diff options
Diffstat (limited to 'src/backend/access/transam/twophase.c')
| -rw-r--r-- | src/backend/access/transam/twophase.c | 2456 |
1 files changed, 2456 insertions, 0 deletions
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c new file mode 100644 index 0000000..e0a4b2a --- /dev/null +++ b/src/backend/access/transam/twophase.c @@ -0,0 +1,2456 @@ +/*------------------------------------------------------------------------- + * + * twophase.c + * Two-phase commit support functions. + * + * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group + * Portions Copyright (c) 1994, Regents of the University of California + * + * IDENTIFICATION + * src/backend/access/transam/twophase.c + * + * 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 dummy PGXACT and PGPROC; this is + * what keeps the XID considered running by TransactionIdIsInProgress. + * It is also convenient as a PGPROC to hook the gxact's locks to. + * + * Information to recover prepared transactions in case of crash is + * now stored in WAL for the common case. In some cases there will be + * an extended period between preparing a GXACT and commit/abort, in + * which case we need to separately record prepared transaction data + * 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. + * All prepared transactions will be written prior to shutdown. + * + * Life track of state data is following: + * + * * On PREPARE TRANSACTION backend writes state data only to the WAL and + * stores pointer to the start of the WAL record in + * gxact->prepare_start_lsn. + * * If COMMIT occurs before checkpoint then backend reads data from WAL + * using prepare_start_lsn. + * * On checkpoint state data copied to files in pg_twophase directory and + * fsynced + * * If COMMIT happens after checkpoint then backend reads state data from + * files + * + * During replay and replication, TwoPhaseState also holds information + * about active prepared transactions that haven't been moved to disk yet. + * + * Replay of twophase records happens by the following rules: + * + * * At the beginning of recovery, pg_twophase is scanned once, filling + * TwoPhaseState with entries marked with gxact->inredo and + * gxact->ondisk. Two-phase file data older than the XID horizon of + * the redo position are discarded. + * * On PREPARE redo, the transaction is added to TwoPhaseState->prepXacts. + * gxact->inredo is set to true for such entries. + * * On Checkpoint we iterate through TwoPhaseState->prepXacts entries + * that have gxact->inredo set and are behind the redo_horizon. We + * save them to disk and then switch gxact->ondisk to true. + * * On COMMIT/ABORT we delete the entry from TwoPhaseState->prepXacts. + * If gxact->ondisk is true, the corresponding entry from the disk + * is additionally deleted. + * * RecoverPreparedTransactions(), StandbyRecoverPreparedTransactions() + * and PrescanPreparedTransactions() have been modified to go through + * gxact->inredo entries that have not made it to disk. + * + *------------------------------------------------------------------------- + */ +#include "postgres.h" + +#include <fcntl.h> +#include <sys/stat.h> +#include <time.h> +#include <unistd.h> + +#include "access/commit_ts.h" +#include "access/htup_details.h" +#include "access/subtrans.h" +#include "access/transam.h" +#include "access/twophase.h" +#include "access/twophase_rmgr.h" +#include "access/xact.h" +#include "access/xlog.h" +#include "access/xloginsert.h" +#include "access/xlogreader.h" +#include "access/xlogutils.h" +#include "catalog/pg_type.h" +#include "catalog/storage.h" +#include "funcapi.h" +#include "miscadmin.h" +#include "pg_trace.h" +#include "pgstat.h" +#include "replication/origin.h" +#include "replication/syncrep.h" +#include "replication/walsender.h" +#include "storage/fd.h" +#include "storage/ipc.h" +#include "storage/md.h" +#include "storage/predicate.h" +#include "storage/proc.h" +#include "storage/procarray.h" +#include "storage/sinvaladt.h" +#include "storage/smgr.h" +#include "utils/builtins.h" +#include "utils/memutils.h" +#include "utils/timestamp.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 = 0; + +/* + * This struct describes one global transaction that is in prepared state + * or attempting to become prepared. + * + * 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 GID and valid = false, + * and mark it as locked by my backend. + * + * 2. After successfully completing prepare, set valid = true and enter the + * referenced PGPROC into the global ProcArray. + * + * 3. To begin COMMIT PREPARED or ROLLBACK PREPARED, check that the entry is + * valid and not locked, then mark the entry as locked by storing my current + * backend ID into locking_backend. 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 must be removed so that the GID and the GlobalTransaction struct + * can be reused. See AtAbort_Twophase(). + * + * typedef struct GlobalTransactionData *GlobalTransaction appears in + * twophase.h + */ + +typedef struct GlobalTransactionData +{ + GlobalTransaction next; /* list link for free list */ + int pgprocno; /* ID of associated dummy PGPROC */ + BackendId dummyBackendId; /* similar to backend id for backends */ + TimestampTz prepared_at; /* time of preparation */ + + /* + * Note that we need to keep track of two LSNs for each GXACT. We keep + * track of the start LSN because this is the address we must use to read + * state data back from WAL when committing a prepared GXACT. We keep + * track of the end LSN because that is the LSN we need to wait for prior + * to commit. + */ + XLogRecPtr prepare_start_lsn; /* XLOG offset of prepare record start */ + XLogRecPtr prepare_end_lsn; /* XLOG offset of prepare record end */ + TransactionId xid; /* The GXACT id */ + + Oid owner; /* ID of user that executed the xact */ + BackendId locking_backend; /* backend currently working on the xact */ + bool valid; /* true if PGPROC entry is in proc array */ + bool ondisk; /* true if prepare state file is on disk */ + bool inredo; /* true if entry was added via xlog_redo */ + 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 */ + GlobalTransaction freeGXacts; + + /* Number of valid prepXacts entries. */ + int numPrepXacts; + + /* There are max_prepared_xacts items in this array */ + GlobalTransaction prepXacts[FLEXIBLE_ARRAY_MEMBER]; +} TwoPhaseStateData; + +static TwoPhaseStateData *TwoPhaseState; + +/* + * Global transaction entry currently locked by us, if any. Note that any + * access to the entry pointed to by this variable must be protected by + * TwoPhaseStateLock, though obviously the pointer itself doesn't need to be + * (since it's just local memory). + */ +static GlobalTransaction MyLockedGxact = NULL; + +static bool twophaseExitRegistered = false; + +static void RecordTransactionCommitPrepared(TransactionId xid, + int nchildren, + TransactionId *children, + int nrels, + RelFileNode *rels, + int ninvalmsgs, + SharedInvalidationMessage *invalmsgs, + bool