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

}


/*
 *	CommandCounterIncrement
 */
void
CommandCounterIncrement(void)
{
	currentCommandId += 1;
	if (currentCommandId == FirstCommandId)		/* check for overflow */
	{
		currentCommandId -= 1;
		ereport(ERROR,
				(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
		  errmsg("cannot have more than 2^32-1 commands in a transaction")));
	}

	/* Propagate new command ID into static snapshots, if set */
	if (SerializableSnapshot)
		SerializableSnapshot->curcid = currentCommandId;
	if (LatestSnapshot)
		LatestSnapshot->curcid = currentCommandId;

	/*
	 * make cache changes visible to me.
	 */
	AtCommit_LocalCache();
	AtStart_Cache();
}


/* ----------------------------------------------------------------
 *						StartTransaction stuff
 * ----------------------------------------------------------------
 */

/*
 *	AtStart_Cache
 */
static void
AtStart_Cache(void)
{
	AcceptInvalidationMessages();
}

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

	/*
	 * We shouldn't have a transaction context already.
	 */
	Assert(TopTransactionContext == NULL);

	/*
	 * Create a toplevel context for the transaction.
	 */
	TopTransactionContext =
		AllocSetContextCreate(TopMemoryContext,
							  "TopTransactionContext",
							  ALLOCSET_DEFAULT_MINSIZE,
							  ALLOCSET_DEFAULT_INITSIZE,
							  ALLOCSET_DEFAULT_MAXSIZE);

	/*
	 * In a top-level transaction, CurTransactionContext is the same as
	 * TopTransactionContext.
	 */
	CurTransactionContext = TopTransactionContext;
	s->curTransactionContext = CurTransactionContext;

	/* Make the CurTransactionContext active. */
	MemoryContextSwitchTo(CurTransactionContext);
}

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

	/*
	 * We shouldn't have a transaction resource owner already.
	 */
	Assert(TopTransactionResourceOwner == NULL);

	/*
	 * Create a toplevel resource owner for the transaction.
	 */
	s->curTransactionOwner = ResourceOwnerCreate(NULL, "TopTransaction");

	TopTransactionResourceOwner = s->curTransactionOwner;
	CurTransactionResourceOwner = s->curTransactionOwner;
	CurrentResourceOwner = s->curTransactionOwner;
}

/* ----------------------------------------------------------------
 *						StartSubTransaction stuff
 * ----------------------------------------------------------------
 */

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

	Assert(CurTransactionContext != NULL);

	/*
	 * Create a CurTransactionContext, which will be used to hold data that
	 * survives subtransaction commit but disappears on subtransaction abort.
	 * We make it a child of the immediate parent's CurTransactionContext.
	 */
	CurTransactionContext = AllocSetContextCreate(CurTransactionContext,
												  "CurTransactionContext",
												  ALLOCSET_DEFAULT_MINSIZE,
												  ALLOCSET_DEFAULT_INITSIZE,
												  ALLOCSET_DEFAULT_MAXSIZE);
	s->curTransactionContext = CurTransactionContext;

	/* Make the CurTransactionContext active. */
	MemoryContextSwitchTo(CurTransactionContext);
}

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

	Assert(s->parent != NULL);

	/*
	 * Create a resource owner for the subtransaction.	We make it a child of
	 * the immediate parent's resource owner.
	 */
	s->curTransactionOwner =
		ResourceOwnerCreate(s->parent->curTransactionOwner,
							"SubTransaction");

	CurTransactionResourceOwner = s->curTransactionOwner;
	CurrentResourceOwner = s->curTransactionOwner;
}

/* ----------------------------------------------------------------
 *						CommitTransaction stuff
 * ----------------------------------------------------------------
 */

/*
 *	RecordTransactionCommit
 */
void
RecordTransactionCommit(void)
{
	int			nrels;
	RelFileNode *rels;
	int			nchildren;
	TransactionId *children;

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

	/*
	 * If we made neither any XLOG entries nor any temp-rel updates, and have
	 * no files to be deleted, we can omit recording the transaction commit at
	 * all.  (This test includes the effects of subtransactions, so the
	 * presence of committed subxacts need not alone force a write.)
	 */
	if (MyXactMadeXLogEntry || MyXactMadeTempRelUpdate || nrels > 0)
	{
		TransactionId xid = GetCurrentTransactionId();
		bool		madeTCentries;
		XLogRecPtr	recptr;

