/*------------------------------------------------------------------------- * * twophase.c * Two-phase commit support functions. * * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * * IDENTIFICATION * $PostgreSQL: pgsql/src/backend/access/transam/twophase.c,v 1.41 2008/03/25 22:42:42 tgl Exp $ * * NOTES * Each global transaction is associated with a global transaction * identifier (GID). The client assigns a GID to a postgres * transaction with the PREPARE TRANSACTION command. * * We keep all active global transactions in a shared memory array. * When the PREPARE TRANSACTION command is issued, the GID is * reserved for the transaction in the array. This is done before * a WAL entry is made, because the reservation checks for duplicate * GIDs and aborts the transaction if there already is a global * transaction in prepared state with the same GID. * * A global transaction (gxact) also has a dummy PGPROC that is entered * into the ProcArray array; this is what keeps the XID considered * running by TransactionIdIsInProgress. It is also convenient as a * PGPROC to hook the gxact's locks to. * * In order to survive crashes and shutdowns, all prepared * transactions must be stored in permanent storage. This includes * locking information, pending notifications etc. All that state * information is written to the per-transaction state file in * the pg_twophase directory. * *------------------------------------------------------------------------- */ #include "postgres.h" #include #include #include #include #include #include "access/heapam.h" #include "access/subtrans.h" #include "access/transam.h" #include "access/twophase.h" #include "access/twophase_rmgr.h" #include "access/xact.h" #include "catalog/pg_type.h" #include "funcapi.h" #include "miscadmin.h" #include "pgstat.h" #include "storage/fd.h" #include "storage/procarray.h" #include "storage/smgr.h" #include "utils/builtins.h" /* * Directory where Two-phase commit files reside within PGDATA */ #define TWOPHASE_DIR "pg_twophase" /* GUC variable, can't be changed after startup */ int max_prepared_xacts = 5; /* * This struct describes one global transaction that is in prepared state * or attempting to become prepared. * * The first component of the struct is a dummy PGPROC that is inserted * into the global ProcArray so that the transaction appears to still be * running and holding locks. It must be first because we cast pointers * to PGPROC and pointers to GlobalTransactionData back and forth. * * The lifecycle of a global transaction is: * * 1. After checking that the requested GID is not in use, set up an * entry in the TwoPhaseState->prepXacts array with the correct XID and GID, * with locking_xid = my own XID and valid = false. * * 2. After successfully completing prepare, set valid = true and enter the * contained PGPROC into the global ProcArray. * * 3. To begin COMMIT PREPARED or ROLLBACK PREPARED, check that the entry * is valid and its locking_xid is no longer active, then store my current * XID into locking_xid. This prevents concurrent attempts to commit or * rollback the same prepared xact. * * 4. On completion of COMMIT PREPARED or ROLLBACK PREPARED, remove the entry * from the ProcArray and the TwoPhaseState->prepXacts array and return it to * the freelist. * * Note that if the preparing transaction fails between steps 1 and 2, the * entry will remain in prepXacts until recycled. We can detect recyclable * entries by checking for valid = false and locking_xid no longer active. * * typedef struct GlobalTransactionData *GlobalTransaction appears in * twophase.h */ #define GIDSIZE 200 typedef struct GlobalTransactionData { PGPROC proc; /* dummy proc */ TimestampTz prepared_at; /* time of preparation */ XLogRecPtr prepare_lsn; /* XLOG offset of prepare record */ Oid owner; /* ID of user that executed the xact */ TransactionId locking_xid; /* top-level XID of backend working on xact */ bool valid; /* TRUE if fully prepared */ char gid[GIDSIZE]; /* The GID assigned to the prepared xact */ } GlobalTransactionData; /* * Two Phase Commit shared state. Access to this struct is protected * by TwoPhaseStateLock. */ typedef struct TwoPhaseStateData { /* Head of linked list of free GlobalTransactionData structs */ SHMEM_OFFSET freeGXacts; /* Number of valid prepXacts entries. */ int numPrepXacts; /* * There are max_prepared_xacts items in this array, but C wants a * fixed-size array. */ GlobalTransaction prepXacts[1]; /* VARIABLE LENGTH ARRAY */ } TwoPhaseStateData; /* VARIABLE LENGTH STRUCT */ static TwoPhaseStateData *TwoPhaseState; static void RecordTransactionCommitPrepared(TransactionId xid, int nchildren, TransactionId *children, int nrels, RelFileNode *rels); static void RecordTransactionAbortPrepared(TransactionId xid, int nchildren, TransactionId *children, int nrels, RelFileNode *rels); static void ProcessRecords(char *bufptr, TransactionId xid, const TwoPhaseCallback callbacks[]); /* * Initialization of shared memory */ Size TwoPhaseShmemSize(void) { Size size; /* Need the fixed struct, the array of pointers, and the GTD structs */ size = offsetof(TwoPhaseStateData, prepXacts); size = add_size(size, mul_size(max_prepared_xacts, sizeof(GlobalTransaction))); size = MAXALIGN(size); size = add_size(size, mul_size(max_prepared_xacts, sizeof(GlobalTransactionData))); return size; } void TwoPhaseShmemInit(void) { bool found; TwoPhaseState = ShmemInitStruct("Prepared Transaction Table", TwoPhaseShmemSize(), &found); if (!IsUnderPostmaster) { GlobalTransaction gxacts; int i; Assert(!found); TwoPhaseState->freeGXacts = INVALID_OFFSET; TwoPhaseState->numPrepXacts = 0; /* * Initialize the linked list of free GlobalTransactionData structs */ gxacts = (GlobalTransaction) ((char *) TwoPhaseState + MAXALIGN(offsetof(TwoPhaseStateData, prepXacts) + sizeof(GlobalTransaction) * max_prepared_xacts)); for (i = 0; i < max_prepared_xacts; i++) { gxacts[i].proc.links.next = TwoPhaseState->freeGXacts; TwoPhaseState->freeGXacts = MAKE_OFFSET(&gxacts[i]); } } else Assert(found); } /* * MarkAsPreparing * Reserve the GID for the given transaction. * * Internally, this creates a gxact struct and puts it into the active array. * NOTE: this is also used when reloading a gxact after a crash; so avoid * assuming that we can use very much backend context. */ GlobalTransaction MarkAsPreparing(TransactionId xid, const char *gid, TimestampTz prepared_at, Oid owner, Oid databaseid) { GlobalTransaction gxact; int i; if (strlen(gid) >= GIDSIZE) ereport(ERROR, (errcode(ERRCODE_INVALID_PARAMETER_VALUE), errmsg("transaction identifier \"%s\" is too long", gid))); LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE); /* * First, find and recycle any gxacts that failed during prepare. We do * this partly to ensure we don't mistakenly say their GIDs are still * reserved, and partly so we don't fail on out-of-slots unnecessarily. */ for (i = 0; i < TwoPhaseState->numPrepXacts; i++) { gxact = TwoPhaseState->prepXacts[i]; if (!gxact->valid && !TransactionIdIsActive(gxact->locking_xid)) { /* It's dead Jim ... remove from the active array */ TwoPhaseState->numPrepXacts--; TwoPhaseState->prepXacts[i] = TwoPhaseState->prepXacts[TwoPhaseState->numPrepXacts]; /* and put it back in the freelist */ gxact->proc.links.next = TwoPhaseState->freeGXacts; TwoPhaseState->freeGXacts = MAKE_OFFSET(gxact); /* Back up index count too, so we don't miss scanning one */ i--; } } /* Check for conflicting GID */ for (i = 0; i < TwoPhaseState->numPrepXacts; i++) { gxact = TwoPhaseState->prepXacts[i]; if (strcmp(gxact->gid, gid) == 0) { ereport(ERROR, (errcode(ERRCODE_DUPLICATE_OBJECT), errmsg("transaction identifier \"%s\" is already in use", gid))); } } /* Get a free gxact from the freelist */ if (TwoPhaseState->freeGXacts == INVALID_OFFSET) ereport(ERROR, (errcode(ERRCODE_OUT_OF_MEMORY), errmsg("maximum number of prepared transactions reached"), errhint("Increase max_prepared_transactions (currently %d).", max_prepared_xacts))); gxact = (GlobalTransaction) MAKE_PTR(TwoPhaseState->freeGXacts); TwoPhaseState->freeGXacts = gxact->proc.links.next; /* Initialize it */ MemSet(&gxact->proc, 0, sizeof(PGPROC)); SHMQueueElemInit(&(gxact->proc.links)); gxact->proc.waitStatus = STATUS_OK; /* We set up the gxact's VXID as InvalidBackendId/XID */ gxact->proc.lxid = (LocalTransactionId) xid; gxact->proc.xid = xid; gxact->proc.xmin = InvalidTransactionId; gxact->proc.pid = 0; gxact->proc.backendId = InvalidBackendId; gxact->proc.databaseId = databaseid; gxact->proc.roleId = owner; gxact->proc.inCommit = false; gxact->proc.vacuumFlags = 0; gxact->proc.lwWaiting = false; gxact->proc.lwExclusive = false; gxact->proc.lwWaitLink = NULL; gxact->proc.waitLock = NULL; gxact->proc.waitProcLock = NULL; for (i = 0; i < NUM_LOCK_PARTITIONS; i++) SHMQueueInit(&(gxact->proc.myProcLocks[i])); /* subxid data must be filled later by GXactLoadSubxactData */ gxact->proc.subxids.overflowed = false; gxact->proc.subxids.nxids = 0; gxact->prepared_at = prepared_at; /* initialize LSN to 0 (start of WAL) */ gxact->prepare_lsn.xlogid = 0; gxact->prepare_lsn.xrecoff = 0; gxact->owner = owner; gxact->locking_xid = xid; gxact->valid = false; strcpy(gxact->gid, gid); /* And insert it into the active array */ Assert(TwoPhaseState->numPrepXacts < max_prepared_xacts); TwoPhaseState->prepXacts[TwoPhaseState->numPrepXacts++] = gxact; LWLockRelease(TwoPhaseStateLock); return gxact; } /* * GXactLoadSubxactData * * If the transaction being persisted had any subtransactions, this must * be called before MarkAsPrepared() to load information into the dummy * PGPROC. */ static void GXactLoadSubxactData(GlobalTransaction gxact, int nsubxacts, TransactionId *children) { /* We need no extra lock since the GXACT isn't valid yet */ if (nsubxacts > PGPROC_MAX_CACHED_SUBXIDS) { gxact->proc.subxids.overflowed = true; nsubxacts = PGPROC_MAX_CACHED_SUBXIDS; } if (nsubxacts > 0) { memcpy(gxact->proc.subxids.xids, children, nsubxacts * sizeof(TransactionId)); gxact->proc.subxids.nxids = nsubxacts; } } /* * MarkAsPrepared * Mark the GXACT as fully valid, and enter it into the global ProcArray. */ static void MarkAsPrepared(GlobalTransaction gxact) { /* Lock here may be overkill, but I'm not convinced of that ... */ LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE); Assert(!gxact->valid); gxact->valid = true; LWLockRelease(TwoPhaseStateLock); /* * Put it into the global ProcArray so TransactionIdIsInProgress considers * the XID as still running. */ ProcArrayAdd(&gxact->proc); } /* * LockGXact * Locate the prepared transaction and mark it busy for COMMIT or PREPARE. */ static GlobalTransaction LockGXact(const char *gid, Oid user) { int i; LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE); for (i = 0; i < TwoPhaseState->numPrepXacts; i++) { GlobalTransaction gxact = TwoPhaseState->prepXacts[i]; /* Ignore not-yet-valid GIDs */ if (!gxact->valid) continue; if (strcmp(gxact->gid, gid) != 0) continue; /* Found it, but has someone else got it locked? */ if (TransactionIdIsValid(gxact->locking_xid)) { if (TransactionIdIsActive(gxact->locking_xid)) ereport(ERROR, (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE), errmsg("prepared transaction with identifier \"%s\" is busy", gid))); gxact->locking_xid = InvalidTransactionId; } if (user != gxact->owner && !superuser_arg(user)) ereport(ERROR, (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE), errmsg("permission denied to finish prepared transaction"), errhint("Must be superuser or the user that prepared the transaction."))); /* * Note: it probably would be possible to allow committing from * another database; but at the moment NOTIFY is known not