  elog(ERROR, "failed to find %p in GlobalTransaction array", gxact);
657 }
658 
659 /*
660  * Returns an array of all prepared transactions for the user-level
661  * function pg_prepared_xact.
662  *
663  * The returned array and all its elements are copies of internal data
664  * structures, to minimize the time we need to hold the TwoPhaseStateLock.
665  *
666  * WARNING -- we return even those transactions that are not fully prepared
667  * yet. The caller should filter them out if he doesn't want them.
668  *
669  * The returned array is palloc'd.
670  */
671 static int
673 {
674  GlobalTransaction array;
675  int num;
676  int i;
677 
678  LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
679 
680  if (TwoPhaseState->numPrepXacts == 0)
681  {
682  LWLockRelease(TwoPhaseStateLock);
683 
684  *gxacts = NULL;
685  return 0;
686  }
687 
688  num = TwoPhaseState->numPrepXacts;
689  array = (GlobalTransaction) palloc(sizeof(GlobalTransactionData) * num);
690  *gxacts = array;
691  for (i = 0; i < num; i++)
692  memcpy(array + i, TwoPhaseState->prepXacts[i],
693  sizeof(GlobalTransactionData));
694 
695  LWLockRelease(TwoPhaseStateLock);
696 
697  return num;
698 }
699 
700 
701 /* Working status for pg_prepared_xact */
702 typedef struct
703 {
705  int ngxacts;
706  int currIdx;
707 } Working_State;
708 
709 /*
710  * pg_prepared_xact
711  * Produce a view with one row per prepared transaction.
712  *
713  * This function is here so we don't have to export the
714  * GlobalTransactionData struct definition.
715  */
716 Datum
718 {
719  FuncCallContext *funcctx;
721 
722  if (SRF_IS_FIRSTCALL())
723  {
724  TupleDesc tupdesc;
725  MemoryContext oldcontext;
726 
727  /* create a function context for cross-call persistence */
728  funcctx = SRF_FIRSTCALL_INIT();
729 
730  /*
731  * Switch to memory context appropriate for multiple function calls
732  */
733  oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);
734 
735  /* build tupdesc for result tuples */
736  /* this had better match pg_prepared_xacts view in system_views.sql */
737  tupdesc = CreateTemplateTupleDesc(5);
738  TupleDescInitEntry(tupdesc, (AttrNumber) 1, "transaction",
739  XIDOID, -1, 0);
740  TupleDescInitEntry(tupdesc, (AttrNumber) 2, "gid",
741  TEXTOID, -1, 0);
742  TupleDescInitEntry(tupdesc, (AttrNumber) 3, "prepared",
743  TIMESTAMPTZOID, -1, 0);
744  TupleDescInitEntry(tupdesc, (AttrNumber) 4, "ownerid",
745  OIDOID, -1, 0);
746  TupleDescInitEntry(tupdesc, (AttrNumber) 5, "dbid",
747  OIDOID, -1, 0);
748 
749  funcctx->tuple_desc = BlessTupleDesc(tupdesc);
750 
751  /*
752  * Collect all the 2PC status information that we will format and send
753  * out as a result set.
754  */
755  status = (Working_State *) palloc(sizeof(Working_State));
756  funcctx->user_fctx = (void *) status;
757 
758  status->ngxacts = GetPreparedTransactionList(&status->array);
759  status->currIdx = 0;
760 
761  MemoryContextSwitchTo(oldcontext);
762  }
763 
764  funcctx = SRF_PERCALL_SETUP();
765  status = (Working_State *) funcctx->user_fctx;
766 
767  while (status->array != NULL && status->currIdx < status->ngxacts)
768  {
769  GlobalTransaction gxact = &status->array[status->currIdx++];
770  PGPROC *proc = &ProcGlobal->allProcs[gxact->pgprocno];
771  PGXACT *pgxact = &ProcGlobal->allPgXact[gxact->pgprocno];
772  Datum values[5];
773  bool nulls[5];
774  HeapTuple tuple;
775  Datum result;
776 
777  if (!gxact->valid)
778  continue;
779 
780  /*
781  * Form tuple with appropriate data.
782  */
783  MemSet(values, 0, sizeof(values));
784  MemSet(nulls, 0, sizeof(nulls));
785 
786  values[0] = TransactionIdGetDatum(pgxact->xid);
787  values[1] = CStringGetTextDatum(gxact->gid);
788  values[2] = TimestampTzGetDatum(gxact->prepared_at);
789  values[3] = ObjectIdGetDatum(gxact->owner);
790  values[4] = ObjectIdGetDatum(proc->databaseId);
791 
792  tuple = heap_form_tuple(funcctx->tuple_desc, values, nulls);
793  result = HeapTupleGetDatum(tuple);
794  SRF_RETURN_NEXT(funcctx, result);
795  }
796 
797  SRF_RETURN_DONE(funcctx);
798 }
799 
800 /*
801  * TwoPhaseGetGXact
802  * Get the GlobalTransaction struct for a prepared transaction
803  * specified by XID
804  *
805  * If lock_held is set to true, TwoPhaseStateLock will not be taken, so the
806  * caller had better hold it.
807  */
808 static GlobalTransaction
810 {
811  GlobalTransaction result = NULL;
812  int i;
813 
814  static TransactionId cached_xid = InvalidTransactionId;
815  static GlobalTransaction cached_gxact = NULL;
816 
817  Assert(!lock_held || LWLockHeldByMe(TwoPhaseStateLock));
818 
819  /*
820  * During a recovery, COMMIT PREPARED, or ABORT PREPARED, we'll be called
821  * repeatedly for the same XID. We can save work with a simple cache.
822  */
823  if (xid == cached_xid)
824  return cached_gxact;
825 
826  if (!lock_held)
827  LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
828 
829  for (i = 0; i < TwoPhaseState->numPrepXacts; i++)
830  {
831  GlobalTransaction gxact = TwoPhaseState->prepXacts[i];
832  PGXACT *pgxact = &ProcGlobal->allPgXact[gxact->pgprocno];
833 
834  if (pgxact->xid == xid)
835  {
836  result = gxact;
837  break;
838  }
839  }
840 
841  if (!lock_held)
842  LWLockRelease(TwoPhaseStateLock);
843 
844  if (result == NULL) /* should not happen */
845  elog(ERROR, "failed to find GlobalTransaction for xid %u", xid);
846 
847  cached_xid = xid;
848  cached_gxact = result;
849 
850  return result;
851 }
852 
853 /*
854  * TwoPhaseGetDummyBackendId
855  * Get the dummy backend ID for prepared transaction specified by XID
856  *
857  * Dummy backend IDs are similar to real backend IDs of real backends.
858  * They start at MaxBackends + 1, and are unique across all currently active
859  * real backends and prepared transactions. If lock_held is set to true,
860  * TwoPhaseStateLock will not be taken, so the caller had better hold it.
861  */
862 BackendId
864 {
865  GlobalTransaction gxact = TwoPhaseGetGXact(xid, lock_held);
866 
867  return gxact->dummyBackendId;
868 }
869 
870 /*
871  * TwoPhaseGetDummyProc
872  * Get the PGPROC that represents a prepared transaction specified by XID
873  *
874  * If lock_held is set to true, TwoPhaseStateLock will not be taken, so the
875  * caller had better hold it.
876  */
877 PGPROC *
879 {
880  GlobalTransaction gxact = TwoPhaseGetGXact(xid, lock_held);
881 
882  return &ProcGlobal->allProcs[gxact->pgprocno];
883 }
884 
885 /************************************************************************/
886 /* State file support */
887 /************************************************************************/
888 
889 #define TwoPhaseFilePath(path, xid) \
890  snprintf(path, MAXPGPATH, TWOPHASE_DIR "/%08X", xid)
891 
892 /*
893  * 2PC state file format:
894  *
895  * 1. TwoPhaseFileHeader
896  * 2. TransactionId[] (subtransactions)
897  * 3. RelFileNode[] (files to be deleted at commit)
898  * 4. RelFileNode[] (files to be deleted at abort)
899  * 5. SharedInvalidationMessage[] (inval messages to be sent at commit)
900  * 6. TwoPhaseRecordOnDisk
901  * 7. ...
902  * 8. TwoPhaseRecordOnDisk (end sentinel, rmid == TWOPHASE_RM_END_ID)
903  * 9. checksum (CRC-32C)
904  *
905  * Each segment except the final checksum is MAXALIGN'd.
906  */
907 
908 /*
909  * Header for a 2PC state file
910  */
911 #define TWOPHASE_MAGIC 0x57F94534 /* format identifier */
912 
914 
915 /*
916  * Header for each record in a state file
917  *
918  * NOTE: len counts only the rmgr data, not the TwoPhaseRecordOnDisk header.