initfileinval, + const char *gid); +static void RecordTransactionAbortPrepared(TransactionId xid, + int nchildren, + TransactionId *children, + int nrels, + RelFileNode *rels, + const char *gid); +static void ProcessRecords(char *bufptr, TransactionId xid, + const TwoPhaseCallback callbacks[]); +static void RemoveGXact(GlobalTransaction gxact); + +static void XlogReadTwoPhaseData(XLogRecPtr lsn, char **buf, int *len); +static char *ProcessTwoPhaseBuffer(TransactionId xid, + XLogRecPtr prepare_start_lsn, + bool fromdisk, bool setParent, bool setNextXid); +static void MarkAsPreparingGuts(GlobalTransaction gxact, TransactionId xid, + const char *gid, TimestampTz prepared_at, Oid owner, + Oid databaseid); +static void RemoveTwoPhaseFile(TransactionId xid, bool giveWarning); +static void RecreateTwoPhaseFile(TransactionId xid, void *content, int len); + +/* + * 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 = NULL; + 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++) + { + /* insert into linked list */ + gxacts[i].next = TwoPhaseState->freeGXacts; + TwoPhaseState->freeGXacts = &gxacts[i]; + + /* associate it with a PGPROC assigned by InitProcGlobal */ + gxacts[i].pgprocno = PreparedXactProcs[i].pgprocno; + + /* + * Assign a unique ID for each dummy proc, so that the range of + * dummy backend IDs immediately follows the range of normal + * backend IDs. We don't dare to assign a real backend ID to dummy + * procs, because prepared transactions don't take part in cache + * invalidation like a real backend ID would imply, but having a + * unique ID for them is nevertheless handy. This arrangement + * allows you to allocate an array of size (MaxBackends + + * max_prepared_xacts + 1), and have a slot for every backend and + * prepared transaction. Currently multixact.c uses that + * technique. + */ + gxacts[i].dummyBackendId = MaxBackends + 1 + i; + } + } + else + Assert(found); +} + +/* + * Exit hook to unlock the global transaction entry we're working on. + */ +static void +AtProcExit_Twophase(int code, Datum arg) +{ + /* same logic as abort */ + AtAbort_Twophase(); +} + +/* + * Abort hook to unlock the global transaction entry we're working on. + */ +void +AtAbort_Twophase(void) +{ + if (MyLockedGxact == NULL) + return; + + /* + * What to do with the locked global transaction entry? If we were in the + * process of preparing the transaction, but haven't written the WAL + * record and state file yet, the transaction must not be considered as + * prepared. Likewise, if we are in the process of finishing an + * already-prepared transaction, and fail after having already written the + * 2nd phase commit or rollback record to the WAL, the transaction should + * not be considered as prepared anymore. In those cases, just remove the + * entry from shared memory. + * + * Otherwise, the entry must be left in place so that the transaction can + * be finished later, so just unlock it. + * + * If we abort during prepare, after having written the WAL record, we + * might not have transferred all locks and other state to the prepared + * transaction yet. Likewise, if we abort during commit or rollback, + * after having written the WAL record, we might not have released all the + * resources held by the transaction yet. In those cases, the in-memory + * state can be wrong, but it's too late to back out. + */ + LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE); + if (!MyLockedGxact->valid) + RemoveGXact(MyLockedGxact); + else + MyLockedGxact->locking_backend = InvalidBackendId; + LWLockRelease(TwoPhaseStateLock); + + MyLockedGxact = NULL; +} + +/* + * This is called after we have finished transferring state to the prepared + * PGXACT entry. + */ +void +PostPrepare_Twophase(void) +{ + LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE); + MyLockedGxact->locking_backend = InvalidBackendId; + LWLockRelease(TwoPhaseStateLock); + + MyLockedGxact = NULL; +} + + +/* + * MarkAsPreparing + * Reserve the GID for the given transaction. + */ +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))); + + /* fail immediately if feature is disabled */ + if (max_prepared_xacts == 0) + ereport(ERROR, + (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE), + errmsg("prepared transactions are disabled"), + errhint("Set max_prepared_transactions to a nonzero value."))); + + /* on first call, register the exit hook */ + if (!twophaseExitRegistered) + { + before_shmem_exit(AtProcExit_Twophase, 0); + twophaseExitRegistered = true; + } + + LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE); + + /* 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 == NULL) + 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 = TwoPhaseState->freeGXacts; + TwoPhaseState->freeGXacts = gxact->next; + + MarkAsPreparingGuts(gxact, xid, gid, prepared_at, owner, databaseid); + + gxact->ondisk = false; + + /* And insert it into the active array */ + Assert(TwoPhaseState->numPrepXacts < max_prepared_xacts); + TwoPhaseState->prepXacts[TwoPhaseState->numPrepXacts++] = gxact; + + LWLockRelease(TwoPhaseStateLock); + + return gxact; +} + +/* + * MarkAsPreparingGuts + * + * This uses 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. + * + * Note: This function should be called with appropriate locks held. + */ +static void +MarkAsPreparingGuts(GlobalTransaction gxact, TransactionId xid, const char *gid, + TimestampTz prepared_at, Oid owner, Oid databaseid) +{ + PGPROC *proc; + PGXACT *pgxact; + int i; + + Assert(LWLockHeldByMeInMode(TwoPhaseStateLock, LW_EXCLUSIVE)); + + Assert(gxact != NULL); + proc = &ProcGlobal->allProcs[gxact->pgprocno]; + pgxact = &ProcGlobal->allPgXact[gxact->pgprocno]; + + /* Initialize the PGPROC entry */ + MemSet(proc, 0, sizeof(PGPROC)); + proc->pgprocno = gxact->pgprocno; + SHMQueueElemInit(&(proc->links)); + proc->waitStatus = STATUS_OK; + /* We set up the gxact's VXID as InvalidBackendId/XID */ + proc->lxid = (LocalTransactionId) xid; + pgxact->xid = xid; + pgxact->xmin = InvalidTransactionId; + proc->delayChkpt = false; + pgxact->vacuumFlags = 0; + proc->pid = 0; + proc->backendId = InvalidBackendId; + proc->databaseId = databaseid; + proc->roleId = owner; + proc->tempNamespaceId = InvalidOid; + proc->isBackgroundWorker = false; + proc->lwWaiting = false; + proc->lwWaitMode = 0; + proc->waitLock = NULL; + proc->waitProcLock = NULL; + for (i = 0; i < NUM_LOCK_PARTITIONS; i++) + SHMQueueInit(&(proc->myProcLocks[i])); + /* subxid data must be filled later by GXactLoadSubxactData */ + pgxact->overflowed = false; + pgxact->nxids = 0; + + gxact->prepared_at = prepared_at; + gxact->xid = xid; + gxact->owner = owner; + gxact->locking_backend = MyBackendId; + gxact->valid = false; + gxact->inredo = false; + strcpy(gxact->gid, gid); + + /* + * Remember that we have this GlobalTransaction entry locked for us. If we + * abort after this, we must release it. + */ + MyLockedGxact = 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) +{ + PGPROC *proc = &ProcGlobal->allProcs[gxact->pgprocno]; + PGXACT *pgxact = &ProcGlobal->allPgXact[gxact->pgprocno]; + + /* We need no extra lock since the GXACT isn't valid yet */ + if (nsubxacts > PGPROC_MAX_CACHED_SUBXIDS) + { + pgxact->overflowed = true; + nsubxacts = PGPROC_MAX_CACHED_SUBXIDS; + } + if (nsubxacts > 0) + { + memcpy(proc->subxids.xids, children, + nsubxacts * sizeof(TransactionId)); + pgxact->nxids = nsubxacts; + } +} + +/* + * MarkAsPrepared + * Mark the GXACT as fully valid, and enter it into the global ProcArray. + * + * lock_held indicates whether caller already holds TwoPhaseStateLock. + */ +static void +MarkAsPrepared(GlobalTransaction gxact, bool lock_held) +{ + /* Lock here may be overkill, but I'm not convinced of that ... */ + if (!lock_held) + LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE); + Assert(!gxact->valid); + gxact->valid = true; + if (!lock_held) + LWLockRelease(TwoPhaseStateLock); + + /* + * Put it into the global ProcArray so TransactionIdIsInProgress considers + * the XID as still running. + */ + ProcArrayAdd(&ProcGlobal->allProcs[gxact->pgprocno]); +} + +/* + * LockGXact + * Locate the prepared transaction and mark it busy for COMMIT or PREPARE. + */ +static GlobalTransaction +LockGXact(const char *gid, Oid user) +{ + int i; + + /* on first call, register the exit hook */ + if (!twophaseExitRegistered) + { + before_shmem_exit(AtProcExit_Twophase, 0); + twophaseExitRegistered = true; + } + + LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE); + + for (i = 0; i < TwoPhaseState->numPrepXacts; i++) + { + GlobalTransaction gxact = TwoPhaseState->prepXacts[i]; + PGPROC *proc = &ProcGlobal->allProcs[gxact->pgprocno]; + + /* 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 (gxact->locking_backend != InvalidBackendId) + ereport(ERROR, + (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE), + errmsg("prepared transaction with identifier \"%s\" is busy", + gid))); + + 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 != 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_backend = MyBackendId; + MyLockedGxact = gxact; + + 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; + + Assert(LWLockHeldByMeInMode(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->next = TwoPhaseState->freeGXacts; + TwoPhaseState->freeGXacts = gxact; + + return; + } + } + + elog(ERROR, "failed to find %p in GlobalTransaction array", gxact); +} + +/* + * 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); + 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++]; + PGPROC *proc = &ProcGlobal->allProcs[gxact->pgprocno]; + PGXACT *pgxact = &ProcGlobal->allPgXact[gxact->pgprocno]; + 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(pgxact->xid); + values[1] = CStringGetTextDatum(gxact->gid); + values[2] = TimestampTzGetDatum(gxact->prepared_at); + values[3] = ObjectIdGetDatum(gxact->owner); + values[4] = ObjectIdGetDatum(proc->databaseId); + + tuple = heap_form_tuple(funcctx->tuple_desc, values, nulls); + result = HeapTupleGetDatum(tuple); + SRF_RETURN_NEXT(funcctx, result); + } + + SRF_RETURN_DONE(funcctx); +} + +/* + * TwoPhaseGetGXact + * Get the GlobalTransaction struct for a prepared transaction + * specified by XID + * + * If lock_held is set to true, TwoPhaseStateLock will not be taken, so the + * caller had better hold it. + */ +static GlobalTransaction +TwoPhaseGetGXact(TransactionId xid, bool lock_held) +{ + GlobalTransaction result = NULL; + int i; + + static TransactionId cached_xid = InvalidTransactionId; + static GlobalTransaction cached_gxact = NULL; + + Assert(!lock_held || LWLockHeldByMe(TwoPhaseStateLock)); + + /* + * 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_gxact; + + if (!lock_held) + LWLockAcquire(TwoPhaseStateLock, LW_SHARED); + + for (i = 0; i < TwoPhaseState->numPrepXacts; i++) + { + GlobalTransaction gxact = TwoPhaseState->prepXacts[i]; + PGXACT *pgxact = &ProcGlobal->allPgXact[gxact->pgprocno]; + + if (pgxact->xid == xid) + { + result = gxact; + break; + } + } + + if (!lock_held) + LWLockRelease(TwoPhaseStateLock); + + if (result == NULL) /* should not happen */ + elog(ERROR, "failed to find GlobalTransaction for xid %u", xid); + + cached_xid = xid; + cached_gxact = result; + + return result; +} + +/* + * TwoPhaseGetDummyBackendId + * Get the dummy backend ID for prepared transaction specified by XID + * + * Dummy backend IDs are similar to real backend IDs of real backends. + * They start at MaxBackends + 1, and are unique across all currently active + * real backends and prepared transactions. If lock_held is set to true, + * TwoPhaseStateLock will not be taken, so the caller had better hold it. + */ +BackendId +TwoPhaseGetDummyBackendId(TransactionId xid, bool lock_held) +{ + GlobalTransaction gxact = TwoPhaseGetGXact(xid, lock_held); + + return gxact->dummyBackendId; +} + +/* + * TwoPhaseGetDummyProc + * Get the PGPROC that represents a prepared transaction specified by XID + * + * If lock_held is set to true, TwoPhaseStateLock will not be taken, so the + * caller had better hold it. + */ +PGPROC * +TwoPhaseGetDummyProc(TransactionId xid, bool lock_held) +{ + GlobalTransaction gxact = TwoPhaseGetGXact(xid, lock_held); + + return &ProcGlobal->allProcs[gxact->pgprocno]; +} + +/************************************************************************/ +/* 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. SharedInvalidationMessage[] (inval messages to be sent at commit) + * 6. TwoPhaseRecordOnDisk + * 7. ... + * 8. TwoPhaseRecordOnDisk (end sentinel, rmid == TWOPHASE_RM_END_ID) + * 9. checksum (CRC-32C) + * + * Each segment except the final checksum is MAXALIGN'd. + */ + +/* + * Header for a 2PC state file + */ +#define TWOPHASE_MAGIC 0x57F94534 /* format identifier */ + +typedef xl_xact_prepare 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 StateFileChunk blocks + * for that. + */ +typedef struct StateFileChunk +{ + char *data; + uint32 len; + struct StateFileChunk *next; +} StateFileChunk; + +static struct xllist +{ + StateFileChunk *head; /* first data block in the chain */ + StateFileChunk *tail; /* last block in chain */ + uint32 num_chunks; + 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(StateFileChunk)); + records.tail = records.tail->next; + records.tail->len = 0; + records.tail->next = NULL; + records.num_chunks++; + + 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) +{ + PGPROC *proc = &ProcGlobal->allProcs[gxact->pgprocno]; + PGXACT *pgxact = &ProcGlobal->allPgXact[gxact->pgprocno]; + TransactionId xid = pgxact->xid; + TwoPhaseFileHeader hdr; + TransactionId *children; + RelFileNode *commitrels; + RelFileNode *abortrels; + SharedInvalidationMessage *invalmsgs; + + /* Initialize linked list */ + records.head = palloc0(sizeof(StateFileChunk)); + 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.num_chunks = 1; + + records.total_len = 0; + + /* Create header */ + hdr.magic = TWOPHASE_MAGIC; + hdr.total_len = 0; /* EndPrepare will fill this in */ + hdr.xid = xid; + hdr.database = proc->databaseId; + hdr.prepared_at = gxact->prepared_at; + hdr.owner = gxact->owner; + hdr.nsubxacts = xactGetCommittedChildren(&children); + hdr.ncommitrels = smgrGetPendingDeletes(true, &commitrels); + hdr.nabortrels = smgrGetPendingDeletes(false, &abortrels); + hdr.ninvalmsgs = xactGetCommittedInvalidationMessages(&invalmsgs, + &hdr.initfileinval); + hdr.gidlen = strlen(gxact->gid) + 1; /* Include '\0' */ + + save_state_data(&hdr, sizeof(TwoPhaseFileHeader)); + save_state_data(gxact->gid, hdr.gidlen); + + /* + * Add the additional info about subxacts, deletable files and cache + * invalidation messages. + */ + 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); + } + if (hdr.ninvalmsgs > 0) + { + save_state_data(invalmsgs, + hdr.ninvalmsgs * sizeof(SharedInvalidationMessage)); + pfree(invalmsgs); + } +} + +/* + * Finish preparing state data and writing it to WAL. + */ +void +EndPrepare(GlobalTransaction gxact) +{ + TwoPhaseFileHeader *hdr; + StateFileChunk *record; + bool replorigin; + + /* 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_crc32c); + + replorigin = (replorigin_session_origin != InvalidRepOriginId && + replorigin_session_origin != DoNotReplicateId); + + if (replorigin) + { + Assert(replorigin_session_origin_lsn != InvalidXLogRecPtr); + hdr->origin_lsn = replorigin_session_origin_lsn; + hdr->origin_timestamp = replorigin_session_origin_timestamp; + } + else + { + hdr->origin_lsn = InvalidXLogRecPtr; + hdr->origin_timestamp = 0; + } + + /* + * If the data size exceeds MaxAllocSize, we won't be able to read it in + * ReadTwoPhaseFile. Check for that now, rather than fail in the case + * where we write data to file and then re-read at commit time. + */ + if (hdr->total_len > MaxAllocSize) + ereport(ERROR, + (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED), + errmsg("two-phase state file maximum length exceeded"))); + + /* + * Now writing 2PC state data to WAL. We let the WAL's CRC protection + * cover us, so no need to calculate a separate CRC. + * + * We have to set delayChkpt 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 delayChkpt for; see notes there.) + * + * We save the PREPARE record's location in the gxact for later use by + * CheckPointTwoPhase. + */ + XLogEnsureRecordSpace(0, records.num_chunks); + + START_CRIT_SECTION(); + + MyProc->delayChkpt = true; + + XLogBeginInsert(); + for (record = records.head; record != NULL; record = record->next) + XLogRegisterData(record->data, record->len); + + XLogSetRecordFlags(XLOG_INCLUDE_ORIGIN); + + gxact->prepare_end_lsn = XLogInsert(RM_XACT_ID, XLOG_XACT_PREPARE); + + if (replorigin) + { + /* Move LSNs forward for this replication origin */ + replorigin_session_advance(replorigin_session_origin_lsn, + gxact->prepare_end_lsn); + } + + XLogFlush(gxact->prepare_end_lsn); + + /* If we crash now, we have prepared: WAL replay will fix things */ + + /* Store record's start location to read that later on Commit */ + gxact->prepare_start_lsn = ProcLastRecPtr; + + /* + * Mark the prepared transaction as valid. As soon as xact.c marks + * MyPgXact 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 MyPgXact, + * 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, false); + + /* + * 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->delayChkpt = false; + + /* + * Remember that we have this GlobalTransaction entry locked for us. If + * we crash after this point, it's too late to abort, but we must unlock + * it so that the prepared transaction can be committed or rolled back. + */ + MyLockedGxact = gxact; + + END_CRIT_SECTION(); + + /* + * Wait for synchronous replication, if required. + * + * Note that at this stage we have marked the prepare, but still show as + * running in the procarray (twice!) and continue to hold locks. + */ + SyncRepWaitForLSN(gxact->prepare_end_lsn, false); + + records.tail = records.head = NULL; + records.num_chunks = 0; +} + +/* + * 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, issuing an error when finding corrupted data. If + * missing_ok is true, which indicates that missing files can be safely + * ignored, then return NULL. This state can be reached when doing recovery. + */ +static char * +ReadTwoPhaseFile(TransactionId xid, bool missing_ok) +{ + char path[MAXPGPATH]; + char *buf; + TwoPhaseFileHeader *hdr; + int fd; + struct stat stat; + uint32 crc_offset; + pg_crc32c calc_crc, + file_crc; + int r; + + TwoPhaseFilePath(path, xid); + + fd = OpenTransientFile(path, O_RDONLY | PG_BINARY); + if (fd < 0) + { + if (missing_ok && errno == ENOENT) + return NULL; + + ereport(ERROR, + (errcode_for_file_access(), + errmsg("could not open file \"%s\": %m", path))); + } + + /* + * Check file length. We can determine a lower bound pretty easily. We + * set an upper bound to avoid palloc() failure on a corrupt file, though + * we can't guarantee that we won't get an out of memory error anyway, + * even on a valid file. + */ + if (fstat(fd, &stat)) + ereport(ERROR, + (errcode_for_file_access(), + errmsg("could not stat file \"%s\": %m", path))); + + if (stat.st_size < (MAXALIGN(sizeof(TwoPhaseFileHeader)) + + MAXALIGN(sizeof(TwoPhaseRecordOnDisk)) + + sizeof(pg_crc32c)) || + stat.st_size > MaxAllocSize) + ereport(ERROR, + (errcode(ERRCODE_DATA_CORRUPTED), + errmsg_plural("incorrect size of file \"%s\": %zu byte", + "incorrect size of file \"%s\": %zu bytes", + (Size) stat.st_size, path, + (Size) stat.st_size))); + + crc_offset = stat.st_size - sizeof(pg_crc32c); + if (crc_offset != MAXALIGN(crc_offset)) + ereport(ERROR, + (errcode(ERRCODE_DATA_CORRUPTED), + errmsg("incorrect alignment of CRC offset for file \"%s\"", + path))); + + /* + * OK, slurp in the file. + */ + buf = (char *) palloc(stat.st_size); + + pgstat_report_wait_start(WAIT_EVENT_TWOPHASE_FILE_READ); + r = read(fd, buf, stat.st_size); + if (r != stat.st_size) + { + if (r < 0) + ereport(ERROR, + (errcode_for_file_access(), + errmsg("could not read file \"%s\": %m", path))); + else + ereport(ERROR, + (errmsg("could not read file \"%s\": read %d of %zu", + path, r, (Size) stat.st_size))); + } + + pgstat_report_wait_end(); + + if (CloseTransientFile(fd) != 0) + ereport(ERROR, + (errcode_for_file_access(), + errmsg("could not close file \"%s\": %m", path))); + + hdr = (TwoPhaseFileHeader *) buf; + if (hdr->magic != TWOPHASE_MAGIC) + ereport(ERROR, + (errcode(ERRCODE_DATA_CORRUPTED), + errmsg("invalid magic number stored in file \"%s\"", + path))); + + if (hdr->total_len != stat.st_size) + ereport(ERROR, + (errcode(ERRCODE_DATA_CORRUPTED), + errmsg("invalid size stored in file \"%s\"", + path))); + + INIT_CRC32C(calc_crc); + COMP_CRC32C(calc_crc, buf, crc_offset); + FIN_CRC32C(calc_crc); + + file_crc = *((pg_crc32c *) (buf + crc_offset)); + + if (!EQ_CRC32C(calc_crc, file_crc)) + ereport(ERROR, + (errcode(ERRCODE_DATA_CORRUPTED), + errmsg("calculated CRC checksum does not match value stored in file \"%s\"", + path))); + + return buf; +} + + +/* + * Reads 