to work and * there may be some other issues as well. Hence disallow until * someone gets motivated to make it work. */ if (MyDatabaseId != gxact->proc.databaseId) ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED), errmsg("prepared transaction belongs to another database"), errhint("Connect to the database where the transaction was prepared to finish it."))); /* OK for me to lock it */ gxact->locking_xid = GetTopTransactionId(); LWLockRelease(TwoPhaseStateLock); return gxact; } LWLockRelease(TwoPhaseStateLock); ereport(ERROR, (errcode(ERRCODE_UNDEFINED_OBJECT), errmsg("prepared transaction with identifier \"%s\" does not exist", gid))); /* NOTREACHED */ return NULL; } /* * RemoveGXact * Remove the prepared transaction from the shared memory array. * * NB: caller should have already removed it from ProcArray */ static void RemoveGXact(GlobalTransaction gxact) { int i; LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE); for (i = 0; i < TwoPhaseState->numPrepXacts; i++) { if (gxact == TwoPhaseState->prepXacts[i]) { /* remove from the active array */ TwoPhaseState->numPrepXacts--; TwoPhaseState->prepXacts[i] = TwoPhaseState->prepXacts[TwoPhaseState->numPrepXacts]; /* and put it back in the freelist */ gxact->proc.links.next = TwoPhaseState->freeGXacts; TwoPhaseState->freeGXacts = MAKE_OFFSET(gxact); LWLockRelease(TwoPhaseStateLock); return; } } LWLockRelease(TwoPhaseStateLock); elog(ERROR, "failed to find %p in GlobalTransaction array", gxact); } /* * TransactionIdIsPrepared * True iff transaction associated with the identifier is prepared * for two-phase commit * * Note: only gxacts marked "valid" are considered; but notice we do not * check the locking status. * * This is not currently exported, because it is only needed internally. */ static bool TransactionIdIsPrepared(TransactionId xid) { bool result = false; int i; LWLockAcquire(TwoPhaseStateLock, LW_SHARED); for (i = 0; i < TwoPhaseState->numPrepXacts; i++) { GlobalTransaction gxact = TwoPhaseState->prepXacts[i]; if (gxact->valid && gxact->proc.xid == xid) { result = true; break; } } LWLockRelease(TwoPhaseStateLock); return result; } /* * Returns an array of all prepared transactions for the user-level * function pg_prepared_xact. * * The returned array and all its elements are copies of internal data * structures, to minimize the time we need to hold the TwoPhaseStateLock. * * WARNING -- we return even those transactions that are not fully prepared * yet. The caller should filter them out if he doesn't want them. * * The returned array is palloc'd. */ static int GetPreparedTransactionList(GlobalTransaction *gxacts) { GlobalTransaction array; int num; int i; LWLockAcquire(TwoPhaseStateLock, LW_SHARED); if (TwoPhaseState->numPrepXacts == 0) { LWLockRelease(TwoPhaseStateLock); *gxacts = NULL; return 0; } num = TwoPhaseState->numPrepXacts; array = (GlobalTransaction) palloc(sizeof(GlobalTransactionData) * num); *gxacts = array; for (i = 0; i < num; i++) memcpy(array + i, TwoPhaseState->prepXacts[i], sizeof(GlobalTransactionData)); LWLockRelease(TwoPhaseStateLock); return num; } /* Working status for pg_prepared_xact */ typedef struct { GlobalTransaction array; int ngxacts; int currIdx; } Working_State; /* * pg_prepared_xact * Produce a view with one row per prepared transaction. * * This function is here so we don't have to export the * GlobalTransactionData struct definition. */ Datum pg_prepared_xact(PG_FUNCTION_ARGS) { FuncCallContext *funcctx; Working_State *status; if (SRF_IS_FIRSTCALL()) { TupleDesc tupdesc; MemoryContext oldcontext; /* create a function context for cross-call persistence */ funcctx = SRF_FIRSTCALL_INIT(); /* * Switch to memory context appropriate for multiple function calls */ oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx); /* build tupdesc for result tuples */ /* this had better match pg_prepared_xacts view in system_views.sql */ tupdesc = CreateTemplateTupleDesc(5, false); TupleDescInitEntry(tupdesc, (AttrNumber) 1, "transaction", XIDOID, -1, 0); TupleDescInitEntry(tupdesc, (AttrNumber) 2, "gid", TEXTOID, -1, 0); TupleDescInitEntry(tupdesc, (AttrNumber) 3, "prepared", TIMESTAMPTZOID, -1, 0); TupleDescInitEntry(tupdesc, (AttrNumber) 4, "ownerid", OIDOID, -1, 0); TupleDescInitEntry(tupdesc, (AttrNumber) 5, "dbid", OIDOID, -1, 0); funcctx->tuple_desc = BlessTupleDesc(tupdesc); /* * Collect all the 2PC status information that we will format and send * out as a result set. */ status = (Working_State *) palloc(sizeof(Working_State)); funcctx->user_fctx = (void *) status; status->ngxacts = GetPreparedTransactionList(&status->array); status->currIdx = 0; MemoryContextSwitchTo(oldcontext); } funcctx = SRF_PERCALL_SETUP(); status = (Working_State *) funcctx->user_fctx; while (status->array != NULL && status->currIdx < status->ngxacts) { GlobalTransaction gxact = &status->array[status->currIdx++]; Datum values[5]; bool nulls[5]; HeapTuple tuple; Datum result; if (!gxact->valid) continue; /* * Form tuple with appropriate data. */ MemSet(values, 0, sizeof(values)); MemSet(nulls, 0, sizeof(nulls)); values[0] = TransactionIdGetDatum(gxact->proc.xid); values[1] = CStringGetTextDatum(gxact->gid); values[2] = TimestampTzGetDatum(gxact->prepared_at); values[3] = ObjectIdGetDatum(gxact->owner); values[4] = ObjectIdGetDatum(gxact->proc.databaseId); tuple = heap_form_tuple(funcctx->tuple_desc, values, nulls); result = HeapTupleGetDatum(tuple); SRF_RETURN_NEXT(funcctx, result); } SRF_RETURN_DONE(funcctx); } /* * TwoPhaseGetDummyProc * Get the PGPROC that represents a prepared transaction specified by XID */ PGPROC * TwoPhaseGetDummyProc(TransactionId xid) { PGPROC *result = NULL; int i; static TransactionId cached_xid = InvalidTransactionId; static PGPROC *cached_proc = NULL; /* * During a recovery, COMMIT PREPARED, or ABORT PREPARED, we'll be