919  * The rmgr data will be stored starting on a MAXALIGN boundary.
920  */
921 typedef struct TwoPhaseRecordOnDisk
922 {
923  uint32 len; /* length of rmgr data */
924  TwoPhaseRmgrId rmid; /* resource manager for this record */
925  uint16 info; /* flag bits for use by rmgr */
927 
928 /*
929  * During prepare, the state file is assembled in memory before writing it
930  * to WAL and the actual state file. We use a chain of StateFileChunk blocks
931  * for that.
932  */
933 typedef struct StateFileChunk
934 {
935  char *data;
939 
940 static struct xllist
941 {
942  StateFileChunk *head; /* first data block in the chain */
943  StateFileChunk *tail; /* last block in chain */
945  uint32 bytes_free; /* free bytes left in tail block */
946  uint32 total_len; /* total data bytes in chain */
947 } records;
948 
949 
950 /*
951  * Append a block of data to records data structure.
952  *
953  * NB: each block is padded to a MAXALIGN multiple. This must be
954  * accounted for when the file is later read!
955  *
956  * The data is copied, so the caller is free to modify it afterwards.
957  */
958 static void
959 save_state_data(const void *data, uint32 len)
960 {
961  uint32 padlen = MAXALIGN(len);
962 
963  if (padlen > records.bytes_free)
964  {
965  records.tail->next = palloc0(sizeof(StateFileChunk));
967  records.tail->len = 0;
968  records.tail->next = NULL;
970 
971  records.bytes_free = Max(padlen, 512);
973  }
974 
975  memcpy(((char *) records.tail->data) + records.tail->len, data, len);
976  records.tail->len += padlen;
977  records.bytes_free -= padlen;
978  records.total_len += padlen;
979 }
980 
981 /*
982  * Start preparing a state file.
983  *
984  * Initializes data structure and inserts the 2PC file header record.
985  */
986 void
988 {
989  PGPROC *proc = &ProcGlobal->allProcs[gxact->pgprocno];
990  PGXACT *pgxact = &ProcGlobal->allPgXact[gxact->pgprocno];
991  TransactionId xid = pgxact->xid;
992  TwoPhaseFileHeader hdr;
993  TransactionId *children;
994  RelFileNode *commitrels;
995  RelFileNode *abortrels;
996  SharedInvalidationMessage *invalmsgs;
997 
998  /* Initialize linked list */
999  records.head = palloc0(sizeof(StateFileChunk));
1000  records.head->len = 0;
1001  records.head->next = NULL;
1002 
1003  records.bytes_free = Max(sizeof(TwoPhaseFileHeader), 512);
1005 
1007  records.num_chunks = 1;
1008 
1009  records.total_len = 0;
1010 
1011  /* Create header */
1012  hdr.magic = TWOPHASE_MAGIC;
1013  hdr.total_len = 0; /* EndPrepare will fill this in */
1014  hdr.xid = xid;
1015  hdr.database = proc->databaseId;
1016  hdr.prepared_at = gxact->prepared_at;
1017  hdr.owner = gxact->owner;
1018  hdr.nsubxacts = xactGetCommittedChildren(&children);
1019  hdr.ncommitrels = smgrGetPendingDeletes(true, &commitrels);
1020  hdr.nabortrels = smgrGetPendingDeletes(false, &abortrels);
1022  &hdr.initfileinval);
1023  hdr.gidlen = strlen(gxact->gid) + 1; /* Include '\0' */
1024 
1025  save_state_data(&hdr, sizeof(TwoPhaseFileHeader));
1026  save_state_data(gxact->gid, hdr.gidlen);
1027 
1028  /*
1029  * Add the additional info about subxacts, deletable files and cache
1030  * invalidation messages.
1031  */
1032  if (hdr.nsubxacts > 0)
1033  {
1034  save_state_data(children, hdr.nsubxacts * sizeof(TransactionId));
1035  /* While we have the child-xact data, stuff it in the gxact too */
1036  GXactLoadSubxactData(gxact, hdr.nsubxacts, children);
1037  }
1038  if (hdr.ncommitrels > 0)
1039  {
1040  save_state_data(commitrels, hdr.ncommitrels * sizeof(RelFileNode));
1041  pfree(commitrels);
1042  }
1043  if (hdr.nabortrels > 0)
1044  {
1045  save_state_data(abortrels, hdr.nabortrels * sizeof(RelFileNode));
1046  pfree(abortrels);
1047  }
1048  if (hdr.ninvalmsgs > 0)
1049  {
1050  save_state_data(invalmsgs,
1051  hdr.ninvalmsgs * sizeof(SharedInvalidationMessage));
1052  pfree(invalmsgs);
1053  }
1054 }
1055 
1056 /*
1057  * Finish preparing state data and writing it to WAL.
1058  */
1059 void
1061 {
1062  TwoPhaseFileHeader *hdr;
1063  StateFileChunk *record;
1064  bool replorigin;
1065 
1066  /* Add the end sentinel to the list of 2PC records */
1068  NULL, 0);
1069 
1070  /* Go back and fill in total_len in the file header record */
1071  hdr = (TwoPhaseFileHeader *) records.head->data;
1072  Assert(hdr->magic == TWOPHASE_MAGIC);
1073  hdr->total_len = records.total_len + sizeof(pg_crc32c);
1074 
1075  replorigin = (replorigin_session_origin != InvalidRepOriginId &&
1077 
1078  if (replorigin)
1079  {
1083  }
1084  else
1085  {
1087  hdr->origin_timestamp = 0;
1088  }
1089 
1090  /*
1091  * If the data size exceeds MaxAllocSize, we won't be able to read it in
1092  * ReadTwoPhaseFile. Check for that now, rather than fail in the case
1093  * where we write data to file and then re-read at commit time.
1094  */
1095  if (hdr->total_len > MaxAllocSize)
1096  ereport(ERROR,
1097  (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
1098  errmsg("two-phase state file maximum length exceeded")));
1099 
1100  /*
1101  * Now writing 2PC state data to WAL. We let the WAL's CRC protection
1102  * cover us, so no need to calculate a separate CRC.
1103  *
1104  * We have to set delayChkpt here, too; otherwise a checkpoint starting
1105  * immediately after the WAL record is inserted could complete without
1106  * fsync'ing our state file. (This is essentially the same kind of race
1107  * condition as the COMMIT-to-clog-write case that RecordTransactionCommit
1108  * uses delayChkpt for; see notes there.)
1109  *
1110  * We save the PREPARE record's location in the gxact for later use by
1111  * CheckPointTwoPhase.
1112  */
1114 
1116 
1117  MyPgXact->delayChkpt = true;
1118 
1119  XLogBeginInsert();
1120  for (record = records.head; record != NULL; record = record->next)
1121  XLogRegisterData(record->data, record->len);
1122 
1124 
1125  gxact->prepare_end_lsn = XLogInsert(RM_XACT_ID, XLOG_XACT_PREPARE);
1126 
1127  if (replorigin)
1128  {
1129  /* Move LSNs forward for this replication origin */
1131  gxact->prepare_end_lsn);
1132  }
1133 
1134  XLogFlush(gxact->prepare_end_lsn);
1135 
1136  /* If we crash now, we have prepared: WAL replay will fix things */
1137 
1138  /* Store record's start location to read that later on Commit */
1140 
1141  /*
1142  * Mark the prepared transaction as valid. As soon as xact.c marks
1143  * MyPgXact as not running our XID (which it will do immediately after
1144  * this function returns), others can commit/rollback the xact.
1145  *
1146  * NB: a side effect of this is to make a dummy ProcArray entry for the
1147  * prepared XID. This must happen before we clear the XID from MyPgXact,
1148  * else there is a window where the XID is not running according to
1149  * TransactionIdIsInProgress, and onlookers would be entitled to assume
1150  * the xact crashed. Instead we have a window where the same XID appears
1151  * twice in ProcArray, which is OK.
1152  */
1153  MarkAsPrepared(gxact, false);
1154 
1155  /*
1156  * Now we can mark ourselves as out of the commit critical section: a
1157  * checkpoint starting after this will certainly see the gxact as a
1158  * candidate for fsyncing.
1159  */
1160  MyPgXact->delayChkpt = false;
1161 
1162  /*
1163  * Remember that we have this GlobalTransaction entry locked for us. If
1164  * we crash after this point, it's too late to abort, but we must unlock
1165  * it so that the prepared transaction can be committed or rolled back.
1166  */
1167  MyLockedGxact = gxact;
1168 
1169  END_CRIT_SECTION();
1170 
1171  /*
1172  * Wait for synchronous replication, if required.