2PC data from xlog. During checkpoint this data will be moved to + * twophase files and ReadTwoPhaseFile should be used instead. + * + * Note clearly that this function can access WAL during normal operation, + * similarly to the way WALSender or Logical Decoding would do. While + * accessing WAL, read_local_xlog_page() may change ThisTimeLineID, + * particularly if this routine is called for the end-of-recovery checkpoint + * in the checkpointer itself, so save the current timeline number value + * and restore it once done. + */ +static void +XlogReadTwoPhaseData(XLogRecPtr lsn, char **buf, int *len) +{ + XLogRecord *record; + XLogReaderState *xlogreader; + char *errormsg; + TimeLineID save_currtli = ThisTimeLineID; + + xlogreader = XLogReaderAllocate(wal_segment_size, NULL, + XL_ROUTINE(.page_read = &read_local_xlog_page, + .segment_open = &wal_segment_open, + .segment_close = &wal_segment_close), + NULL); + if (!xlogreader) + ereport(ERROR, + (errcode(ERRCODE_OUT_OF_MEMORY), + errmsg("out of memory"), + errdetail("Failed while allocating a WAL reading processor."))); + + XLogBeginRead(xlogreader, lsn); + record = XLogReadRecord(xlogreader, &errormsg); + + /* + * Restore immediately the timeline where it was previously, as + * read_local_xlog_page() could have changed it if the record was read + * while recovery was finishing or if the timeline has jumped in-between. + */ + ThisTimeLineID = save_currtli; + + if (record == NULL) + ereport(ERROR, + (errcode_for_file_access(), + errmsg("could not read two-phase state from WAL at %X/%X", + (uint32) (lsn >> 32), + (uint32) lsn))); + + if (XLogRecGetRmid(xlogreader) != RM_XACT_ID || + (XLogRecGetInfo(xlogreader) & XLOG_XACT_OPMASK) != XLOG_XACT_PREPARE) + ereport(ERROR, + (errcode_for_file_access(), + errmsg("expected two-phase state data is not present in WAL at %X/%X", + (uint32) (lsn >> 32), + (uint32) lsn))); + + if (len != NULL) + *len = XLogRecGetDataLen(xlogreader); + + *buf = palloc(sizeof(char) * XLogRecGetDataLen(xlogreader)); + memcpy(*buf, XLogRecGetData(xlogreader), sizeof(char) * XLogRecGetDataLen(xlogreader)); + + XLogReaderFree(xlogreader); +} + + +/* + * Confirms an xid is prepared, during recovery + */ +bool +StandbyTransactionIdIsPrepared(TransactionId xid) +{ + char *buf; + TwoPhaseFileHeader *hdr; + bool result; + + Assert(TransactionIdIsValid(xid)); + + if (max_prepared_xacts <= 0) + return false; /* nothing to do */ + + /* Read and validate file */ + buf = ReadTwoPhaseFile(xid, true); + if (buf == NULL) + return false; + + /* Check header also */ + hdr = (TwoPhaseFileHeader *) buf; + result = TransactionIdEquals(hdr->xid, xid); + pfree(buf); + + return result; +} + +/* + * FinishPreparedTransaction: execute COMMIT PREPARED or ROLLBACK PREPARED + */ +void +FinishPreparedTransaction(const char *gid, bool isCommit) +{ + GlobalTransaction gxact; + PGPROC *proc; + PGXACT *pgxact; + TransactionId xid; + char *buf; + char *bufptr; + TwoPhaseFileHeader *hdr; + TransactionId latestXid; + TransactionId *children; + RelFileNode *commitrels; + RelFileNode *abortrels; + RelFileNode *delrels; + int ndelrels; + SharedInvalidationMessage *invalmsgs; + + /* + * 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()); + proc = &ProcGlobal->allProcs[gxact->pgprocno]; + pgxact = &ProcGlobal->allPgXact[gxact->pgprocno]; + xid = pgxact->xid; + + /* + * Read and validate 2PC state data. State data will typically be stored + * in WAL files if the LSN is after the last checkpoint record, or moved + * to disk if for some reason they have lived for a long time. + */ + if (gxact->ondisk) + buf = ReadTwoPhaseFile(xid, false); + else + XlogReadTwoPhaseData(gxact->prepare_start_lsn, &buf, NULL); + + + /* + * Disassemble the header area + */ + hdr = (TwoPhaseFileHeader *) buf; + Assert(TransactionIdEquals(hdr->xid, xid)); + bufptr = buf + MAXALIGN(sizeof(TwoPhaseFileHeader)); + bufptr += MAXALIGN(hdr->gidlen); + 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)); + invalmsgs = (SharedInvalidationMessage *) bufptr; + bufptr += MAXALIGN(hdr->ninvalmsgs * sizeof(SharedInvalidationMessage)); + + /* compute latestXid among all children */ + latestXid = TransactionIdLatest(xid, hdr->nsubxacts, children); + + /* Prevent cancel/die interrupt while cleaning up */ + HOLD_INTERRUPTS(); + + /* + * The order of operations here is critical: make the XLOG entry for + * commit or abort, then mark the transaction committed or aborted in + * pg_xact, 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, + hdr->ninvalmsgs, invalmsgs, + hdr->initfileinval, gid); + else + RecordTransactionAbortPrepared(xid, + hdr->nsubxacts, children, + hdr->nabortrels, abortrels, + gid); + + ProcArrayRemove(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 will be recycled if + * we fail after this point. It is still locked by our backend 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) + { + delrels = commitrels; + ndelrels = hdr->ncommitrels; + } + else + { + delrels = abortrels; + ndelrels = hdr->nabortrels; + } + + /* Make sure files supposed to be dropped are dropped */ + DropRelationFiles(delrels, ndelrels, false); + + /* + * Handle cache invalidation messages. + * + * Relcache init file invalidation requires processing both before and + * after we send the SI messages. See AtEOXact_Inval() + */ + if (hdr->initfileinval) + RelationCacheInitFilePreInvalidate(); + SendSharedInvalidMessages(invalmsgs, hdr->ninvalmsgs); + if (hdr->initfileinval) + RelationCacheInitFilePostInvalidate(); + + /* + * Acquire the two-phase lock. We want to work on the two-phase callbacks + * while holding it to avoid potential conflicts with other transactions + * attempting to use the same GID, so the lock is released once the shared + * memory state is cleared. + */ + LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE); + + /* And now do the callbacks */ + if (isCommit) + ProcessRecords(bufptr, xid, twophase_postcommit_callbacks); + else + ProcessRecords(bufptr, xid, twophase_postabort_callbacks); + + PredicateLockTwoPhaseFinish(xid, isCommit); + + /* Clear shared memory state */ + RemoveGXact(gxact); + + /* + * Release the lock as all callbacks are called and shared memory cleanup + * is done. + */ + LWLockRelease(TwoPhaseStateLock); + + /* Count the prepared xact as committed or aborted */ + AtEOXact_PgStat(isCommit, false); + + /* + * And now we can clean up any files we may have left. + */ + if (gxact->ondisk) + RemoveTwoPhaseFile(xid, true); + + MyLockedGxact = NULL; + + RESUME_INTERRUPTS(); + + pfree(buf); +} + +/* + * Scan 2PC state data in memory 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. + */ +static 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 file \"%s\": %m", path))); +} + +/* + * Recreates a state file. This is used in WAL replay and during + * checkpoint creation. + * + * Note: content and len don't include CRC. + */ +static void +RecreateTwoPhaseFile(TransactionId xid, void *content, int