called * repeatedly for the same XID. We can save work with a simple cache. */ if (xid == cached_xid) return cached_proc; LWLockAcquire(TwoPhaseStateLock, LW_SHARED); for (i = 0; i < TwoPhaseState->numPrepXacts; i++) { GlobalTransaction gxact = TwoPhaseState->prepXacts[i]; if (gxact->proc.xid == xid) { result = &gxact->proc; break; } } LWLockRelease(TwoPhaseStateLock); if (result == NULL) /* should not happen */ elog(ERROR, "failed to find dummy PGPROC for xid %u", xid); cached_xid = xid; cached_proc = result; return result; } /************************************************************************/ /* State file support */ /************************************************************************/ #define TwoPhaseFilePath(path, xid) \ snprintf(path, MAXPGPATH, TWOPHASE_DIR "/%08X", xid) /* * 2PC state file format: * * 1. TwoPhaseFileHeader * 2. TransactionId[] (subtransactions) * 3. RelFileNode[] (files to be deleted at commit) * 4. RelFileNode[] (files to be deleted at abort) * 5. TwoPhaseRecordOnDisk * 6. ... * 7. TwoPhaseRecordOnDisk (end sentinel, rmid == TWOPHASE_RM_END_ID) * 8. CRC32 * * Each segment except the final CRC32 is MAXALIGN'd. */ /* * Header for a 2PC state file */ #define TWOPHASE_MAGIC 0x57F94531 /* format identifier */ typedef struct TwoPhaseFileHeader { uint32 magic; /* format identifier */ uint32 total_len; /* actual file length */ TransactionId xid; /* original transaction XID */ Oid database; /* OID of database it was in */ TimestampTz prepared_at; /* time of preparation */ Oid owner; /* user running the transaction */ int32 nsubxacts; /* number of following subxact XIDs */ int32 ncommitrels; /* number of delete-on-commit rels */ int32 nabortrels; /* number of delete-on-abort rels */ char gid[GIDSIZE]; /* GID for transaction */ } TwoPhaseFileHeader; /* * Header for each record in a state file * * NOTE: len counts only the rmgr data, not the TwoPhaseRecordOnDisk header. * The rmgr data will be stored starting on a MAXALIGN boundary. */ typedef struct TwoPhaseRecordOnDisk { uint32 len; /* length of rmgr data */ TwoPhaseRmgrId rmid; /* resource manager for this record */ uint16 info; /* flag bits for use by rmgr */ } TwoPhaseRecordOnDisk; /* * During prepare, the state file is assembled in memory before writing it * to WAL and the actual state file. We use a chain of XLogRecData blocks * so that we will be able to pass the state file contents directly to * XLogInsert. */ static struct xllist { XLogRecData *head; /* first data block in the chain */ XLogRecData *tail; /* last block in chain */ uint32 bytes_free; /* free bytes left in tail block */ uint32 total_len; /* total data bytes in chain */ } records; /* * Append a block of data to records data structure. * * NB: each block is padded to a MAXALIGN multiple. This must be * accounted for when the file is later read! * * The data is copied, so the caller is free to modify it afterwards. */ static void save_state_data(const void *data, uint32 len) { uint32 padlen = MAXALIGN(len); if (padlen > records.bytes_free) { records.tail->next = palloc0(sizeof(XLogRecData)); records.tail = records.tail->next; records.tail->buffer = InvalidBuffer; records.tail->len = 0; records.tail->next = NULL; records.bytes_free = Max(padlen, 512); records.tail->data = palloc(records.bytes_free); } memcpy(((char *) records.tail->data) + records.tail->len, data, len); records.tail->len += padlen; records.bytes_free -= padlen; records.total_len += padlen; } /* * Start preparing a state file. * * Initializes data structure and inserts the 2PC file header record. */ void StartPrepare(GlobalTransaction gxact) { TransactionId xid = gxact->proc.xid; TwoPhaseFileHeader hdr; TransactionId *children; RelFileNode *commitrels; RelFileNode *abortrels; /* Initialize linked list */ records.head = palloc0(sizeof(XLogRecData)); records.head->buffer = InvalidBuffer; records.head->len = 0; records.head->next = NULL; records.bytes_free = Max(sizeof(TwoPhaseFileHeader), 512); records.head->data = palloc(records.bytes_free); records.tail = records.head; records.total_len = 0; /* Create header */ hdr.magic = TWOPHASE_MAGIC; hdr.total_len = 0; /* EndPrepare will fill this in */ hdr.xid = xid; hdr.database = gxact->proc.databaseId; hdr.prepared_at = gxact->prepared_at; hdr.owner = gxact->owner; hdr.nsubxacts = xactGetCommittedChildren(&children); hdr.ncommitrels = smgrGetPendingDeletes(true, &commitrels, NULL); hdr.nabortrels = smgrGetPendingDeletes(false, &abortrels, NULL); StrNCpy(hdr.gid, gxact->gid, GIDSIZE); save_state_data(&hdr, sizeof(TwoPhaseFileHeader)); /* Add the additional info about subxacts and deletable files */ if (hdr.nsubxacts > 0) { save_state_data(children, hdr.nsubxacts * sizeof(TransactionId)); /* While we have the child-xact data, stuff it in the gxact too */ GXactLoadSubxactData(gxact, hdr.nsubxacts, children); } if (hdr.ncommitrels > 0) { save_state_data(commitrels, hdr.ncommitrels * sizeof(RelFileNode)); pfree(commitrels); } if (hdr.nabortrels > 0) { save_state_data(abortrels, hdr.nabortrels * sizeof(RelFileNode)); pfree(abortrels); } } /* * Finish preparing state file. * * Calculates CRC and writes state file to WAL and in pg_twophase directory. */ void EndPrepare(GlobalTransaction gxact) { TransactionId xid = gxact->proc.xid; TwoPhaseFileHeader *hdr; char path[MAXPGPATH]; XLogRecData *record; pg_crc32 statefile_crc; pg_crc32 bogus_crc; int fd; /* Add the end sentinel to the list of 2PC records */ RegisterTwoPhaseRecord(TWOPHASE_RM_END_ID, 0, NULL, 0); /* Go back and fill in total_len in the file header record */ hdr = (TwoPhaseFileHeader *) records.head->data; Assert(hdr->magic == TWOPHASE_MAGIC); hdr->total_len = records.total_len + sizeof(pg_crc32); /* * Create the 2PC state file. * * Note: because we use BasicOpenFile(), we are responsible for ensuring * the FD gets