1173  *
1174  * Note that at this stage we have marked the prepare, but still show as
1175  * running in the procarray (twice!) and continue to hold locks.
1176  */
1177  SyncRepWaitForLSN(gxact->prepare_end_lsn, false);
1178 
1179  records.tail = records.head = NULL;
1180  records.num_chunks = 0;
1181 }
1182 
1183 /*
1184  * Register a 2PC record to be written to state file.
1185  */
1186 void
1188  const void *data, uint32 len)
1189 {
1190  TwoPhaseRecordOnDisk record;
1191 
1192  record.rmid = rmid;
1193  record.info = info;
1194  record.len = len;
1195  save_state_data(&record, sizeof(TwoPhaseRecordOnDisk));
1196  if (len > 0)
1197  save_state_data(data, len);
1198 }
1199 
1200 
1201 /*
1202  * Read and validate the state file for xid.
1203  *
1204  * If it looks OK (has a valid magic number and CRC), return the palloc'd
1205  * contents of the file, issuing an error when finding corrupted data. If
1206  * missing_ok is true, which indicates that missing files can be safely
1207  * ignored, then return NULL. This state can be reached when doing recovery.
1208  */
1209 static char *
1211 {
1212  char path[MAXPGPATH];
1213  char *buf;
1214  TwoPhaseFileHeader *hdr;
1215  int fd;
1216  struct stat stat;
1217  uint32 crc_offset;
1218  pg_crc32c calc_crc,
1219  file_crc;
1220  int r;
1221 
1222  TwoPhaseFilePath(path, xid);
1223 
1224  fd = OpenTransientFile(path, O_RDONLY | PG_BINARY);
1225  if (fd < 0)
1226  {
1227  if (missing_ok && errno == ENOENT)
1228  return NULL;
1229 
1230  ereport(ERROR,
1232  errmsg("could not open file \"%s\": %m", path)));
1233  }
1234 
1235  /*
1236  * Check file length. We can determine a lower bound pretty easily. We
1237  * set an upper bound to avoid palloc() failure on a corrupt file, though
1238  * we can't guarantee that we won't get an out of memory error anyway,
1239  * even on a valid file.
1240  */
1241  if (fstat(fd, &stat))
1242  ereport(ERROR,
1244  errmsg("could not stat file \"%s\": %m", path)));
1245 
1246  if (stat.st_size < (MAXALIGN(sizeof(TwoPhaseFileHeader)) +
1247  MAXALIGN(sizeof(TwoPhaseRecordOnDisk)) +
1248  sizeof(pg_crc32c)) ||
1249  stat.st_size > MaxAllocSize)
1250  ereport(ERROR,
1252  errmsg_plural("incorrect size of file \"%s\": %zu byte",
1253  "incorrect size of file \"%s\": %zu bytes",
1254  (Size) stat.st_size, path,
1255  (Size) stat.st_size)));
1256 
1257  crc_offset = stat.st_size - sizeof(pg_crc32c);
1258  if (crc_offset != MAXALIGN(crc_offset))
1259  ereport(ERROR,
1261  errmsg("incorrect alignment of CRC offset for file \"%s\"",
1262  path)));
1263 
1264  /*
1265  * OK, slurp in the file.
1266  */
1267  buf = (char *) palloc(stat.st_size);
1268 
1270  r = read(fd, buf, stat.st_size);
1271  if (r != stat.st_size)
1272  {
1273  if (r < 0)
1274  ereport(ERROR,
1276  errmsg("could not read file \"%s\": %m", path)));
1277  else
1278  ereport(ERROR,
1279  (errmsg("could not read file \"%s\": read %d of %zu",
1280  path, r, (Size) stat.st_size)));
1281  }
1282 
1284 
1285  if (CloseTransientFile(fd) != 0)
1286  ereport(ERROR,
1288  errmsg("could not close file \"%s\": %m", path)));
1289 
1290  hdr = (TwoPhaseFileHeader *) buf;
1291  if (hdr->magic != TWOPHASE_MAGIC)
1292  ereport(ERROR,
1294  errmsg("invalid magic number stored in file \"%s\"",
1295  path)));
1296 
1297  if (hdr->total_len != stat.st_size)
1298  ereport(ERROR,
1300  errmsg("invalid size stored in file \"%s\"",
1301  path)));
1302 
1303  INIT_CRC32C(calc_crc);
1304  COMP_CRC32C(calc_crc, buf, crc_offset);
1305  FIN_CRC32C(calc_crc);
1306 
1307  file_crc = *((pg_crc32c *) (buf + crc_offset));
1308 
1309  if (!EQ_CRC32C(calc_crc, file_crc))
1310  ereport(ERROR,
1312  errmsg("calculated CRC checksum does not match value stored in file \"%s\"",
1313  path)));
1314 
1315  return buf;
1316 }
1317 
1318 
1319 /*
1320  * Reads 2PC data from xlog. During checkpoint this data will be moved to
1321  * twophase files and ReadTwoPhaseFile should be used instead.
1322  *
1323  * Note clearly that this function can access WAL during normal operation,
1324  * similarly to the way WALSender or Logical Decoding would do.
1325  */
1326 static void
1327 XlogReadTwoPhaseData(XLogRecPtr lsn, char **buf, int *len)
1328 {
1329  XLogRecord *record;
1330  XLogReaderState *xlogreader;
1331  char *errormsg;
1332 
1333  xlogreader = XLogReaderAllocate(wal_segment_size, NULL,
1334  &read_local_xlog_page, NULL);
1335  if (!xlogreader)
1336  ereport(ERROR,
1337  (errcode(ERRCODE_OUT_OF_MEMORY),
1338  errmsg("out of memory"),
1339  errdetail("Failed while allocating a WAL reading processor.")));
1340 
1341  record = XLogReadRecord(xlogreader, lsn, &errormsg);
1342  if (record == NULL)
1343  ereport(ERROR,
1345  errmsg("could not read two-phase state from WAL at %X/%X",
1346  (uint32) (lsn >> 32),
1347  (uint32) lsn)));
1348 
1349  if (XLogRecGetRmid(xlogreader) != RM_XACT_ID ||
1351  ereport(ERROR,
1353  errmsg("expected two-phase state data is not present in WAL at %X/%X",
1354  (uint32) (lsn >> 32),
1355  (uint32) lsn)));
1356 
1357  if (len != NULL)
1358  *len = XLogRecGetDataLen(xlogreader);
1359 
1360  *buf = palloc(sizeof(char) * XLogRecGetDataLen(xlogreader));
1361  memcpy(*buf, XLogRecGetData(xlogreader), sizeof(char) * XLogRecGetDataLen(xlogreader));
1362 
1363  XLogReaderFree(xlogreader);
1364 }
1365 
1366 
1367 /*
1368  * Confirms an xid is prepared, during recovery
1369  */
1370 bool
1372 {
1373  char *buf;
1374  TwoPhaseFileHeader *hdr;
1375  bool result;
1376 
1378 
1379  if (max_prepared_xacts <= 0)
1380  return false; /* nothing to do */
1381 
1382  /* Read and validate file */
1383  buf = ReadTwoPhaseFile(xid, true);
1384  if (buf == NULL)
1385  return false;
1386 
1387  /* Check header also */
1388  hdr = (TwoPhaseFileHeader *) buf;
1389  result = TransactionIdEquals(hdr->xid, xid);
1390  pfree(buf);
1391 
1392  return result;
1393 }
1394 
1395 /*
1396  * FinishPreparedTransaction: execute COMMIT PREPARED or ROLLBACK PREPARED
1397  */
1398 void
1399 FinishPreparedTransaction(const char *gid, bool isCommit)
1400 {
1401  GlobalTransaction gxact;
1402  PGPROC *proc;
1403  PGXACT *pgxact;
1405  char *buf;
1406  char *bufptr;
1407  TwoPhaseFileHeader *hdr;
1408  TransactionId latestXid;
1409  TransactionId *children;
1410  RelFileNode *commitrels;
1411  RelFileNode *abortrels;
1412  RelFileNode *delrels;
1413  int ndelrels;
1414  SharedInvalidationMessage *invalmsgs;
1415 
1416  /*
1417  * Validate the GID, and lock the GXACT to ensure that two backends do not
1418  * try to commit the same GID at once.
1419  */
1420  gxact = LockGXact(gid, GetUserId());
1421  proc = &ProcGlobal->allProcs[gxact->pgprocno];
1422  pgxact = &ProcGlobal->allPgXact[gxact->pgprocno];
1423  xid = pgxact->xid;
1424 
1425  /*
1426  * Read and validate 2PC state data. State data will typically be stored
1427  * in WAL files if the LSN is after the last checkpoint record, or moved
1428  * to disk if for some reason they have lived for a long time.
