xact.c

postgresql8.3.4源码,开源数据库

static void
AtCleanup_Memory(void)
{
	Assert(CurrentTransactionState->parent == NULL);

	/*
	 * Now that we're "out" of a transaction, have the system allocate things
	 * in the top memory context instead of per-transaction contexts.
	 */
	MemoryContextSwitchTo(TopMemoryContext);

	/*
	 * Clear the special abort context for next time.
	 */
	if (TransactionAbortContext != NULL)
		MemoryContextResetAndDeleteChildren(TransactionAbortContext);

	/*
	 * Release all transaction-local memory.
	 */
	if (TopTransactionContext != NULL)
		MemoryContextDelete(TopTransactionContext);
	TopTransactionContext = NULL;
	CurTransactionContext = NULL;
	CurrentTransactionState->curTransactionContext = NULL;
}


/* ----------------------------------------------------------------
 *						CleanupSubTransaction stuff
 * ----------------------------------------------------------------
 */

/*
 * AtSubCleanup_Memory
 */
static void
AtSubCleanup_Memory(void)
{
	TransactionState s = CurrentTransactionState;

	Assert(s->parent != NULL);

	/* Make sure we're not in an about-to-be-deleted context */
	MemoryContextSwitchTo(s->parent->curTransactionContext);
	CurTransactionContext = s->parent->curTransactionContext;

	/*
	 * Clear the special abort context for next time.
	 */
	if (TransactionAbortContext != NULL)
		MemoryContextResetAndDeleteChildren(TransactionAbortContext);

	/*
	 * Delete the subxact local memory contexts. Its CurTransactionContext can
	 * go too (note this also kills CurTransactionContexts from any children
	 * of the subxact).
	 */
	if (s->curTransactionContext)
		MemoryContextDelete(s->curTransactionContext);
	s->curTransactionContext = NULL;
}

/* ----------------------------------------------------------------
 *						interface routines
 * ----------------------------------------------------------------
 */

/*
 *	StartTransaction
 */
static void
StartTransaction(void)
{
	TransactionState s;
	VirtualTransactionId vxid;

	/*
	 * Let's just make sure the state stack is empty
	 */
	s = &TopTransactionStateData;
	CurrentTransactionState = s;

	/*
	 * check the current transaction state
	 */
	if (s->state != TRANS_DEFAULT)
		elog(WARNING, "StartTransaction while in %s state",
			 TransStateAsString(s->state));

	/*
	 * set the current transaction state information appropriately during
	 * start processing
	 */
	s->state = TRANS_START;
	s->transactionId = InvalidTransactionId;	/* until assigned */

	/*
	 * Make sure we've freed any old snapshot, and reset xact state variables
	 */
	FreeXactSnapshot();
	XactIsoLevel = DefaultXactIsoLevel;
	XactReadOnly = DefaultXactReadOnly;
	forceSyncCommit = false;
	MyXactAccessedTempRel = false;

	/*
	 * reinitialize within-transaction counters
	 */
	s->subTransactionId = TopSubTransactionId;
	currentSubTransactionId = TopSubTransactionId;
	currentCommandId = FirstCommandId;
	currentCommandIdUsed = false;

	/*
	 * must initialize resource-management stuff first
	 */
	AtStart_Memory();
	AtStart_ResourceOwner();

	/*
	 * Assign a new LocalTransactionId, and combine it with the backendId to
	 * form a virtual transaction id.
	 */
	vxid.backendId = MyBackendId;
	vxid.localTransactionId = GetNextLocalTransactionId();

	/*
	 * Lock the virtual transaction id before we announce it in the proc array
	 */
	VirtualXactLockTableInsert(vxid);

	/*
	 * Advertise it in the proc array.	We assume assignment of
	 * LocalTransactionID is atomic, and the backendId should be set already.
	 */
	Assert(MyProc->backendId == vxid.backendId);
	MyProc->lxid = vxid.localTransactionId;

	PG_TRACE1(transaction__start, vxid.localTransactionId);

	/*
	 * set transaction_timestamp() (a/k/a now()).  We want this to be the same
	 * as the first command's statement_timestamp(), so don't do a fresh
	 * GetCurrentTimestamp() call (which'd be expensive anyway).  Also, mark
	 * xactStopTimestamp as unset.
	 */
	xactStartTimestamp = stmtStartTimestamp;
	xactStopTimestamp = 0;
	pgstat_report_xact_timestamp(xactStartTimestamp);

	/*
	 * initialize current transaction state fields
	 *
	 * note: prevXactReadOnly is not used at the outermost level
	 */
	s->nestingLevel = 1;
	s->gucNestLevel = 1;
	s->childXids = NULL;
	s->nChildXids = 0;
	s->maxChildXids = 0;
	GetUserIdAndContext(&s->prevUser, &s->prevSecDefCxt);
	/* SecurityDefinerContext should never be set outside a transaction */
	Assert(!s->prevSecDefCxt);