closed in any error exit path. Once we get into the * critical section, though, it doesn't matter since any failure causes * PANIC anyway. */ TwoPhaseFilePath(path, xid); fd = BasicOpenFile(path, O_CREAT | O_EXCL | O_WRONLY | PG_BINARY, S_IRUSR | S_IWUSR); if (fd < 0) ereport(ERROR, (errcode_for_file_access(), errmsg("could not create two-phase state file \"%s\": %m", path))); /* Write data to file, and calculate CRC as we pass over it */ INIT_CRC32(statefile_crc); for (record = records.head; record != NULL; record = record->next) { COMP_CRC32(statefile_crc, record->data, record->len); if ((write(fd, record->data, record->len)) != record->len) { close(fd); ereport(ERROR, (errcode_for_file_access(), errmsg("could not write two-phase state file: %m"))); } } FIN_CRC32(statefile_crc); /* * Write a deliberately bogus CRC to the state file; this is just paranoia * to catch the case where four more bytes will run us out of disk space. */ bogus_crc = ~statefile_crc; if ((write(fd, &bogus_crc, sizeof(pg_crc32))) != sizeof(pg_crc32)) { close(fd); ereport(ERROR, (errcode_for_file_access(), errmsg("could not write two-phase state file: %m"))); } /* Back up to prepare for rewriting the CRC */ if (lseek(fd, -((off_t) sizeof(pg_crc32)), SEEK_CUR) < 0) { close(fd); ereport(ERROR, (errcode_for_file_access(), errmsg("could not seek in two-phase state file: %m"))); } /* * The state file isn't valid yet, because we haven't written the correct * CRC yet. Before we do that, insert entry in WAL and flush it to disk. * * Between the time we have written the WAL entry and the time we write * out the correct state file CRC, we have an inconsistency: the xact is * prepared according to WAL but not according to our on-disk state. We * use a critical section to force a PANIC if we are unable to complete * the write --- then, WAL replay should repair the inconsistency. The * odds of a PANIC actually occurring should be very tiny given that we * were able to write the bogus CRC above. * * We have to set inCommit here, too; otherwise a checkpoint starting * immediately after the WAL record is inserted could complete without * fsync'ing our state file. (This is essentially the same kind of race * condition as the COMMIT-to-clog-write case that RecordTransactionCommit * uses inCommit for; see notes there.) * * We save the PREPARE record's location in the gxact for later use by * CheckPointTwoPhase. */ START_CRIT_SECTION(); MyProc->inCommit = true; gxact->prepare_lsn = XLogInsert(RM_XACT_ID, XLOG_XACT_PREPARE, records.head); XLogFlush(gxact->prepare_lsn); /* If we crash now, we have prepared: WAL replay will fix things */ /* write correct CRC and close file */ if ((write(fd, &statefile_crc, sizeof(pg_crc32))) != sizeof(pg_crc32)) { close(fd); ereport(ERROR, (errcode_for_file_access(), errmsg("could not write two-phase state file: %m"))); } if (close(fd) != 0) ereport(ERROR, (errcode_for_file_access(), errmsg("could not close two-phase state file: %m"))); /* * Mark the prepared transaction as valid. As soon as xact.c marks MyProc * as not running our XID (which it will do immediately after this * function returns), others can commit/rollback the xact. * * NB: a side effect of this is to make a dummy ProcArray entry for the * prepared XID. This must happen before we clear the XID from MyProc, * else there is a window where the XID is not running according to * TransactionIdIsInProgress, and onlookers would be entitled to assume * the xact crashed. Instead we have a window where the same XID appears * twice in ProcArray, which is OK. */ MarkAsPrepared(gxact); /* * Now we can mark ourselves as out of the commit critical section: a * checkpoint starting after this will certainly see the gxact as a * candidate for fsyncing. */ MyProc->inCommit = false; END_CRIT_SECTION(); records.tail = records.head = NULL; } /* * Register a 2PC record to be written to state file. */ void RegisterTwoPhaseRecord(TwoPhaseRmgrId rmid, uint16 info, const void *data, uint32 len) { TwoPhaseRecordOnDisk record; record.rmid = rmid; record.info = info; record.len = len; save_state_data(&record, sizeof(TwoPhaseRecordOnDisk)); if (len > 0) save_state_data(data, len); } /* * Read and validate the state file for xid. * * If it looks OK (has a valid magic number and CRC), return the palloc'd * contents of the file. Otherwise return NULL. */ static char * ReadTwoPhaseFile(TransactionId xid) { char path[MAXPGPATH]; char *buf; TwoPhaseFileHeader *hdr; int fd; struct stat stat; uint32 crc_offset; pg_crc32 calc_crc, file_crc; TwoPhaseFilePath(path, xid); fd = BasicOpenFile(path, O_RDONLY | PG_BINARY, 0); if (fd < 0) { ereport(WARNING, (errcode_for_file_access(), errmsg("could not open two-phase state file \"%s\": %m", path))); return NULL; } /* * Check file length. We can determine a lower bound pretty easily. We * set an upper bound mainly to avoid palloc() failure on a corrupt file. */ if (fstat(fd, &stat)) { close(fd); ereport(WARNING, (errcode_for_file_access(), errmsg("could not stat two-phase state file \"%s\": %m", path))); return NULL; } if (stat.st_size < (MAXALIGN(sizeof(TwoPhaseFileHeader)) + MAXALIGN(sizeof(TwoPhaseRecordOnDisk)) + sizeof(pg_crc32)) || stat.st_size > 10000000) { close(fd); return NULL; } crc_offset = stat.st_size - sizeof(pg_crc32); if (crc_offset != MAXALIGN(crc_offset)) { close(fd); return NULL; } /* * OK, slurp in the file. */ buf = (char *) palloc(stat.st_size); if (read(fd, buf, stat.st_size) != stat.st_size) { close(fd); ereport(WARNING, (errcode_for_file_access(), errmsg("could not read two-phase state file \"%s\": %m", path))); pfree(buf); return NULL; } close(fd); hdr = (TwoPhaseFileHeader *) buf; if (hdr->magic != TWOPHASE_MAGIC || hdr->total_len != stat.st_size) { pfree(buf); return NULL; } INIT_CRC32(calc_crc); COMP_CRC32(calc_crc, buf, crc_offset); FIN_CRC32(calc_crc); file_crc = *((pg_crc32 *) (buf + crc_offset)); if (!EQ_CRC32(calc_crc, file_crc)) { pfree(buf); return NULL; } return buf; } /* * FinishPreparedTransaction: execute COMMIT PREPARED or ROLLBACK PREPARED */ void FinishPreparedTransaction(const char *gid, bool isCommit) { GlobalTransaction gxact; TransactionId xid; char *buf; char *bufptr; TwoPhaseFileHeader *hdr; TransactionId latestXid; TransactionId *children; RelFileNode *commitrels; RelFileNode *abortrels; int i; /* * Validate the GID, and lock the GXACT to ensure that two backends do not * try to commit the same GID at once. */ gxact = LockGXact(gid, GetUserId()); xid = gxact->proc.xid; /* * Read and validate the state file */ buf = ReadTwoPhaseFile(xid); if (buf == NULL) ereport(ERROR, (errcode(ERRCODE_DATA_CORRUPTED), errmsg("two-phase state file for transaction %u is corrupt", xid))); /* * Disassemble the header area */ hdr = (TwoPhaseFileHeader *) buf; Assert(TransactionIdEquals(hdr->xid, xid)); bufptr = buf + MAXALIGN(sizeof(TwoPhaseFileHeader)); children = (TransactionId *) bufptr; bufptr += MAXALIGN(hdr->nsubxacts * sizeof(TransactionId)); commitrels = (RelFileNode *) bufptr; bufptr += MAXALIGN(hdr->ncommitrels * sizeof(RelFileNode)); abortrels = (RelFileNode *) bufptr; bufptr += MAXALIGN(hdr->nabortrels * sizeof(RelFileNode)); /* compute latestXid among all children */ latestXid = TransactionIdLatest(xid, hdr->nsubxacts, children); /* * The order of operations here is critical: make the XLOG entry for * commit or abort, then mark the transaction committed or aborted in * pg_clog, then remove its PGPROC from the global ProcArray (which means * TransactionIdIsInProgress will stop saying the prepared xact is in * progress), then run the post-commit or post-abort callbacks. The * callbacks will release the locks the transaction held. */ if (isCommit) RecordTransactionCommitPrepared(xid, hdr->nsubxacts, children, hdr->ncommitrels, commitrels); else RecordTransactionAbortPrepared(xid, hdr->nsubxacts, children, hdr->nabortrels, abortrels); ProcArrayRemove(&gxact->proc, latestXid); /* * In case we fail while running the callbacks, mark the gxact invalid so * no one else will try to commit/rollback, and so it can be recycled * properly later. It is still locked by our XID so it won't go away yet. * * (We assume it's safe to do this without taking TwoPhaseStateLock.) */ gxact->valid = false; /* * We have to remove any files that were supposed to be dropped. For * consistency with the regular xact.c code paths, must do this before * releasing locks, so do it before running the callbacks. * * NB: this code knows that we couldn't be dropping any temp rels ... */ if (isCommit) { for (i = 0; i < hdr->ncommitrels; i++) smgrdounlink(smgropen(commitrels[i]), false, false); } else { for (i = 0; i < hdr->nabortrels; i++) smgrdounlink(smgropen(abortrels[i]), false, false); } /* And now do the callbacks */ if (isCommit) ProcessRecords(bufptr, xid, twophase_postcommit_callbacks); else ProcessRecords(bufptr, xid, twophase_postabort_callbacks); /* Count the prepared xact as committed or aborted */ AtEOXact_PgStat(isCommit); /* * And now we can clean up our mess. */ RemoveTwoPhaseFile(xid, true); RemoveGXact(gxact); pfree(buf); } /* * Scan a 2PC state file (already read into memory by ReadTwoPhaseFile) * and call the indicated callbacks for each 2PC record. */ static void ProcessRecords(char *bufptr, TransactionId xid, const TwoPhaseCallback callbacks[]) { for (;;) { TwoPhaseRecordOnDisk *record = (TwoPhaseRecordOnDisk *) bufptr; Assert(record->rmid <= TWOPHASE_RM_MAX_ID); if (record->rmid == TWOPHASE_RM_END_ID) break; bufptr += MAXALIGN(sizeof(TwoPhaseRecordOnDisk)); if (callbacks[record->rmid] != NULL) callbacks[record->rmid] (xid, record->info, (void *) bufptr, record->len); bufptr += MAXALIGN(record->len); } } /* * Remove the 2PC file for the specified XID. * * If giveWarning is false, do not complain about file-not-present; * this is an expected case during WAL replay. */ void RemoveTwoPhaseFile(TransactionId xid, bool giveWarning) { char path[MAXPGPATH]; TwoPhaseFilePath(path, xid); if (unlink(path)) if (errno != ENOENT || giveWarning) ereport(WARNING, (errcode_for_file_access(), errmsg("could not remove two-phase state file \"%s\": %m", path))); } /* * Recreates a state file. This is used in WAL replay. * * Note: content and len don't include CRC. */ void RecreateTwoPhaseFile(TransactionId xid, void *content, int len) { char path[MAXPGPATH]; pg_crc32 statefile_crc; int fd; /* Recompute CRC */ INIT_CRC32(statefile_crc); COMP_CRC32(statefile_crc, content, len); FIN_CRC32(statefile_crc); TwoPhaseFilePath(path, xid); fd = BasicOpenFile(path, O_CREAT | O_TRUNC | O_WRONLY | PG_BINARY, S_IRUSR | S_IWUSR); if (fd < 0) ereport(ERROR, (errcode_for_file_access(), errmsg("could not recreate two-phase state file \"%s\": %m", path))); /* Write content and CRC */ if (write(fd, content, len) != len) { close(fd); ereport(ERROR, (errcode_for_file_access(), errmsg("could not write two-phase state file: %m"))); } if (write(fd, &statefile_crc, sizeof(pg_crc32)) != sizeof(pg_crc32)) { close(fd); ereport(ERROR, (errcode_for_file_access(), errmsg("could not write two-phase state file: %m"))); } /* * We must fsync the file because the end-of-replay checkpoint will not do * so, there being no GXACT in shared memory yet to tell it to. */ if (pg_fsync(fd) != 0) { close(fd); ereport(ERROR, (errcode_for_file_access(), errmsg("could not fsync two-phase state file: %m"))); } if (close(fd) != 0) ereport(ERROR, (errcode_for_file_access(), errmsg("could not close two-phase state file: %m"))); } /* * CheckPointTwoPhase -- handle 2PC component of checkpointing. * * We must fsync the state file of any GXACT that is valid and has a PREPARE * LSN <= the checkpoint's redo horizon. (If the gxact isn't