1429  */
1430  if (gxact->ondisk)
1431  buf = ReadTwoPhaseFile(xid, false);
1432  else
1433  XlogReadTwoPhaseData(gxact->prepare_start_lsn, &buf, NULL);
1434 
1435 
1436  /*
1437  * Disassemble the header area
1438  */
1439  hdr = (TwoPhaseFileHeader *) buf;
1440  Assert(TransactionIdEquals(hdr->xid, xid));
1441  bufptr = buf + MAXALIGN(sizeof(TwoPhaseFileHeader));
1442  bufptr += MAXALIGN(hdr->gidlen);
1443  children = (TransactionId *) bufptr;
1444  bufptr += MAXALIGN(hdr->nsubxacts * sizeof(TransactionId));
1445  commitrels = (RelFileNode *) bufptr;
1446  bufptr += MAXALIGN(hdr->ncommitrels * sizeof(RelFileNode));
1447  abortrels = (RelFileNode *) bufptr;
1448  bufptr += MAXALIGN(hdr->nabortrels * sizeof(RelFileNode));
1449  invalmsgs = (SharedInvalidationMessage *) bufptr;
1450  bufptr += MAXALIGN(hdr->ninvalmsgs * sizeof(SharedInvalidationMessage));
1451 
1452  /* compute latestXid among all children */
1453  latestXid = TransactionIdLatest(xid, hdr->nsubxacts, children);
1454 
1455  /* Prevent cancel/die interrupt while cleaning up */
1456  HOLD_INTERRUPTS();
1457 
1458  /*
1459  * The order of operations here is critical: make the XLOG entry for
1460  * commit or abort, then mark the transaction committed or aborted in
1461  * pg_xact, then remove its PGPROC from the global ProcArray (which means
1462  * TransactionIdIsInProgress will stop saying the prepared xact is in
1463  * progress), then run the post-commit or post-abort callbacks. The
1464  * callbacks will release the locks the transaction held.
1465  */
1466  if (isCommit)
1468  hdr->nsubxacts, children,
1469  hdr->ncommitrels, commitrels,
1470  hdr->ninvalmsgs, invalmsgs,
1471  hdr->initfileinval, gid);
1472  else
1474  hdr->nsubxacts, children,
1475  hdr->nabortrels, abortrels,
1476  gid);
1477 
1478  ProcArrayRemove(proc, latestXid);
1479 
1480  /*
1481  * In case we fail while running the callbacks, mark the gxact invalid so
1482  * no one else will try to commit/rollback, and so it will be recycled if
1483  * we fail after this point. It is still locked by our backend so it
1484  * won't go away yet.
1485  *
1486  * (We assume it's safe to do this without taking TwoPhaseStateLock.)
1487  */
1488  gxact->valid = false;
1489 
1490  /*
1491  * We have to remove any files that were supposed to be dropped. For
1492  * consistency with the regular xact.c code paths, must do this before
1493  * releasing locks, so do it before running the callbacks.
1494  *
1495  * NB: this code knows that we couldn't be dropping any temp rels ...
1496  */
1497  if (isCommit)
1498  {
1499  delrels = commitrels;
1500  ndelrels = hdr->ncommitrels;
1501  }
1502  else
1503  {
1504  delrels = abortrels;
1505  ndelrels = hdr->nabortrels;
1506  }
1507 
1508  /* Make sure files supposed to be dropped are dropped */
1509  DropRelationFiles(delrels, ndelrels, false);
1510 
1511  /*
1512  * Handle cache invalidation messages.
1513  *
1514  * Relcache init file invalidation requires processing both before and
1515  * after we send the SI messages. See AtEOXact_Inval()
1516  */
1517  if (hdr->initfileinval)
1519  SendSharedInvalidMessages(invalmsgs, hdr->ninvalmsgs);
1520  if (hdr->initfileinval)
1522 
1523  /*
1524  * Acquire the two-phase lock. We want to work on the two-phase callbacks
1525  * while holding it to avoid potential conflicts with other transactions
1526  * attempting to use the same GID, so the lock is released once the shared
1527  * memory state is cleared.
1528  */
1529  LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
1530 
1531  /* And now do the callbacks */
1532  if (isCommit)
1534  else
1536 
1537  PredicateLockTwoPhaseFinish(xid, isCommit);
1538 
1539  /* Clear shared memory state */
1540  RemoveGXact(gxact);
1541 
1542  /*
1543  * Release the lock as all callbacks are called and shared memory cleanup
1544  * is done.
1545  */
1546  LWLockRelease(TwoPhaseStateLock);
1547 
1548  /* Count the prepared xact as committed or aborted */
1549  AtEOXact_PgStat(isCommit, false);
1550 
1551  /*
1552  * And now we can clean up any files we may have left.
1553  */
1554  if (gxact->ondisk)
1555  RemoveTwoPhaseFile(xid, true);
1556 
1557  MyLockedGxact = NULL;
1558 
1560 
1561  pfree(buf);
1562 }
1563 
1564 /*
1565  * Scan 2PC state data in memory and call the indicated callbacks for each 2PC record.
1566  */
1567 static void
1569  const TwoPhaseCallback callbacks[])
1570 {
1571  for (;;)
1572  {
1573  TwoPhaseRecordOnDisk *record = (TwoPhaseRecordOnDisk *) bufptr;
1574 
1575  Assert(record->rmid <= TWOPHASE_RM_MAX_ID);
1576  if (record->rmid == TWOPHASE_RM_END_ID)
1577  break;
1578 
1579  bufptr += MAXALIGN(sizeof(TwoPhaseRecordOnDisk));
1580 
1581  if (callbacks[record->rmid] != NULL)
1582  callbacks[record->rmid] (xid, record->info,
1583  (void *) bufptr, record->len);
1584 
1585  bufptr += MAXALIGN(record->len);
1586  }
1587 }
1588 
1589 /*
1590  * Remove the 2PC file for the specified XID.
1591  *
1592  * If giveWarning is false, do not complain about file-not-present;
1593  * this is an expected case during WAL replay.
1594  */
1595 static void
1597 {
1598  char path[MAXPGPATH];
1599 
1600  TwoPhaseFilePath(path, xid);
1601  if (unlink(path))
1602  if (errno != ENOENT || giveWarning)
1603  ereport(WARNING,
1605  errmsg("could not remove file \"%s\": %m", path)));
1606 }
1607 
1608 /*
1609  * Recreates a state file. This is used in WAL replay and during
1610  * checkpoint creation.
1611  *
1612  * Note: content and len don't include CRC.
1613  */
1614 static void
1615 RecreateTwoPhaseFile(TransactionId xid, void *content, int len)
1616 {
1617  char path[MAXPGPATH];
1618  pg_crc32c statefile_crc;
1619  int fd;
1620 
1621  /* Recompute CRC */
1622  INIT_CRC32C(statefile_crc);
1623  COMP_CRC32C(statefile_crc, content, len);
1624  FIN_CRC32C(statefile_crc);
1625 
1626  TwoPhaseFilePath(path, xid);
1627 
1628  fd = OpenTransientFile(path,
1629  O_CREAT | O_TRUNC | O_WRONLY | PG_BINARY);
1630  if (fd < 0)
1631  ereport(ERROR,
1633  errmsg("could not recreate file \"%s\": %m", path)));
1634 
1635  /* Write content and CRC */
1636  errno = 0;
1638  if (write(fd, content, len) != len)
1639  {
1640  /* if write didn't set errno, assume problem is no disk space */
1641  if (errno == 0)
1642  errno = ENOSPC;
1643  ereport(ERROR,
1645  errmsg("could not write file \"%s\": %m", path)));
1646  }
1647  if (write(fd, &statefile_crc, sizeof(pg_crc32c)) != sizeof(pg_crc32c))
1648  {
1649  /* if write didn't set errno, assume problem is no disk space */
1650  if (errno == 0)
1651  errno = ENOSPC;
1652  ereport(ERROR,
1654  errmsg("could not write file \"%s\": %m", path)));
1655  }
1657 
1658  /*
1659  * We must fsync the file because the end-of-replay checkpoint will not do
1660  * so, there being no GXACT in shared memory yet to tell it to.
1661  */
1663  if (pg_fsync(fd) != 0)
1664  ereport(ERROR,
1666  errmsg("could not fsync file \"%s\": %m", path)));
1668 
1669  if (CloseTransientFile(fd) != 0)
1670  ereport(ERROR,
1672  errmsg("could not close file \"%s\": %m", path)));
1673 }
1674 
1675 /*
1676  * CheckPointTwoPhase -- handle 2PC component of checkpointing.
