xact.c

来自「PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统」· C语言 代码 · 共 2,442 行 · 第 1/5 页

		/*
		 * Catch the scenario where we aborted partway through
		 * RecordTransactionCommit ...
		 */
		if (TransactionIdDidCommit(xid))
			elog(PANIC, "cannot abort transaction %u, it was already committed", xid);

		START_CRIT_SECTION();

		/*
		 * We only need to log the abort in XLOG if the transaction made any
		 * transaction-controlled XLOG entries or will delete files. (If it
		 * made no transaction-controlled XLOG entries, its XID appears
		 * nowhere in permanent storage, so no one else will ever care if it
		 * committed.)
		 *
		 * We do not flush XLOG to disk unless deleting files, since the
		 * default assumption after a crash would be that we aborted, anyway.
		 * For the same reason, we don't need to worry about interlocking
		 * against checkpoint start.
		 */
		if (MyLastRecPtr.xrecoff != 0 || nrels > 0)
		{
			XLogRecData rdata[3];
			int			lastrdata = 0;
			xl_xact_abort xlrec;
			XLogRecPtr	recptr;

			xlrec.xtime = time(NULL);
			xlrec.nrels = nrels;
			xlrec.nsubxacts = nchildren;
			rdata[0].data = (char *) (&xlrec);
			rdata[0].len = MinSizeOfXactAbort;
			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, rdata);

			/* Must flush if we are deleting files... */
			if (nrels > 0)
				XLogFlush(recptr);
		}

		/*
		 * Mark the transaction aborted in clog.  This is not absolutely
		 * necessary but we may as well do it while we are here.
		 *
		 * The ordering here isn't critical but it seems best to mark the
		 * parent first.  This assures an atomic transition of all the
		 * subtransactions to aborted state from the point of view of
		 * concurrent TransactionIdDidAbort calls.
		 */
		TransactionIdAbort(xid);
		TransactionIdAbortTree(nchildren, children);

		END_CRIT_SECTION();
	}

	/* Break the chain of back-links in the XLOG records I output */
	MyLastRecPtr.xrecoff = 0;
	MyXactMadeXLogEntry = false;
	MyXactMadeTempRelUpdate = false;

	/* And clean up local data */
	if (rels)
		pfree(rels);
	if (children)
		pfree(children);
}

/*
 *	AtAbort_Memory
 */
static void
AtAbort_Memory(void)
{
	/*
	 * Make sure we are in a valid context (not a child of
	 * TopTransactionContext...).  Note that it is possible for this code to
	 * be called when we aren't in a transaction at all; go directly to
	 * TopMemoryContext in that case.
	 */
	if (TopTransactionContext != NULL)
	{
		MemoryContextSwitchTo(TopTransactionContext);

		/*
		 * We do not want to destroy the transaction's global state yet, so we
		 * can't free any memory here.
		 */
	}
	else
		MemoryContextSwitchTo(TopMemoryContext);
}

/*
 * AtSubAbort_Memory
 */
static void
AtSubAbort_Memory(void)
{
	Assert(TopTransactionContext != NULL);

	MemoryContextSwitchTo(TopTransactionContext);
}


/*
 *	AtAbort_ResourceOwner
 */
static void
AtAbort_ResourceOwner(void)
{
	/*
	 * Make sure we have a valid ResourceOwner, if possible (else it will be
	 * NULL, which is OK)
	 */
	CurrentResourceOwner = TopTransactionResourceOwner;
}

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

	/* Make sure we have a valid ResourceOwner */
	CurrentResourceOwner = s->curTransactionOwner;
}


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

	/*
	 * We keep the child-XID lists in TopTransactionContext (see
	 * AtSubCommit_childXids).	This means we'd better free the list
	 * explicitly at abort to avoid leakage.
	 */
	list_free(s->childXids);
	s->childXids = NIL;
}

/*
 * RecordSubTransactionAbort
 */
static void
RecordSubTransactionAbort(void)
{
	int			nrels;
	RelFileNode *rels;
	TransactionId xid = GetCurrentTransactionId();
	int			nchildren;
	TransactionId *children;

	/* Get data needed for abort record */
	nrels = smgrGetPendingDeletes(false, &rels);
	nchildren = xactGetCommittedChildren(&children);

	/*
	 * If we made neither any transaction-controlled XLOG entries nor any
	 * temp-rel updates, and are not going to delete any files, we can omit
	 * recording the transaction abort at all.	No one will ever care that it
	 * aborted.  (These tests cover our whole transaction tree, and therefore
	 * may mark subxacts that don't really need it, but it's probably not
	 * worth being tenser.)
	 *
	 * In this case we needn't worry about marking subcommitted children as
	 * aborted, because they didn't mark themselves as subcommitted in the
	 * first place; see the optimization in RecordSubTransactionCommit.
	 */
	if (MyLastRecPtr.xrecoff != 0 || MyXactMadeTempRelUpdate || nrels > 0)
	{
		START_CRIT_SECTION();

		/*
		 * We only need to log the abort in XLOG if the transaction made any
		 * transaction-controlled XLOG entries or will delete files.
		 */
		if (MyLastRecPtr.xrecoff != 0 || nrels > 0)
		{
			XLogRecData rdata[3];
			int			lastrdata = 0;
			xl_xact_abort xlrec;
			XLogRecPtr	recptr;

			xlrec.xtime = time(NULL);
			xlrec.nrels = nrels;
			xlrec.nsubxacts = nchildren;
			rdata[0].data = (char *) (&xlrec);
			rdata[0].len = MinSizeOfXactAbort;
			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, rdata);

			/* Must flush if we are deleting files... */
			if (nrels > 0)
				XLogFlush(recptr);
		}

		/*
		 * Mark the transaction aborted in clog.  This is not absolutely
		 * necessary but XactLockTableWait makes use of it to avoid waiting
		 * for already-aborted subtransactions.
		 */
		TransactionIdAbort(xid);
		TransactionIdAbortTree(nchildren, children);

		END_CRIT_SECTION();
	}

	/*
	 * We can immediately remove failed XIDs from PGPROC's cache of running
	 * child XIDs. It's easiest to do it here while we have the child XID
	 * array at hand, even though in the main-transaction case the equivalent
	 * work happens just after return from RecordTransactionAbort.
	 */
	XidCacheRemoveRunningXids(xid, nchildren, children);

	/* And clean up local data */
	if (rels)
		pfree(rels);
	if (children)
		pfree(children);
}

/* ----------------------------------------------------------------
 *						CleanupTransaction stuff
 * ----------------------------------------------------------------
 */

/*
 *	AtCleanup_Memory
 */
static void
AtCleanup_Memory(void)
{
	/*
	 * 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);

	Assert(CurrentTransactionState->parent == NULL);

	/*
	 * 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;

	/*
	 * 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;

	/*
	 * 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;

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

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

	/*
	 * generate a new transaction id
	 */
	s->transactionId = GetNewTransactionId(false);

	XactLockTableInsert(s->transactionId);

	/*
	 * set now()
	 */
	xactStartTimestamp = GetCurrentTimestamp();

	/*
	 * initialize current transaction state fields
	 */
	s->nestingLevel = 1;
	s->childXids = NIL;

	/*
	 * You might expect to see "s->currentUser = GetUserId();" here, but you
	 * won't because it doesn't work during startup; the userid isn't set yet
	 * during a backend's first transaction start.  We only use the
	 * currentUser field in sub-transaction state structs.
	 *
	 * prevXactReadOnly is also valid only in sub-transactions.
	 */

	/*
	 * initialize other subsystems for new transaction
	 */
	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;

	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();