valid yet or * has a later LSN, this checkpoint is not responsible for fsyncing it.) * * This is deliberately run as late as possible in the checkpoint sequence, * because GXACTs ordinarily have short lifespans, and so it is quite * possible that GXACTs that were valid at checkpoint start will no longer * exist if we wait a little bit. * * If a GXACT remains valid across multiple checkpoints, it'll be fsynced * each time. This is considered unusual enough that we don't bother to * expend any extra code to avoid the redundant fsyncs. (They should be * reasonably cheap anyway, since they won't cause I/O.) */ void CheckPointTwoPhase(XLogRecPtr redo_horizon) { TransactionId *xids; int nxids; char path[MAXPGPATH]; int i; /* * We don't want to hold the TwoPhaseStateLock while doing I/O, so we grab * it just long enough to make a list of the XIDs that require fsyncing, * and then do the I/O afterwards. * * This approach creates a race condition: someone else could delete a * GXACT between the time we release TwoPhaseStateLock and the time we try * to open its state file. We handle this by special-casing ENOENT * failures: if we see that, we verify that the GXACT is no longer valid, * and if so ignore the failure. */ if (max_prepared_xacts <= 0) return; /* nothing to do */ xids = (TransactionId *) palloc(max_prepared_xacts * sizeof(TransactionId)); nxids = 0; LWLockAcquire(TwoPhaseStateLock, LW_SHARED); for (i = 0; i < TwoPhaseState->numPrepXacts; i++) { GlobalTransaction gxact = TwoPhaseState->prepXacts[i]; if (gxact->valid && XLByteLE(gxact->prepare_lsn, redo_horizon)) xids[nxids++] = gxact->proc.xid; } LWLockRelease(TwoPhaseStateLock); for (i = 0; i < nxids; i++) { TransactionId xid = xids[i]; int fd; TwoPhaseFilePath(path, xid); fd = BasicOpenFile(path, O_RDWR | PG_BINARY, 0); if (fd < 0) { if (errno == ENOENT) { /* OK if gxact is no longer valid */ if (!TransactionIdIsPrepared(xid)) continue; /* Restore errno in case it was changed */ errno = ENOENT; } ereport(ERROR, (errcode_for_file_access(), errmsg("could not open two-phase state file \"%s\": %m", path))); } if (pg_fsync(fd) != 0) { close(fd); ereport(ERROR, (errcode_for_file_access(), errmsg("could not fsync two-phase state file \"%s\": %m", path))); } if (close(fd) != 0) ereport(ERROR, (errcode_for_file_access(), errmsg("could not close two-phase state file \"%s\": %m", path))); } pfree(xids); } /* * PrescanPreparedTransactions * * Scan the pg_twophase directory and determine the range of valid XIDs * present. This is run during database startup, after we have completed * reading WAL. ShmemVariableCache->nextXid has been set to one more than * the highest XID for which evidence exists in WAL. * * We throw away any prepared xacts with main XID beyond nextXid --- if any * are present, it suggests that the DBA has done a PITR recovery to an * earlier point in time without cleaning out pg_twophase. We dare not * try to recover such prepared xacts since they likely depend on database * state that doesn't exist now. * * However, we will advance nextXid beyond any subxact XIDs belonging to * valid prepared xacts. We need to do this since subxact commit doesn't * write a WAL entry, and so there might be no evidence in WAL of those * subxact XIDs. * * Our other responsibility is to determine and return the oldest valid XID * among the prepared xacts (if none, return ShmemVariableCache->nextXid). * This is needed to synchronize pg_subtrans startup properly. */ TransactionId PrescanPreparedTransactions(void) { TransactionId origNextXid = ShmemVariableCache->nextXid; TransactionId result = origNextXid; DIR *cldir; struct dirent *clde; cldir = AllocateDir(TWOPHASE_DIR); while ((clde = ReadDir(cldir, TWOPHASE_DIR)) != NULL) { if (strlen(clde->d_name) == 8 && strspn(clde->d_name, "0123456789ABCDEF") == 8) { TransactionId xid; char *buf; TwoPhaseFileHeader *hdr; TransactionId *subxids; int i; xid = (TransactionId) strtoul(clde->d_name, NULL, 16); /* Reject XID if too new */ if (TransactionIdFollowsOrEquals(xid, origNextXid)) { ereport(WARNING, (errmsg("removing future two-phase state file \"%s\"", clde->d_name))); RemoveTwoPhaseFile(xid, true); continue; } /* * Note: we can't check if already processed because clog * subsystem isn't up yet. */ /* Read and validate file */ buf = ReadTwoPhaseFile(xid); if (buf == NULL) { ereport(WARNING, (errmsg("removing corrupt two-phase state file \"%s\"", clde->d_name))); RemoveTwoPhaseFile(xid, true); continue; } /* Deconstruct header */ hdr = (TwoPhaseFileHeader *) buf; if (!TransactionIdEquals(hdr->xid, xid)) { ereport(WARNING, (errmsg("removing corrupt two-phase state file \"%s\"", clde->d_name))); RemoveTwoPhaseFile(xid, true); pfree(buf); continue; } /* * OK, we think this file is valid. Incorporate xid into the * running-minimum result. */ if (TransactionIdPrecedes(xid, result)) result = xid; /* * Examine subtransaction XIDs ... they should all follow main * XID, and they may force us to advance nextXid. */ subxids = (TransactionId *) (buf + MAXALIGN(sizeof(TwoPhaseFileHeader))); for (i = 0; i < hdr->nsubxacts; i++) { TransactionId subxid = subxids[i]; Assert(TransactionIdFollows(subxid, xid)); if (TransactionIdFollowsOrEquals(subxid, ShmemVariableCache->nextXid)) { ShmemVariableCache->nextXid = subxid; TransactionIdAdvance(ShmemVariableCache->nextXid); } } pfree(buf); } } FreeDir(cldir); return result; } /* * RecoverPreparedTransactions * * Scan the pg_twophase directory and reload shared-memory state for each * prepared transaction (reacquire locks, etc). This is run during database * startup. */ void RecoverPreparedTransactions(void) { char dir[MAXPGPATH]; DIR *cldir; struct dirent *clde; snprintf(dir, MAXPGPATH, "%s", TWOPHASE_DIR); cldir = AllocateDir(dir); while ((clde = ReadDir(cldir, dir)) != NULL) { if (strlen(clde->d_name) == 8 && strspn(clde->d_name, "0123456789ABCDEF") == 8) { TransactionId xid; char *buf; char *bufptr; TwoPhaseFileHeader *hdr; TransactionId *subxids; GlobalTransaction gxact; int i; xid = (TransactionId) strtoul(clde->d_name, NULL, 16); /* Already processed? */ if (TransactionIdDidCommit(xid) || TransactionIdDidAbort(xid)) { ereport(WARNING, (errmsg("removing stale two-phase state file \"%s\"", clde->d_name))); RemoveTwoPhaseFile(xid, true); continue; } /* Read and validate file */ buf = ReadTwoPhaseFile(xid); if (buf == NULL) { ereport(WARNING, (errmsg("removing corrupt two-phase state file \"%s\"", clde->d_name))); RemoveTwoPhaseFile(xid, true); continue; } ereport(LOG, (errmsg("recovering prepared transaction %u", xid))); /* Deconstruct header */ hdr = (TwoPhaseFileHeader *) buf; Assert(TransactionIdEquals(hdr->xid, xid)); bufptr = buf + MAXALIGN(sizeof(TwoPhaseFileHeader)); subxids = (TransactionId *) bufptr; bufptr += MAXALIGN(hdr->nsubxacts * sizeof(TransactionId)); bufptr += MAXALIGN(hdr->ncommitrels * sizeof(RelFileNode)); bufptr += MAXALIGN(hdr->nabortrels * sizeof(RelFileNode)); /* * Reconstruct subtrans state for the transaction --- needed * because pg_subtrans is not preserved over a restart. Note that * we are linking all the subtransactions directly to the * top-level XID; there may originally have been a more complex * hierarchy, but there's no need to restore that exactly. */ for (i = 0; i < hdr->nsubxacts; i++) SubTransSetParent(subxids[i], xid); /* * Recreate its GXACT and dummy PGPROC * * Note: since we don't have the PREPARE record's WAL location at * hand, we leave prepare_lsn zeroes. This means the GXACT will * be fsync'd on every future checkpoint. We assume this * situation is infrequent enough that the performance cost is * negligible (especially since we know the state file has already * been fsynced). */ gxact = MarkAsPreparing(xid, hdr->gid, hdr->prepared_at, hdr->owner, hdr->database); GXactLoadSubxactData(gxact, hdr->nsubxacts, subxids); MarkAsPrepared(gxact); /* * Recover other state (notably locks) using resource managers */ ProcessRecords(bufptr, xid, twophase_recover_callbacks); pfree(buf); } } FreeDir(cldir); } /* * RecordTransactionCommitPrepared * * This is basically the same as RecordTransactionCommit: in particular, * we must set the inCommit flag to avoid a race condition. * * We know the transaction made at least one XLOG entry (its PREPARE), * so it is never possible to optimize out the commit record. */ static void RecordTransactionCommitPrepared(TransactionId xid, int nchildren, TransactionId *children, int nrels, RelFileNode *rels) { XLogRecData rdata[3]; int lastrdata = 0; xl_xact_commit_prepared xlrec; XLogRecPtr recptr; START_CRIT_SECTION(); /* See notes in RecordTransactionCommit */ MyProc->inCommit = true; /* Emit the XLOG commit record */ xlrec.xid = xid; xlrec.crec.xact_time = GetCurrentTimestamp(); xlrec.crec.nrels = nrels; xlrec.crec.nsubxacts = nchildren; rdata[0].data = (char *) (&xlrec); rdata[0].len = MinSizeOfXactCommitPrepared; rdata[0].buffer = InvalidBuffer; /* dump rels to delete */ if (nrels > 0) { rdata[0].next = &(rdata[1]); rdata[1].data = (char *) rels; rdata[1].len = nrels * sizeof(RelFileNode); rdata[1].buffer = InvalidBuffer; lastrdata = 1; } /* dump committed child Xids */ if (nchildren > 0) { rdata[lastrdata].next = &(rdata[2]); rdata[2].data = (char *) children; rdata[2].len = nchildren * sizeof(TransactionId); rdata[2].buffer = InvalidBuffer; lastrdata = 2; } rdata[lastrdata].next = NULL; recptr = XLogInsert(RM_XACT_ID, XLOG_XACT_COMMIT_PREPARED, rdata); /* * We don't currently try to sleep before flush here ... nor is there any * support for async commit of a prepared xact (the very idea is probably * a contradiction) */ /* Flush XLOG to disk */ XLogFlush(recptr); /* Mark the transaction committed in pg_clog */ TransactionIdCommit(xid); /* to avoid race conditions, the parent must commit first */ TransactionIdCommitTree(nchildren, children); /* Checkpoint can proceed now */ MyProc->inCommit = false; END_CRIT_SECTION(); } /* * RecordTransactionAbortPrepared * * This is basically the same as RecordTransactionAbort. * * We know the transaction made at least one XLOG entry (its PREPARE), * so it is never possible to optimize out the abort record. */ static void RecordTransactionAbortPrepared(TransactionId xid, int nchildren, TransactionId *children, int nrels, RelFileNode *rels) { XLogRecData rdata[3]; int lastrdata = 0; xl_xact_abort_prepared xlrec; XLogRecPtr recptr; /* * Catch the scenario where we aborted partway through * RecordTransactionCommitPrepared ... */ if (TransactionIdDidCommit(xid)) elog(PANIC, "cannot abort transaction %u, it was already committed", xid); START_CRIT_SECTION(); /* Emit the XLOG abort record */ xlrec.xid = xid; xlrec.arec.xact_time = GetCurrentTimestamp(); xlrec.arec.nrels = nrels; xlrec.arec.nsubxacts = nchildren; rdata[0].data = (char *) (&xlrec); rdata[0].len = MinSizeOfXactAbortPrepared; rdata[0].buffer = InvalidBuffer; /* dump rels to delete */ if (nrels > 0) { rdata[0].next = &(rdata[1]); rdata[1].data = (char *) rels; rdata[1].len = nrels * sizeof(RelFileNode); rdata[1].buffer = InvalidBuffer; lastrdata = 1; } /* dump committed child Xids */ if (nchildren > 0) { rdata[lastrdata].next = &(rdata[2]); rdata[2].data = (char *) children; rdata[2].len = nchildren * sizeof(TransactionId); rdata[2].buffer = InvalidBuffer; lastrdata = 2; } rdata[lastrdata].next = NULL; recptr = XLogInsert(RM_XACT_ID, XLOG_XACT_ABORT_PREPARED, rdata); /* Always flush, since we're about to remove the 2PC state file */ XLogFlush(recptr); /* * Mark the transaction aborted in clog. This is not absolutely necessary * but we may as well do it while we are here. */ TransactionIdAbort(xid); TransactionIdAbortTree(nchildren, children); END_CRIT_SECTION(); }