1677  *
1678  * We must fsync the state file of any GXACT that is valid or has been
1679  * generated during redo and has a PREPARE LSN <= the checkpoint's redo
1680  * horizon. (If the gxact isn't valid yet, has not been generated in
1681  * redo, or has a later LSN, this checkpoint is not responsible for
1682  * fsyncing it.)
1683  *
1684  * This is deliberately run as late as possible in the checkpoint sequence,
1685  * because GXACTs ordinarily have short lifespans, and so it is quite
1686  * possible that GXACTs that were valid at checkpoint start will no longer
1687  * exist if we wait a little bit. With typical checkpoint settings this
1688  * will be about 3 minutes for an online checkpoint, so as a result we
1689  * expect that there will be no GXACTs that need to be copied to disk.
1690  *
1691  * If a GXACT remains valid across multiple checkpoints, it will already
1692  * be on disk so we don't bother to repeat that write.
1693  */
1694 void
1696 {
1697  int i;
1698  int serialized_xacts = 0;
1699 
1700  if (max_prepared_xacts <= 0)
1701  return; /* nothing to do */
1702 
1703  TRACE_POSTGRESQL_TWOPHASE_CHECKPOINT_START();
1704 
1705  /*
1706  * We are expecting there to be zero GXACTs that need to be copied to
1707  * disk, so we perform all I/O while holding TwoPhaseStateLock for
1708  * simplicity. This prevents any new xacts from preparing while this
1709  * occurs, which shouldn't be a problem since the presence of long-lived
1710  * prepared xacts indicates the transaction manager isn't active.
1711  *
1712  * It's also possible to move I/O out of the lock, but on every error we
1713  * should check whether somebody committed our transaction in different
1714  * backend. Let's leave this optimization for future, if somebody will
1715  * spot that this place cause bottleneck.
1716  *
1717  * Note that it isn't possible for there to be a GXACT with a
1718  * prepare_end_lsn set prior to the last checkpoint yet is marked invalid,
1719  * because of the efforts with delayChkpt.
1720  */
1721  LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
1722  for (i = 0; i < TwoPhaseState->numPrepXacts; i++)
1723  {
1724  /*
1725  * Note that we are using gxact not pgxact so this works in recovery
1726  * also
1727  */
1728  GlobalTransaction gxact = TwoPhaseState->prepXacts[i];
1729 
1730  if ((gxact->valid || gxact->inredo) &&
1731  !gxact->ondisk &&
1732  gxact->prepare_end_lsn <= redo_horizon)
1733  {
1734  char *buf;
1735  int len;
1736 
1737  XlogReadTwoPhaseData(gxact->prepare_start_lsn, &buf, &len);
1738  RecreateTwoPhaseFile(gxact->xid, buf, len);
1739  gxact->ondisk = true;
1742  pfree(buf);
1743  serialized_xacts++;
1744  }
1745  }
1746  LWLockRelease(TwoPhaseStateLock);
1747 
1748  /*
1749  * Flush unconditionally the parent directory to make any information
1750  * durable on disk. Two-phase files could have been removed and those
1751  * removals need to be made persistent as well as any files newly created
1752  * previously since the last checkpoint.
1753  */
1754  fsync_fname(TWOPHASE_DIR, true);
1755 
1756  TRACE_POSTGRESQL_TWOPHASE_CHECKPOINT_DONE();
1757 
1758  if (log_checkpoints && serialized_xacts > 0)
1759  ereport(LOG,
1760  (errmsg_plural("%u two-phase state file was written "
1761  "for a long-running prepared transaction",
1762  "%u two-phase state files were written "
1763  "for long-running prepared transactions",
1764  serialized_xacts,
1765  serialized_xacts)));
1766 }
1767 
1768 /*
1769  * restoreTwoPhaseData
1770  *
1771  * Scan pg_twophase and fill TwoPhaseState depending on the on-disk data.
1772  * This is called once at the beginning of recovery, saving any extra
1773  * lookups in the future. Two-phase files that are newer than the
1774  * minimum XID horizon are discarded on the way.
1775  */
1776 void
1778 {
1779  DIR *cldir;
1780  struct dirent *clde;
1781 
1782  LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
1783  cldir = AllocateDir(TWOPHASE_DIR);
1784  while ((clde = ReadDir(cldir, TWOPHASE_DIR)) != NULL)
1785  {
1786  if (strlen(clde->d_name) == 8 &&
1787  strspn(clde->d_name, "0123456789ABCDEF") == 8)
1788  {
1790  char *buf;
1791 
1792  xid = (TransactionId) strtoul(clde->d_name, NULL, 16);
1793 
1795  true, false, false);
1796  if (buf == NULL)
1797  continue;
1798 
1801  }
1802  }
1803  LWLockRelease(TwoPhaseStateLock);
1804  FreeDir(cldir);
1805 }
1806 
1807 /*
1808  * PrescanPreparedTransactions
1809  *
1810  * Scan the shared memory entries of TwoPhaseState and determine the range
1811  * of valid XIDs present. This is run during database startup, after we
1812  * have completed reading WAL. ShmemVariableCache->nextFullXid has been set to
1813  * one more than the highest XID for which evidence exists in WAL.
1814  *
1815  * We throw away any prepared xacts with main XID beyond nextFullXid --- if any
1816  * are present, it suggests that the DBA has done a PITR recovery to an
1817  * earlier point in time without cleaning out pg_twophase. We dare not
1818  * try to recover such prepared xacts since they likely depend on database
1819  * state that doesn't exist now.
1820  *
1821  * However, we will advance nextFullXid beyond any subxact XIDs belonging to
1822  * valid prepared xacts. We need to do this since subxact commit doesn't
1823  * write a WAL entry, and so there might be no evidence in WAL of those
1824  * subxact XIDs.
1825  *
1826  * On corrupted two-phase files, fail immediately. Keeping around broken
1827  * entries and let replay continue causes harm on the system, and a new
1828  * backup should be rolled in.
1829  *
1830  * Our other responsibility is to determine and return the oldest valid XID
1831  * among the prepared xacts (if none, return ShmemVariableCache->nextFullXid).
1832  * This is needed to synchronize pg_subtrans startup properly.
1833  *
1834  * If xids_p and nxids_p are not NULL, pointer to a palloc'd array of all
1835  * top-level xids is stored in *xids_p. The number of entries in the array
1836  * is returned in *nxids_p.
1837  */
1840 {
1842  TransactionId origNextXid = XidFromFullTransactionId(nextFullXid);
1843  TransactionId result = origNextXid;
1844  TransactionId *xids = NULL;
1845  int nxids = 0;
1846  int allocsize = 0;
1847  int i;
1848 
1849  LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
1850  for (i = 0; i < TwoPhaseState->numPrepXacts; i++)
1851  {
1853  char *buf;
1854  GlobalTransaction gxact = TwoPhaseState->prepXacts[i];
1855 
1856  Assert(gxact->inredo);
1857 
1858  xid = gxact->xid;
1859 
1860  buf = ProcessTwoPhaseBuffer(xid,
1861  gxact->prepare_start_lsn,
1862  gxact->ondisk, false, true);
1863 
1864  if (buf == NULL)
1865  continue;
1866 
1867  /*
1868  * OK, we think this file is valid. Incorporate xid into the
1869  * running-minimum result.
1870  */
1871  if (TransactionIdPrecedes(xid, result))
1872  result = xid;
1873 
1874  if (xids_p)
1875  {
1876  if (nxids == allocsize)
1877  {
1878  if (nxids == 0)
1879  {
1880  allocsize = 10;
1881  xids = palloc(allocsize * sizeof(TransactionId));
1882  }
1883  else
1884  {
1885  allocsize = allocsize * 2;
1886  xids = repalloc(xids, allocsize * sizeof(TransactionId));
1887  }
1888  }
1889  xids[nxids++] = xid;
1890  }
1891 
1892  pfree(buf);
1893  }
1894  LWLockRelease(TwoPhaseStateLock);
1895 
1896  if (xids_p)
1897  {
1898  *xids_p = xids;
1899  *nxids_p = nxids;
1900  }
1901 
1902  return result;
1903 }
1904 
1905 /*
1906  * StandbyRecoverPreparedTransactions
1907  *
1908  * Scan the shared memory entries of TwoPhaseState and setup all the required
1909  * information to allow standby queries to treat prepared transactions as still
1910  * active.
1911  *
1912  * This is never called at the end of recovery - we use
1913  * RecoverPreparedTransactions() at that point.
1914  *
1915  * The lack of calls to SubTransSetParent() calls here is by design;
1916  * those calls are made by RecoverPreparedTransactions() at the end of recovery
1917  * for those xacts that need this.