	/*
	 * initialize other subsystems for new transaction
	 */
	AtStart_GUC();
	AtStart_Inval();
	AtStart_Cache();
	AfterTriggerBeginXact();

	/*
	 * done with start processing, set current transaction state to "in
	 * progress"
	 */
	s->state = TRANS_INPROGRESS;

	ShowTransactionState("StartTransaction");
}


/*
 *	CommitTransaction
 *
 * NB: if you change this routine, better look at PrepareTransaction too!
 */
static void
CommitTransaction(void)
{
	TransactionState s = CurrentTransactionState;
	TransactionId latestXid;

	ShowTransactionState("CommitTransaction");

	/*
	 * check the current transaction state
	 */
	if (s->state != TRANS_INPROGRESS)
		elog(WARNING, "CommitTransaction while in %s state",
			 TransStateAsString(s->state));
	Assert(s->parent == NULL);

	/*
	 * Do pre-commit processing (most of this stuff requires database access,
	 * and in fact could still cause an error...)
	 *
	 * It is possible for CommitHoldablePortals to invoke functions that queue
	 * deferred triggers, and it's also possible that triggers create holdable
	 * cursors.  So we have to loop until there's nothing left to do.
	 */
	for (;;)
	{
		/*
		 * Fire all currently pending deferred triggers.
		 */
		AfterTriggerFireDeferred();

		/*
		 * Convert any open holdable cursors into static portals.  If there
		 * weren't any, we are done ... otherwise loop back to check if they
		 * queued deferred triggers.  Lather, rinse, repeat.
		 */
		if (!CommitHoldablePortals())
			break;
	}

	/* Now we can shut down the deferred-trigger manager */
	AfterTriggerEndXact(true);

	/* Close any open regular cursors */
	AtCommit_Portals();

	/*
	 * Let ON COMMIT management do its thing (must happen after closing
	 * cursors, to avoid dangling-reference problems)
	 */
	PreCommit_on_commit_actions();

	/* close large objects before lower-level cleanup */
	AtEOXact_LargeObject(true);

	/* NOTIFY commit must come before lower-level cleanup */
	AtCommit_Notify();

	/*
	 * Update flat files if we changed pg_database, pg_authid or
	 * pg_auth_members.  This should be the last step before commit.
	 */
	AtEOXact_UpdateFlatFiles(true);

	/* Prevent cancel/die interrupt while cleaning up */
	HOLD_INTERRUPTS();

	/*
	 * set the current transaction state information appropriately during
	 * commit processing
	 */
	s->state = TRANS_COMMIT;

	/*
	 * Here is where we really truly commit.
	 */
	latestXid = RecordTransactionCommit();

	PG_TRACE1(transaction__commit, MyProc->lxid);

	/*
	 * Let others know about no transaction in progress by me. Note that this
	 * must be done _before_ releasing locks we hold and _after_
	 * RecordTransactionCommit.
	 */
	ProcArrayEndTransaction(MyProc, latestXid);

	/*
	 * This is all post-commit cleanup.  Note that if an error is raised here,
	 * it's too late to abort the transaction.  This should be just
	 * noncritical resource releasing.
	 *
	 * The ordering of operations is not entirely random.  The idea is:
	 * release resources visible to other backends (eg, files, buffer pins);
	 * then release locks; then release backend-local resources. We want to
	 * release locks at the point where any backend waiting for us will see
	 * our transaction as being fully cleaned up.
	 *
	 * Resources that can be associated with individual queries are handled by
	 * the ResourceOwner mechanism.  The other calls here are for backend-wide
	 * state.
	 */

	CallXactCallbacks(XACT_EVENT_COMMIT);

	ResourceOwnerRelease(TopTransactionResourceOwner,
						 RESOURCE_RELEASE_BEFORE_LOCKS,
						 true, true);

	/* Check we've released all buffer pins */
	AtEOXact_Buffers(true);

	/* Clean up the relation cache */
	AtEOXact_RelationCache(true);

	/*
	 * Make catalog changes visible to all backends.  This has to happen after
	 * relcache references are dropped (see comments for
	 * AtEOXact_RelationCache), but before locks are released (if anyone is
	 * waiting for lock on a relation we've modified, we want them to know
	 * about the catalog change before they start using the relation).
	 */
	AtEOXact_Inval(true);

	/*
	 * Likewise, dropping of files deleted during the transaction is best done
	 * after releasing relcache and buffer pins.  (This is not strictly
	 * necessary during commit, since such pins should have been released
	 * already, but this ordering is definitely critical during abort.)
	 */
	smgrDoPendingDeletes(true);