len) +{ + char path[MAXPGPATH]; + pg_crc32c statefile_crc; + int fd; + + /* Recompute CRC */ + INIT_CRC32C(statefile_crc); + COMP_CRC32C(statefile_crc, content, len); + FIN_CRC32C(statefile_crc); + + TwoPhaseFilePath(path, xid); + + fd = OpenTransientFile(path, + O_CREAT | O_TRUNC | O_WRONLY | PG_BINARY); + if (fd < 0) + ereport(ERROR, + (errcode_for_file_access(), + errmsg("could not recreate file \"%s\": %m", path))); + + /* Write content and CRC */ + errno = 0; + pgstat_report_wait_start(WAIT_EVENT_TWOPHASE_FILE_WRITE); + if (write(fd, content, len) != len) + { + /* if write didn't set errno, assume problem is no disk space */ + if (errno == 0) + errno = ENOSPC; + ereport(ERROR, + (errcode_for_file_access(), + errmsg("could not write file \"%s\": %m", path))); + } + if (write(fd, &statefile_crc, sizeof(pg_crc32c)) != sizeof(pg_crc32c)) + { + /* if write didn't set errno, assume problem is no disk space */ + if (errno == 0) + errno = ENOSPC; + ereport(ERROR, + (errcode_for_file_access(), + errmsg("could not write file \"%s\": %m", path))); + } + pgstat_report_wait_end(); + + /* + * 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. + */ + pgstat_report_wait_start(WAIT_EVENT_TWOPHASE_FILE_SYNC); + if (pg_fsync(fd) != 0) + ereport(ERROR, + (errcode_for_file_access(), + errmsg("could not fsync file \"%s\": %m", path))); + pgstat_report_wait_end(); + + if (CloseTransientFile(fd) != 0) + ereport(ERROR, + (errcode_for_file_access(), + errmsg("could not close file \"%s\": %m", path))); +} + +/* + * CheckPointTwoPhase -- handle 2PC component of checkpointing. + * + * We must fsync the state file of any GXACT that is valid or has been + * generated during redo and has a PREPARE LSN <= the checkpoint's redo + * horizon. (If the gxact isn't valid yet, has not been generated in + * redo, 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. With typical checkpoint settings this + * will be about 3 minutes for an online checkpoint, so as a result we + * expect that there will be no GXACTs that need to be copied to disk. + * + * If a GXACT remains valid across multiple checkpoints, it will already + * be on disk so we don't bother to repeat that write. + */ +void +CheckPointTwoPhase(XLogRecPtr redo_horizon) +{ + int i; + int serialized_xacts = 0; + + if (max_prepared_xacts <= 0) + return; /* nothing to do */ + + TRACE_POSTGRESQL_TWOPHASE_CHECKPOINT_START(); + + /* + * We are expecting there to be zero GXACTs that need to be copied to + * disk, so we perform all I/O while holding TwoPhaseStateLock for + * simplicity. This prevents any new xacts from preparing while this + * occurs, which shouldn't be a problem since the presence of long-lived + * prepared xacts indicates the transaction manager isn't active. + * + * It's also possible to move I/O out of the lock, but on every error we + * should check whether somebody committed our transaction in different + * backend. Let's leave this optimization for future, if somebody will + * spot that this place cause bottleneck. + * + * Note that it isn't possible for there to be a GXACT with a + * prepare_end_lsn set prior to the last checkpoint yet is marked invalid, + * because of the efforts with delayChkpt. + */ + LWLockAcquire(TwoPhaseStateLock, LW_SHARED); + for (i = 0; i < TwoPhaseState->numPrepXacts; i++) + { + /* + * Note that we are using gxact not pgxact so this works in recovery + * also + */ + GlobalTransaction gxact = TwoPhaseState->prepXacts[i]; + + if ((gxact->valid || gxact->inredo) && + !gxact->ondisk && + gxact->prepare_end_lsn <= redo_horizon) + { + char *buf; + int len; + + XlogReadTwoPhaseData(gxact->prepare_start_lsn, &buf, &len); + RecreateTwoPhaseFile(gxact->xid, buf, len); + gxact->ondisk = true; + gxact->prepare_start_lsn = InvalidXLogRecPtr; + gxact->prepare_end_lsn = InvalidXLogRecPtr; + pfree(buf); + serialized_xacts++; + } + } + LWLockRelease(TwoPhaseStateLock); + + /* + * Flush unconditionally the parent directory to make any information + * durable on disk. Two-phase files could have been removed and those + * removals need to be made persistent as well as any files newly created + * previously since the last checkpoint. + */ + fsync_fname(TWOPHASE_DIR, true); + + TRACE_POSTGRESQL_TWOPHASE_CHECKPOINT_DONE(); + + if (log_checkpoints && serialized_xacts > 0) + ereport(LOG, + (errmsg_plural("%u two-phase state file was written " + "for a long-running prepared transaction", + "%u two-phase state files were written " + "for long-running prepared transactions", + serialized_xacts, + serialized_xacts))); +} + +/* + * restoreTwoPhaseData + * + * Scan pg_twophase and fill TwoPhaseState depending on the on-disk data. + * This is called once at the beginning of recovery, saving any extra + * lookups in the future. Two-phase files that are newer than the + * minimum XID horizon are discarded on the way. + */ +void +restoreTwoPhaseData(void) +{ + DIR *cldir; + struct dirent *clde; + + LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE); + 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; + + xid = (TransactionId) strtoul(clde->d_name, NULL, 16); + + buf = ProcessTwoPhaseBuffer(xid, InvalidXLogRecPtr, + true, false, false); + if (buf == NULL) + continue; + + PrepareRedoAdd(buf, InvalidXLogRecPtr, + InvalidXLogRecPtr, InvalidRepOriginId); + } + } + LWLockRelease(TwoPhaseStateLock); + FreeDir(cldir); +} + +/* + * PrescanPreparedTransactions + * + * Scan the shared memory entries of TwoPhaseState and determine the range + * of valid XIDs present. This is run during database startup, after we + * have completed reading WAL. ShmemVariableCache->nextFullXid 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 nextFullXid --- 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 nextFullXid 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. + * + * On corrupted two-phase files, fail immediately. Keeping around broken + * entries and let replay continue causes harm on the system, and a new + * backup should be rolled in. + * + * Our other responsibility is to determine and return the oldest valid XID + * among the prepared xacts (if none, return ShmemVariableCache->nextFullXid). + * This is needed to synchronize pg_subtrans startup properly. + * + * If xids_p and nxids_p are not NULL, pointer to a palloc'd array of all + * top-level xids is stored in *xids_p. The number of entries in the array + * is returned in *nxids_p. + */ +TransactionId +PrescanPreparedTransactions(TransactionId **xids_p, int *nxids_p) +{ + FullTransactionId nextFullXid = ShmemVariableCache->nextFullXid; + TransactionId origNextXid = XidFromFullTransactionId(nextFullXid); + TransactionId result = origNextXid; + TransactionId *xids = NULL; + int nxids = 0; + int allocsize = 0; + int i; + + LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE); + for (i = 0; i < TwoPhaseState->numPrepXacts; i++) + { + TransactionId xid; + char *buf; + GlobalTransaction gxact = TwoPhaseState->prepXacts[i]; + + Assert(gxact->inredo); + + xid = gxact->xid; + + buf = ProcessTwoPhaseBuffer(xid, + gxact->prepare_start_lsn, + gxact->ondisk, false, true); + + if (buf == NULL) + continue; + + /* + * OK, we think this file is valid. Incorporate xid into the + * running-minimum result. + */ + if (TransactionIdPrecedes(xid, result)) + result = xid; + + if (xids_p) + { + if (nxids == allocsize) + { + if (nxids == 0) + { + allocsize = 10; + xids = palloc(allocsize * sizeof(TransactionId)); + } + else + { + allocsize = allocsize * 2; + xids = repalloc(xids, allocsize * sizeof(TransactionId)); + } + } + xids[nxids++] = xid; + } + + pfree(buf); + } + LWLockRelease(TwoPhaseStateLock); + + if (xids_p) + { + *xids_p = xids; + *nxids_p = nxids; + } + + return result; +} + +/* + * StandbyRecoverPreparedTransactions + * + * Scan the shared memory entries of TwoPhaseState and setup all the required + * information to allow standby queries to treat prepared transactions as still + * active. + * + * This is never called at the end of recovery - we use + * RecoverPreparedTransactions() at that point. + * + * The lack of calls to SubTransSetParent() calls here is by design; + * those calls are made by RecoverPreparedTransactions() at the end of recovery + * for those xacts that need this. + */ +void +StandbyRecoverPreparedTransactions(void) +{ + int i; + + LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE); + for (i = 0; i < TwoPhaseState->numPrepXacts; i++) + { + TransactionId xid; + char *buf; + GlobalTransaction gxact = TwoPhaseState->prepXacts[i]; + + Assert(gxact->inredo); + + xid = gxact->xid; + + buf = ProcessTwoPhaseBuffer(xid, + gxact->prepare_start_lsn, + gxact->ondisk, false, false); + if (buf != NULL) + pfree(buf); + } + LWLockRelease(TwoPhaseStateLock); +} + +/* + * RecoverPreparedTransactions + * + * Scan the shared memory entries of TwoPhaseState and reload the state for + * each prepared transaction (reacquire locks, etc). + * + * This is run at the end of recovery, but before we allow backends to write + * WAL. + * + * At the end of recovery the way we take snapshots will change. We now need + * to mark all running transactions with their full SubTransSetParent() info + * to allow normal snapshots to work correctly if snapshots overflow. + * We do this here because by definition prepared transactions are the only + * type of write transaction still running, so this is necessary and + * complete. + */ +void +RecoverPreparedTransactions(void) +{ + int i; + + LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE); + for (i = 0; i < TwoPhaseState->numPrepXacts; i++) + { + TransactionId xid; + char *buf; + GlobalTransaction gxact = TwoPhaseState->prepXacts[i]; + char *bufptr; + TwoPhaseFileHeader *hdr; + TransactionId *subxids; + const char *gid; + + xid = gxact->xid; + + /* + * 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. It's possible that + * SubTransSetParent has been set before, if the prepared transaction + * generated xid assignment records. + */ + buf = ProcessTwoPhaseBuffer(xid, + gxact->prepare_start_lsn, + gxact->ondisk, true, false); + if (buf == NULL) + continue; + + ereport(LOG, + (errmsg("recovering prepared transaction %u from shared memory", xid))); + + hdr = (TwoPhaseFileHeader *) buf; + Assert(TransactionIdEquals(hdr->xid, xid)); + bufptr = buf + MAXALIGN(sizeof(TwoPhaseFileHeader)); + gid = (const char *) bufptr; + bufptr += MAXALIGN(hdr->gidlen); + subxids = (TransactionId *) bufptr; + bufptr += MAXALIGN(hdr->nsubxacts * sizeof(TransactionId)); + bufptr += MAXALIGN(hdr->ncommitrels * sizeof(RelFileNode)); + bufptr += MAXALIGN(hdr->nabortrels * sizeof(RelFileNode)); + bufptr += MAXALIGN(hdr->ninvalmsgs * sizeof(SharedInvalidationMessage)); + + /* + * Recreate its GXACT and dummy PGPROC. But, check whether it was + * added in redo and already has a shmem entry for it. + */ + MarkAsPreparingGuts(gxact, xid, gid, + hdr->prepared_at, + hdr->owner, hdr->database); + + /* recovered, so reset the flag for entries generated by redo */ + gxact->inredo = false; + + GXactLoadSubxactData(gxact, hdr->nsubxacts, subxids); + MarkAsPrepared(gxact, true); + + LWLockRelease(TwoPhaseStateLock); + + /* + * Recover other state (notably locks) using resource managers. + */ + ProcessRecords(bufptr, xid, twophase_recover_callbacks); + + /* + * Release locks held by the standby process after we process each + * prepared transaction. As a result, we don't need too many + * additional locks at any one time. + */ + if (InHotStandby) + StandbyReleaseLockTree(xid, hdr->nsubxacts, subxids); + + /* + * We're done with recovering this transaction. Clear MyLockedGxact, + * like we do in PrepareTransaction() during normal operation. + */ + PostPrepare_Twophase(); + + pfree(buf); + + LWLockAcquire(TwoPhaseStateLock, LW_EXCLUSIVE); + } + + LWLockRelease(TwoPhaseStateLock); +} + +/* + * ProcessTwoPhaseBuffer + * + * Given a transaction id, read it either from disk or read it directly + * via shmem xlog record pointer using the provided "prepare_start_lsn". + * + * If setParent is true, set up subtransaction parent linkages. + * + * If setNextXid is true, set ShmemVariableCache->nextFullXid to the newest + * value scanned. + */ +static char * +ProcessTwoPhaseBuffer(TransactionId xid, + XLogRecPtr prepare_start_lsn, + bool fromdisk, + bool setParent, bool setNextXid) +{ + FullTransactionId nextFullXid = ShmemVariableCache->nextFullXid; + TransactionId origNextXid = XidFromFullTransactionId(nextFullXid); + TransactionId *subxids; + char *buf; + TwoPhaseFileHeader *hdr; + int i; + + Assert(LWLockHeldByMeInMode(TwoPhaseStateLock, LW_EXCLUSIVE)); + + if (!fromdisk) + Assert(prepare_start_lsn != InvalidXLogRecPtr); + + /* Already processed? */ + if (TransactionIdDidCommit(xid) || TransactionIdDidAbort(xid)) + { + if (fromdisk) + { + ereport(WARNING, + (errmsg("removing stale two-phase state file for transaction %u", + xid))); + RemoveTwoPhaseFile(xid, true); + } + else + { + ereport(WARNING, + (errmsg("removing stale two-phase state from memory for transaction %u", + xid))); + PrepareRedoRemove(xid, true); + } + return NULL; + } + + /* Reject XID if too new */ + if (TransactionIdFollowsOrEquals(xid, origNextXid)) + { + if (fromdisk) + { + ereport(WARNING, + (errmsg("removing future two-phase state file for transaction %u", + xid))); + RemoveTwoPhaseFile(xid, true); + } + else + { + ereport(WARNING, + (errmsg("removing future two-phase state from memory for transaction %u", + xid))); + PrepareRedoRemove(xid, true); + } + return NULL; + } + + if (fromdisk) + { + /* Read and validate file */ + buf = ReadTwoPhaseFile(xid, false); + } + else + { + /* Read xlog data */ + XlogReadTwoPhaseData(prepare_start_lsn, &buf, NULL); + } + + /* Deconstruct header */ + hdr = (TwoPhaseFileHeader *) buf; + if (!TransactionIdEquals(hdr->xid, xid)) + { + if (fromdisk) + ereport(ERROR, + (errcode(ERRCODE_DATA_CORRUPTED), + errmsg("corrupted two-phase state file for transaction %u", + xid))); + else + ereport(ERROR, + (errcode(ERRCODE_DATA_CORRUPTED), + errmsg("corrupted two-phase state in memory for transaction %u", + xid))); + } + + /* + * Examine subtransaction XIDs ... they should all follow main XID, and + * they may force us to advance nextFullXid. + */ + subxids = (TransactionId *) (buf + + MAXALIGN(sizeof(TwoPhaseFileHeader)) + + MAXALIGN(hdr->gidlen)); + for (i = 0; i < hdr->nsubxacts; i++) + { + TransactionId subxid = subxids[i]; + + Assert(TransactionIdFollows(subxid, xid)); + + /* update nextFullXid if needed */ + if (setNextXid) + AdvanceNextFullTransactionIdPastXid(subxid); + + if (setParent) + SubTransSetParent(subxid, xid); + } + + return buf; +} + + +/* + * RecordTransactionCommitPrepared + * + * This is basically the same as RecordTransactionCommit (q.v. if you change + * this function): in particular, we must set the delayChkpt 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, + int ninvalmsgs, + SharedInvalidationMessage *invalmsgs, + bool initfileinval, + const char *gid) +{ + XLogRecPtr recptr; + TimestampTz committs = GetCurrentTimestamp(); + bool replorigin; + + /* + * Are we using the replication origins feature? Or, in other words, are + * we replaying remote actions? + */ + replorigin = (replorigin_session_origin != InvalidRepOriginId && + replorigin_session_origin != DoNotReplicateId); + + START_CRIT_SECTION(); + + /* See notes in RecordTransactionCommit */ + MyProc->delayChkpt = true; + + /* + * Emit the XLOG commit record. Note that we mark 2PC commits as + * potentially having AccessExclusiveLocks since we don't know whether or + * not they do. + */ + recptr = XactLogCommitRecord(committs, + nchildren, children, nrels, rels, + ninvalmsgs, invalmsgs, + initfileinval, false, + MyXactFlags | XACT_FLAGS_ACQUIREDACCESSEXCLUSIVELOCK, + xid, gid); + + + if (replorigin) + /* Move LSNs forward for this replication origin */ + replorigin_session_advance(replorigin_session_origin_lsn, + XactLastRecEnd); + + /* + * Record commit timestamp. The value comes from plain commit timestamp + * if replorigin is not enabled, or replorigin already set a value for us + * in replorigin_session_origin_timestamp otherwise. + * + * We don't need to WAL-log anything here, as the commit record written + * above already contains the data. + */ + if (!replorigin || replorigin_session_origin_timestamp == 0) + replorigin_session_origin_timestamp = committs; + + TransactionTreeSetCommitTsData(xid, nchildren, children, + replorigin_session_origin_timestamp, + replorigin_session_origin, false); + + /* + * 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_xact */ + TransactionIdCommitTree(xid, nchildren, children); + + /* Checkpoint can proceed now */ + MyProc->delayChkpt = false; + + END_CRIT_SECTION(); + + /* + * Wait for synchronous replication, if required. + * + * Note that at this stage we have marked clog, but still show as running + * in the procarray and continue to hold locks. + */ + SyncRepWaitForLSN(recptr, true); +} + +/* + * 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, + const char *gid) +{ + 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 commit record. Note that we mark 2PC aborts as + * potentially having AccessExclusiveLocks since we don't know whether or + * not they do. + */ + recptr = XactLogAbortRecord(GetCurrentTimestamp(), + nchildren, children, + nrels, rels, + MyXactFlags | XACT_FLAGS_ACQUIREDACCESSEXCLUSIVELOCK, + xid, gid); + + /* 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. + */ + TransactionIdAbortTree(xid, nchildren, children); + + END_CRIT_SECTION(); + + /* + * Wait for synchronous replication, if required. + * + * Note that at this stage we have marked clog, but still show as running + * in the procarray and continue to hold locks. + */ + SyncRepWaitForLSN(recptr, false); +} + +/* + * PrepareRedoAdd + * + * Store pointers to the start/end of the WAL record along with the xid in + * a gxact entry in shared memory TwoPhaseState structure. If caller + * specifies InvalidXLogRecPtr as WAL location to fetch the two-phase + * data, the entry is marked as located on disk. + */ +void +PrepareRedoAdd(char *buf, XLogRecPtr start_lsn, + XLogRecPtr end_lsn, RepOriginId origin_id) +{ + TwoPhaseFileHeader *hdr = (TwoPhaseFileHeader *) buf; + char *bufptr; + const char *gid; + GlobalTransaction gxact; + + Assert(LWLockHeldByMeInMode(TwoPhaseStateLock, LW_EXCLUSIVE)); + Assert(RecoveryInProgress()); + + bufptr = buf + MAXALIGN(sizeof(TwoPhaseFileHeader)); + gid = (const char *) bufptr; + + /* + * Reserve the GID for the given transaction in the redo code path. + * + * This creates a gxact struct and puts it into the active array. + * + * In redo, this struct is mainly used to track PREPARE/COMMIT entries in + * shared memory. Hence, we only fill up the bare minimum contents here. + * The gxact also gets marked with gxact->inredo set to true to indicate + * that it got added in the redo phase + */ + + /* Get a free gxact from the freelist */ + if (TwoPhaseState->freeGXacts == NULL) + 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 = TwoPhaseState->freeGXacts; + TwoPhaseState->freeGXacts = gxact->next; + + gxact->prepared_at = hdr->prepared_at; + gxact->prepare_start_lsn = start_lsn; + gxact->prepare_end_lsn = end_lsn; + gxact->xid = hdr->xid; + gxact->owner = hdr->owner; + gxact->locking_backend = InvalidBackendId; + gxact->valid = false; + gxact->ondisk = XLogRecPtrIsInvalid(start_lsn); + gxact->inredo = true; /* yes, added in redo */ + strcpy(gxact->gid, gid); + + /* And insert it into the active array */ + Assert(TwoPhaseState->numPrepXacts < max_prepared_xacts); + TwoPhaseState->prepXacts[TwoPhaseState->numPrepXacts++] = gxact; + + if (origin_id != InvalidRepOriginId) + { + /* recover apply progress */ + replorigin_advance(origin_id, hdr->origin_lsn, end_lsn, + false /* backward */ , false /* WAL */ ); + } + + elog(DEBUG2, "added 2PC data in shared memory for transaction %u", gxact->xid); +} + +/* + * PrepareRedoRemove + * + * Remove the corresponding gxact entry from TwoPhaseState. Also remove + * the 2PC file if a prepared transaction was saved via an earlier checkpoint. + * + * Caller must hold TwoPhaseStateLock in exclusive mode, because TwoPhaseState + * is updated. + */ +void +PrepareRedoRemove(TransactionId xid, bool giveWarning) +{ + GlobalTransaction gxact = NULL; + int i; + bool found = false; + + Assert(LWLockHeldByMeInMode(TwoPhaseStateLock, LW_EXCLUSIVE)); + Assert(RecoveryInProgress()); + + for (i = 0; i < TwoPhaseState->numPrepXacts; i++) + { + gxact = TwoPhaseState->prepXacts[i]; + + if (gxact->xid == xid) + { + Assert(gxact->inredo); + found = true; + break; + } + } + + /* + * Just leave if there is nothing, this is expected during WAL replay. + */ + if (!found) + return; + + /* + * And now we can clean up any files we may have left. + */ + elog(DEBUG2, "removing 2PC data for transaction %u", xid); + if (gxact->ondisk) + RemoveTwoPhaseFile(xid, giveWarning); + RemoveGXact(gxact); +} |