1918  */
1919 void
1921 {
1922  int i;
1923 
1924  LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
1925  for (i = 0; i < TwoPhaseState->numPrepXacts; i++)
1926  {
1928  char *buf;
1929  GlobalTransaction gxact = TwoPhaseState->prepXacts[i];
1930 
1931  Assert(gxact->inredo);
1932 
1933  xid = gxact->xid;
1934 
1935  buf = ProcessTwoPhaseBuffer(xid,
1936  gxact->prepare_start_lsn,
1937  gxact->ondisk, false, false);
1938  if (buf != NULL)
1939  pfree(buf);
1940  }
1941  LWLockRelease(TwoPhaseStateLock);
1942 }
1943 
1944 /*
1945  * RecoverPreparedTransactions
1946  *
1947  * Scan the shared memory entries of TwoPhaseState and reload the state for
1948  * each prepared transaction (reacquire locks, etc).
1949  *
1950  * This is run at the end of recovery, but before we allow backends to write
1951  * WAL.
1952  *
1953  * At the end of recovery the way we take snapshots will change. We now need
1954  * to mark all running transactions with their full SubTransSetParent() info
1955  * to allow normal snapshots to work correctly if snapshots overflow.
1956  * We do this here because by definition prepared transactions are the only
1957  * type of write transaction still running, so this is necessary and
1958  * complete.
1959  */
1960 void
1962 {
1963  int i;
1964 
1965  LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
1966  for (i = 0; i < TwoPhaseState->numPrepXacts; i++)
1967  {
1969  char *buf;
1970  GlobalTransaction gxact = TwoPhaseState->prepXacts[i];
1971  char *bufptr;
1972  TwoPhaseFileHeader *hdr;
1973  TransactionId *subxids;
1974  const char *gid;
1975 
1976  xid = gxact->xid;
1977 
1978  /*
1979  * Reconstruct subtrans state for the transaction --- needed because
1980  * pg_subtrans is not preserved over a restart. Note that we are
1981  * linking all the subtransactions directly to the top-level XID;
1982  * there may originally have been a more complex hierarchy, but
1983  * there's no need to restore that exactly. It's possible that
1984  * SubTransSetParent has been set before, if the prepared transaction
1985  * generated xid assignment records.
1986  */
1987  buf = ProcessTwoPhaseBuffer(xid,
1988  gxact->prepare_start_lsn,
1989  gxact->ondisk, true, false);
1990  if (buf == NULL)
1991  continue;
1992 
1993  ereport(LOG,
1994  (errmsg("recovering prepared transaction %u from shared memory", xid)));
1995 
1996  hdr = (TwoPhaseFileHeader *) buf;
1997  Assert(TransactionIdEquals(hdr->xid, xid));
1998  bufptr = buf + MAXALIGN(sizeof(TwoPhaseFileHeader));
1999  gid = (const char *) bufptr;
2000  bufptr += MAXALIGN(hdr->gidlen);
2001  subxids = (TransactionId *) bufptr;
2002  bufptr += MAXALIGN(hdr->nsubxacts * sizeof(TransactionId));
2003  bufptr += MAXALIGN(hdr->ncommitrels * sizeof(RelFileNode));
2004  bufptr += MAXALIGN(hdr->nabortrels * sizeof(RelFileNode));
2005  bufptr += MAXALIGN(hdr->ninvalmsgs * sizeof(SharedInvalidationMessage));
2006 
2007  /*
2008  * Recreate its GXACT and dummy PGPROC. But, check whether it was
2009  * added in redo and already has a shmem entry for it.
2010  */
2011  MarkAsPreparingGuts(gxact, xid, gid,
2012  hdr->prepared_at,
2013  hdr->owner, hdr->database);
2014 
2015  /* recovered, so reset the flag for entries generated by redo */
2016  gxact->inredo = false;
2017 
2018  GXactLoadSubxactData(gxact, hdr->nsubxacts, subxids);
2019  MarkAsPrepared(gxact, true);
2020 
2021  LWLockRelease(TwoPhaseStateLock);
2022 
2023  /*
2024  * Recover other state (notably locks) using resource managers.
2025  */
2027 
2028  /*
2029  * Release locks held by the standby process after we process each
2030  * prepared transaction. As a result, we don't need too many
2031  * additional locks at any one time.
2032  */
2033  if (InHotStandby)
2034  StandbyReleaseLockTree(xid, hdr->nsubxacts, subxids);
2035 
2036  /*
2037  * We're done with recovering this transaction. Clear MyLockedGxact,
2038  * like we do in PrepareTransaction() during normal operation.
2039  */
2041 
2042  pfree(buf);
2043 
2044  LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE);
2045  }
2046 
2047  LWLockRelease(TwoPhaseStateLock);
2048 }
2049 
2050 /*
2051  * ProcessTwoPhaseBuffer
2052  *
2053  * Given a transaction id, read it either from disk or read it directly
2054  * via shmem xlog record pointer using the provided "prepare_start_lsn".
2055  *
2056  * If setParent is true, set up subtransaction parent linkages.
2057  *
2058  * If setNextXid is true, set ShmemVariableCache->nextFullXid to the newest
2059  * value scanned.
2060  */
2061 static char *
2064  bool fromdisk,
2065  bool setParent, bool setNextXid)
2066 {
2068  TransactionId origNextXid = XidFromFullTransactionId(nextFullXid);
2069  TransactionId *subxids;
2070  char *buf;
2071  TwoPhaseFileHeader *hdr;
2072  int i;
2073 
2074  Assert(LWLockHeldByMeInMode(TwoPhaseStateLock, LW_EXCLUSIVE));
2075 
2076  if (!fromdisk)
2077  Assert(prepare_start_lsn != InvalidXLogRecPtr);
2078 
2079  /* Already processed? */
2081  {
2082  if (fromdisk)
2083  {
2084  ereport(WARNING,
2085  (errmsg("removing stale two-phase state file for transaction %u",
2086  xid)));
2087  RemoveTwoPhaseFile(xid, true);
2088  }
2089  else
2090  {
2091  ereport(WARNING,
2092  (errmsg("removing stale two-phase state from memory for transaction %u",
2093  xid)));
2094  PrepareRedoRemove(xid, true);
2095  }
2096  return NULL;
2097  }
2098 
2099  /* Reject XID if too new */
2100  if (TransactionIdFollowsOrEquals(xid, origNextXid))
2101  {
2102  if (fromdisk)
2103  {
2104  ereport(WARNING,
2105  (errmsg("removing future two-phase state file for transaction %u",
2106  xid)));
2107  RemoveTwoPhaseFile(xid, true);
2108  }
2109  else
2110  {
2111  ereport(WARNING,
2112  (errmsg("removing future two-phase state from memory for transaction %u",
2113  xid)));
2114  PrepareRedoRemove(xid, true);
2115  }
2116  return NULL;
2117  }
2118 
2119  if (fromdisk)
2120  {
2121  /* Read and validate file */
2122  buf = ReadTwoPhaseFile(xid, false);
2123  }
2124  else
2125  {
2126  /* Read xlog data */
2127  XlogReadTwoPhaseData(prepare_start_lsn, &buf, NULL);
2128  }
2129 
2130  /* Deconstruct header */
2131  hdr = (TwoPhaseFileHeader *) buf;
2132  if (!TransactionIdEquals(hdr->xid, xid))
2133  {
2134  if (fromdisk)
2135  ereport(ERROR,
2137  errmsg("corrupted two-phase state file for transaction %u",
2138  xid)));
2139  else
2140  ereport(ERROR,
2142  errmsg("corrupted two-phase state in memory for transaction %u",
2143  xid)));
2144  }
2145 
2146  /*
2147  * Examine subtransaction XIDs ... they should all follow main XID, and
2148  * they may force us to advance nextFullXid.
2149  */
2150  subxids = (TransactionId *) (buf +
2151  MAXALIGN(sizeof(TwoPhaseFileHeader)) +
2152  MAXALIGN(hdr->gidlen));
2153  for (i = 0; i < hdr->nsubxacts; i++)
2154  {
2155  TransactionId subxid = subxids[i];
2156 
2157  Assert(TransactionIdFollows(subxid, xid));
2158 
2159  /* update nextFullXid if needed */
2160  if (setNextXid)
2162 
2163  if (setParent)
2164  SubTransSetParent(subxid, xid);
2165  }
2166 
2167  return buf;
2168 }
2169 
2170 
2171 /*
2172  * RecordTransactionCommitPrepared
2173  *
2174  * This is basically the same as RecordTransactionCommit (q.v. if you change
2175  * this function): in particular, we must set the delayChkpt flag to avoid a
2176  * race condition.
2177  *
2178  * We know the transaction made at least one XLOG entry (its PREPARE),
2179  * so it is never possible to optimize out the commit record.