	AtEOXact_MultiXact();

	ResourceOwnerRelease(TopTransactionResourceOwner,
						 RESOURCE_RELEASE_LOCKS,
						 true, true);
	ResourceOwnerRelease(TopTransactionResourceOwner,
						 RESOURCE_RELEASE_AFTER_LOCKS,
						 true, true);

	/* Check we've released all catcache entries */
	AtEOXact_CatCache(true);

	AtEOXact_GUC(true, 1);
	AtEOXact_SPI(true);
	AtEOXact_xml();
	AtEOXact_on_commit_actions(true);
	AtEOXact_Namespace(true);
	/* smgrcommit already done */
	AtEOXact_Files();
	AtEOXact_ComboCid();
	AtEOXact_HashTables(true);
	AtEOXact_PgStat(true);
	pgstat_report_xact_timestamp(0);

	CurrentResourceOwner = NULL;
	ResourceOwnerDelete(TopTransactionResourceOwner);
	s->curTransactionOwner = NULL;
	CurTransactionResourceOwner = NULL;
	TopTransactionResourceOwner = NULL;

	AtCommit_Memory();

	s->transactionId = InvalidTransactionId;
	s->subTransactionId = InvalidSubTransactionId;
	s->nestingLevel = 0;
	s->gucNestLevel = 0;
	s->childXids = NULL;
	s->nChildXids = 0;
	s->maxChildXids = 0;

	/*
	 * done with commit processing, set current transaction state back to
	 * default
	 */
	s->state = TRANS_DEFAULT;

	RESUME_INTERRUPTS();
}


/*
 *	PrepareTransaction
 *
 * NB: if you change this routine, better look at CommitTransaction too!
 */
static void
PrepareTransaction(void)
{
	TransactionState s = CurrentTransactionState;
	TransactionId xid = GetCurrentTransactionId();
	GlobalTransaction gxact;
	TimestampTz prepared_at;

	ShowTransactionState("PrepareTransaction");

	/*
	 * check the current transaction state
	 */
	if (s->state != TRANS_INPROGRESS)
		elog(WARNING, "PrepareTransaction while in %s state",
			 TransStateAsString(s->state));
	Assert(s->parent == NULL);

	/*
	 * Do pre-commit processing (most of this stuff requires database access,
	 * and in fact could still cause an error...)
	 *
	 * It is possible for PrepareHoldablePortals to invoke functions that
	 * queue deferred triggers, and it's also possible that triggers create
	 * holdable cursors.  So we have to loop until there's nothing left to do.
	 */
	for (;;)
	{
		/*
		 * Fire all currently pending deferred triggers.
		 */
		AfterTriggerFireDeferred();

		/*
		 * Convert any open holdable cursors into static portals.  If there
		 * weren't any, we are done ... otherwise loop back to check if they
		 * queued deferred triggers.  Lather, rinse, repeat.
		 */
		if (!PrepareHoldablePortals())
			break;
	}

	/* Now we can shut down the deferred-trigger manager */
	AfterTriggerEndXact(true);

	/* Close any open regular cursors */
	AtCommit_Portals();

	/*
	 * Let ON COMMIT management do its thing (must happen after closing
	 * cursors, to avoid dangling-reference problems)
	 */
	PreCommit_on_commit_actions();

	/* close large objects before lower-level cleanup */
	AtEOXact_LargeObject(true);

	/* NOTIFY and flatfiles will be handled below */

	/*
	 * Don't allow PREPARE TRANSACTION if we've accessed a temporary table
	 * in this transaction.  Having the prepared xact hold locks on another
	 * backend's temp table seems a bad idea --- for instance it would prevent
	 * the backend from exiting.  There are other problems too, such as how
	 * to clean up the source backend's local buffers and ON COMMIT state
	 * if the prepared xact includes a DROP of a temp table.
	 *
	 * We must check this after executing any ON COMMIT actions, because
	 * they might still access a temp relation.
	 *
	 * XXX In principle this could be relaxed to allow some useful special
	 * cases, such as a temp table created and dropped all within the
	 * transaction.  That seems to require much more bookkeeping though.
	 */
	if (MyXactAccessedTempRel)
		ereport(ERROR,
				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
				 errmsg("cannot PREPARE a transaction that has operated on temporary tables")));

	/* Prevent cancel/die interrupt while cleaning up */
	HOLD_INTERRUPTS();

	/*
	 * set the current transaction state information appropriately during
	 * prepare processing
	 */
	s->state = TRANS_PREPARE;

	prepared_at = GetCurrentTimestamp();

	/* Tell bufmgr and smgr to prepare for commit */
	BufmgrCommit();

	/*
	 * Reserve the GID for this transaction. This could fail if the requested