2180  */
2181 static void
2183  int nchildren,
2184  TransactionId *children,
2185  int nrels,
2186  RelFileNode *rels,
2187  int ninvalmsgs,
2188  SharedInvalidationMessage *invalmsgs,
2189  bool initfileinval,
2190  const char *gid)
2191 {
2192  XLogRecPtr recptr;
2193  TimestampTz committs = GetCurrentTimestamp();
2194  bool replorigin;
2195 
2196  /*
2197  * Are we using the replication origins feature? Or, in other words, are
2198  * we replaying remote actions?
2199  */
2200  replorigin = (replorigin_session_origin != InvalidRepOriginId &&
2202 
2204 
2205  /* See notes in RecordTransactionCommit */
2206  MyPgXact->delayChkpt = true;
2207 
2208  /*
2209  * Emit the XLOG commit record. Note that we mark 2PC commits as
2210  * potentially having AccessExclusiveLocks since we don't know whether or
2211  * not they do.
2212  */
2213  recptr = XactLogCommitRecord(committs,
2214  nchildren, children, nrels, rels,
2215  ninvalmsgs, invalmsgs,
2216  initfileinval, false,
2218  xid, gid);
2219 
2220 
2221  if (replorigin)
2222  /* Move LSNs forward for this replication origin */
2224  XactLastRecEnd);
2225 
2226  /*
2227  * Record commit timestamp. The value comes from plain commit timestamp
2228  * if replorigin is not enabled, or replorigin already set a value for us
2229  * in replorigin_session_origin_timestamp otherwise.
2230  *
2231  * We don't need to WAL-log anything here, as the commit record written
2232  * above already contains the data.
2233  */
2234  if (!replorigin || replorigin_session_origin_timestamp == 0)
2236 
2237  TransactionTreeSetCommitTsData(xid, nchildren, children,
2239  replorigin_session_origin, false);
2240 
2241  /*
2242  * We don't currently try to sleep before flush here ... nor is there any
2243  * support for async commit of a prepared xact (the very idea is probably
2244  * a contradiction)
2245  */
2246 
2247  /* Flush XLOG to disk */
2248  XLogFlush(recptr);
2249 
2250  /* Mark the transaction committed in pg_xact */
2251  TransactionIdCommitTree(xid, nchildren, children);
2252 
2253  /* Checkpoint can proceed now */
2254  MyPgXact->delayChkpt = false;
2255 
2256  END_CRIT_SECTION();
2257 
2258  /*
2259  * Wait for synchronous replication, if required.
2260  *
2261  * Note that at this stage we have marked clog, but still show as running
2262  * in the procarray and continue to hold locks.
2263  */
2264  SyncRepWaitForLSN(recptr, true);
2265 }
2266 
2267 /*
2268  * RecordTransactionAbortPrepared
2269  *
2270  * This is basically the same as RecordTransactionAbort.
2271  *
2272  * We know the transaction made at least one XLOG entry (its PREPARE),
2273  * so it is never possible to optimize out the abort record.
2274  */
2275 static void
2277  int nchildren,
2278  TransactionId *children,
2279  int nrels,
2280  RelFileNode *rels,
2281  const char *gid)
2282 {
2283  XLogRecPtr recptr;
2284 
2285  /*
2286  * Catch the scenario where we aborted partway through
2287  * RecordTransactionCommitPrepared ...
2288  */
2289  if (TransactionIdDidCommit(xid))
2290  elog(PANIC, "cannot abort transaction %u, it was already committed",
2291  xid);
2292 
2294 
2295  /*
2296  * Emit the XLOG commit record. Note that we mark 2PC aborts as
2297  * potentially having AccessExclusiveLocks since we don't know whether or
2298  * not they do.
2299  */
2301  nchildren, children,
2302  nrels, rels,
2304  xid, gid);
2305 
2306  /* Always flush, since we're about to remove the 2PC state file */
2307  XLogFlush(recptr);
2308 
2309  /*
2310  * Mark the transaction aborted in clog. This is not absolutely necessary
2311  * but we may as well do it while we are here.
2312  */
2313  TransactionIdAbortTree(xid, nchildren, children);
2314 
2315  END_CRIT_SECTION();
2316 
2317  /*
2318  * Wait for synchronous replication, if required.
2319  *
2320  * Note that at this stage we have marked clog, but still show as running
2321  * in the procarray and continue to hold locks.
2322  */
2323  SyncRepWaitForLSN(recptr, false);
2324 }
2325 
2326 /*
2327  * PrepareRedoAdd
2328  *
2329  * Store pointers to the start/end of the WAL record along with the xid in
2330  * a gxact entry in shared memory TwoPhaseState structure. If caller
2331  * specifies InvalidXLogRecPtr as WAL location to fetch the two-phase
2332  * data, the entry is marked as located on disk.
2333  */
2334 void
2335 PrepareRedoAdd(char *buf, XLogRecPtr start_lsn,
2336  XLogRecPtr end_lsn, RepOriginId origin_id)
2337 {
2338  TwoPhaseFileHeader *hdr = (TwoPhaseFileHeader *) buf;
2339  char *bufptr;
2340  const char *gid;
2341  GlobalTransaction gxact;
2342 
2343  Assert(LWLockHeldByMeInMode(TwoPhaseStateLock, LW_EXCLUSIVE));
2345 
2346  bufptr = buf + MAXALIGN(sizeof(TwoPhaseFileHeader));
2347  gid = (const char *) bufptr;
2348 
2349  /*
2350  * Reserve the GID for the given transaction in the redo code path.
2351  *
2352  * This creates a gxact struct and puts it into the active array.
2353  *
2354  * In redo, this struct is mainly used to track PREPARE/COMMIT entries in
2355  * shared memory. Hence, we only fill up the bare minimum contents here.
2356  * The gxact also gets marked with gxact->inredo set to true to indicate
2357  * that it got added in the redo phase
2358  */
2359 
2360  /* Get a free gxact from the freelist */
2361  if (TwoPhaseState->freeGXacts == NULL)
2362  ereport(ERROR,
2363  (errcode(ERRCODE_OUT_OF_MEMORY),
2364  errmsg("maximum number of prepared transactions reached"),
2365  errhint("Increase max_prepared_transactions (currently %d).",
2366  max_prepared_xacts)));
2367  gxact = TwoPhaseState->freeGXacts;
2368  TwoPhaseState->freeGXacts = gxact->next;
2369 
2370  gxact->prepared_at = hdr->prepared_at;
2371  gxact->prepare_start_lsn = start_lsn;
2372  gxact->prepare_end_lsn = end_lsn;
2373  gxact->xid = hdr->xid;
2374  gxact->owner = hdr->owner;
2376  gxact->valid = false;
2377  gxact->ondisk = XLogRecPtrIsInvalid(start_lsn);
2378  gxact->inredo = true; /* yes, added in redo */
2379  strcpy(gxact->gid, gid);
2380 
2381  /* And insert it into the active array */
2382  Assert(TwoPhaseState->numPrepXacts < max_prepared_xacts);
2383  TwoPhaseState->prepXacts[TwoPhaseState->numPrepXacts++] = gxact;
2384 
2385  if (origin_id != InvalidRepOriginId)
2386  {
2387  /* recover apply progress */
2388  replorigin_advance(origin_id, hdr->origin_lsn, end_lsn,
2389  false /* backward */ , false /* WAL */ );
2390  }
2391 
2392  elog(DEBUG2, "added 2PC data in shared memory for transaction %u", gxact->xid);
2393 }
2394 
2395 /*
2396  * PrepareRedoRemove
2397  *
2398  * Remove the corresponding gxact entry from TwoPhaseState. Also remove
2399  * the 2PC file if a prepared transaction was saved via an earlier checkpoint.
2400  *
2401  * Caller must hold TwoPhaseStateLock in exclusive mode, because TwoPhaseState
2402  * is updated.
2403  */
2404 void
2406 {
2407  GlobalTransaction gxact = NULL;
2408  int i;
2409  bool found = false;
2410 
2411  Assert(LWLockHeldByMeInMode(TwoPhaseStateLock, LW_EXCLUSIVE));
2413 
2414  for (i = 0; i < TwoPhaseState->numPrepXacts; i++)
2415  {
2416  gxact = TwoPhaseState->prepXacts[i];
2417 
2418  if (gxact->xid == xid)
2419  {
2420  Assert(gxact->inredo);
2421  found = true;
2422  break;
2423  }
2424  }
2425 
2426  /*
2427  * Just leave if there is nothing, this is expected during WAL replay.
2428  */
2429  if (!found)
2430  return;
2431 
2432  /*
2433  * And now we can clean up any files we may have left.
2434  */
2435  elog(DEBUG2, "removing 2PC data for transaction %u", xid);
2436  if (gxact->ondisk)
2437  RemoveTwoPhaseFile(xid, giveWarning);
2438  RemoveGXact(gxact);
2439 }
int32 ninvalmsgs
Definition: xact.h:306
void TransactionIdAbortTree(TransactionId xid, int nxids, TransactionId *xids)
Definition: transam.c:290
#define INIT_CRC32C(crc)
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int xactGetCommittedChildren(TransactionId **ptr)
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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, const char *gid)
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XLogRecPtr XactLogCommitRecord(TimestampTz commit_time, int nsubxacts, TransactionId *subxacts, int nrels, RelFileNode *rels, int nmsgs, SharedInvalidationMessage *msgs, bool relcacheInval, bool forceSync, int xactflags, TransactionId twophase_xid, const char *twophase_gid)
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Size mul_size(Size s1, Size s2)
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const TwoPhaseCallback twophase_postabort_callbacks[TWOPHASE_RM_MAX_ID+1]
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struct StateFileChunk StateFileChunk
Size add_size(Size s1, Size s2)
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Definition: backendid.h:21
Oid MyDatabaseId
Definition: globals.c:85
static char * ProcessTwoPhaseBuffer(TransactionId xid, XLogRecPtr prepare_start_lsn, bool fromdisk, bool setParent, bool setNextXid)
Definition: twophase.c:2062
void RelationCacheInitFilePostInvalidate(void)
Definition: relcache.c:6014
bool overflowed
Definition: proc.h:234
void PrepareRedoAdd(char *buf, XLogRecPtr start_lsn, XLogRecPtr end_lsn, RepOriginId origin_id)
Definition: twophase.c:2335
int waitStatus
Definition: proc.h:102
static void RemoveTwoPhaseFile(TransactionId xid, bool giveWarning)
Definition: twophase.c:1596
#define PGPROC_MAX_CACHED_SUBXIDS
Definition: proc.h:36
#define InvalidOid
Definition: postgres_ext.h:36
#define TWOPHASE_MAGIC
Definition: twophase.c:911
void FinishPreparedTransaction(const char *gid, bool isCommit)
Definition: twophase.c:1399
struct GlobalTransactionData GlobalTransactionData
bool initfileinval
Definition: xact.h:307
#define Max(x, y)
Definition: c.h:905
TransactionId xids[PGPROC_MAX_CACHED_SUBXIDS]
Definition: proc.h:40
StateFileChunk * head
Definition: twophase.c:942
void RelationCacheInitFilePreInvalidate(void)
Definition: relcache.c:5989
uint64 XLogRecPtr
Definition: xlogdefs.h:21
#define Assert(condition)
Definition: c.h:739
RepOriginId replorigin_session_origin
Definition: origin.c:152
struct dirent * ReadDir(DIR *dir, const char *dirname)
Definition: fd.c:2569
void EndPrepare(GlobalTransaction gxact)
Definition: twophase.c:1060
TimestampTz origin_timestamp
Definition: xact.h:310
MemoryContext multi_call_memory_ctx
Definition: funcapi.h:101
size_t Size
Definition: c.h:467
static void pgstat_report_wait_start(uint32 wait_event_info)
Definition: pgstat.h:1318
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:1170
#define XLOG_XACT_OPMASK
Definition: xact.h:153
bool LWLockAcquire(LWLock *lock, LWLockMode mode)
Definition: lwlock.c:1122
#define MAXALIGN(LEN)
Definition: c.h:692
#define HeapTupleGetDatum(tuple)
Definition: funcapi.h:220
void SendSharedInvalidMessages(const SharedInvalidationMessage *msgs, int n)
Definition: sinval.c:49
static void save_state_data(const void *data, uint32 len)
Definition: twophase.c:959
void * repalloc(void *pointer, Size size)
Definition: mcxt.c:1069
static void MarkAsPrepared(GlobalTransaction gxact, bool lock_held)
Definition: twophase.c:536
TransactionId xid
Definition: xact.h:299
#define InvalidRepOriginId
Definition: origin.h:33
#define TWOPHASE_DIR
Definition: twophase.c:114
TransactionId xid
Definition: twophase.c:165
XLogReaderState * XLogReaderAllocate(int wal_segment_size, const char *waldir, XLogPageReadCB pagereadfunc, void *private_data)
Definition: xlogreader.c:73
static Datum values[MAXATTR]
Definition: bootstrap.c:167
TimestampTz prepared_at
Definition: twophase.c:154
void SHMQueueElemInit(SHM_QUEUE *queue)
Definition: shmqueue.c:57
static void XlogReadTwoPhaseData(XLogRecPtr lsn, char **buf, int *len)
Definition: twophase.c:1327
int pgprocno
Definition: proc.h:110
static char * user
Definition: pg_regress.c:94
void * user_fctx
Definition: funcapi.h:82
void restoreTwoPhaseData(void)
Definition: twophase.c:1777
uint32 magic
Definition: xact.h:297
void * palloc(Size size)
Definition: mcxt.c:949
int errmsg(const char *fmt,...)
Definition: elog.c:822
void SHMQueueInit(SHM_QUEUE *queue)
Definition: shmqueue.c:36
int xactGetCommittedInvalidationMessages(SharedInvalidationMessage **msgs, bool *RelcacheInitFileInval)
Definition: inval.c:828
static GlobalTransaction MyLockedGxact
Definition: twophase.c:199
#define HOLD_INTERRUPTS()
Definition: miscadmin.h:116
#define elog(elevel,...)
Definition: elog.h:228
void PostPrepare_Twophase(void)
Definition: twophase.c:357
int i
#define CStringGetTextDatum(s)
Definition: builtins.h:83
void * arg
#define PG_FUNCTION_ARGS
Definition: fmgr.h:188
TimestampTz prepared_at
Definition: xact.h:301
PGPROC * allProcs
Definition: proc.h:247
int pg_fsync(int fd)
Definition: fd.c:330
void CheckPointTwoPhase(XLogRecPtr redo_horizon)
Definition: twophase.c:1695
SHM_QUEUE myProcLocks[NUM_LOCK_PARTITIONS]
Definition: proc.h:160
char d_name[MAX_PATH]
Definition: dirent.h:14
xl_xact_prepare TwoPhaseFileHeader
Definition: twophase.c:913
#define TransactionIdIsValid(xid)
Definition: transam.h:41
void StandbyRecoverPreparedTransactions(void)
Definition: twophase.c:1920
static void static void status(const char *fmt,...) pg_attribute_printf(1
Definition: pg_regress.c:226
static void AtProcExit_Twophase(int code, Datum arg)
Definition: twophase.c:307
void SubTransSetParent(TransactionId xid, TransactionId parent)
Definition: subtrans.c:74
#define COMP_CRC32C(crc, data, len)
Definition: pg_crc32c.h:89
void RecoverPreparedTransactions(void)
Definition: twophase.c:1961
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
int read_local_xlog_page(XLogReaderState *state, XLogRecPtr targetPagePtr, int reqLen, XLogRecPtr targetRecPtr, char *cur_page)
Definition: xlogutils.c:817
#define ERRCODE_DUPLICATE_OBJECT
Definition: streamutil.c:31
Definition: proc.h:95
void(* TwoPhaseCallback)(TransactionId xid, uint16 info, void *recdata, uint32 len)
Definition: twophase_rmgr.h:17
#define FIN_CRC32C(crc)
Definition: pg_crc32c.h:94
int pid
Definition: proc.h:109
int16 AttrNumber
Definition: attnum.h:21
XLogRecPtr prepare_end_lsn
Definition: twophase.c:164
void ProcArrayAdd(PGPROC *proc)
Definition: procarray.c:277
#define read(a, b, c)
Definition: win32.h:13
int FreeDir(DIR *dir)
Definition: fd.c:2621
#define offsetof(type, field)
Definition: c.h:662
BackendId dummyBackendId
Definition: twophase.c:153
#define NUM_LOCK_PARTITIONS
Definition: lwlock.h:117
#define XLogRecGetRmid(decoder)
Definition: xlogreader.h:280
static void RecordTransactionCommitPrepared(TransactionId xid, int nchildren, TransactionId *children, int nrels, RelFileNode *rels, int ninvalmsgs, SharedInvalidationMessage *invalmsgs, bool initfileinval, const char *gid)
Definition: twophase.c:2182
#define SRF_RETURN_DONE(_funcctx)
Definition: funcapi.h:306
LocalTransactionId lxid
Definition: proc.h:106
#define SRF_FIRSTCALL_INIT()
Definition: funcapi.h:284
TwoPhaseRmgrId rmid
Definition: twophase.c:924