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

		START_CRIT_SECTION();

		/*
		 * If our transaction made any transaction-controlled XLOG entries, we
		 * need to lock out checkpoint start between writing our XLOG record
		 * and updating pg_clog.  Otherwise it is possible for the checkpoint
		 * to set REDO after the XLOG record but fail to flush the pg_clog
		 * update to disk, leading to loss of the transaction commit if we
		 * crash a little later.  Slightly klugy fix for problem discovered
		 * 2004-08-10.
		 *
		 * (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; so it doesn't matter if we lose the commit flag.)
		 *
		 * Note we only need a shared lock.
		 */
		madeTCentries = (MyLastRecPtr.xrecoff != 0);
		if (madeTCentries)
			LWLockAcquire(CheckpointStartLock, LW_SHARED);

		/*
		 * We only need to log the commit in XLOG if the transaction made any
		 * transaction-controlled XLOG entries or will delete files.
		 */
		if (madeTCentries || nrels > 0)
		{
			XLogRecData rdata[3];
			int			lastrdata = 0;
			xl_xact_commit xlrec;

			xlrec.xtime = time(NULL);
			xlrec.nrels = nrels;
			xlrec.nsubxacts = nchildren;
			rdata[0].data = (char *) (&xlrec);
			rdata[0].len = MinSizeOfXactCommit;
			rdata[0].buffer = InvalidBuffer;
			/* dump rels to delete */
			if (nrels > 0)
			{
				rdata[0].next = &(rdata[1]);
				rdata[1].data = (char *) rels;
				rdata[1].len = nrels * sizeof(RelFileNode);
				rdata[1].buffer = InvalidBuffer;
				lastrdata = 1;
			}
			/* dump committed child Xids */
			if (nchildren > 0)
			{
				rdata[lastrdata].next = &(rdata[2]);
				rdata[2].data = (char *) children;
				rdata[2].len = nchildren * sizeof(TransactionId);
				rdata[2].buffer = InvalidBuffer;
				lastrdata = 2;
			}
			rdata[lastrdata].next = NULL;

			recptr = XLogInsert(RM_XACT_ID, XLOG_XACT_COMMIT, rdata);
		}
		else
		{
			/* Just flush through last record written by me */
			recptr = ProcLastRecEnd;
		}

		/*
		 * We must flush our XLOG entries to disk if we made any XLOG entries,
		 * whether in or out of transaction control.  For example, if we
		 * reported a nextval() result to the client, this ensures that any
		 * XLOG record generated by nextval will hit the disk before we report
		 * the transaction committed.
		 *
		 * Note: if we generated a commit record above, MyXactMadeXLogEntry
		 * will certainly be set now.
		 */
		if (MyXactMadeXLogEntry)
		{
			/*
			 * Sleep before flush! So we can flush more than one commit
			 * records per single fsync.  (The idea is some other backend may
			 * do the XLogFlush while we're sleeping.  This needs work still,
			 * because on most Unixen, the minimum select() delay is 10msec or
			 * more, which is way too long.)
			 *
			 * We do not sleep if enableFsync is not turned on, nor if there
			 * are fewer than CommitSiblings other backends with active
			 * transactions.
			 */
			if (CommitDelay > 0 && enableFsync &&
				CountActiveBackends() >= CommitSiblings)
				pg_usleep(CommitDelay);

			XLogFlush(recptr);
		}

		/*
		 * We must mark the transaction committed in clog if its XID appears
		 * either in permanent rels or in local temporary rels. We test this
		 * by seeing if we made transaction-controlled entries *OR* local-rel
		 * tuple updates.  Note that if we made only the latter, we have not
		 * emitted an XLOG record for our commit, and so in the event of a
		 * crash the clog update might be lost.  This is okay because no one
		 * else will ever care whether we committed.
		 */
		if (madeTCentries || MyXactMadeTempRelUpdate)
		{
			TransactionIdCommit(xid);
			/* to avoid race conditions, the parent must commit first */
			TransactionIdCommitTree(nchildren, children);
		}

		/* Unlock checkpoint lock if we acquired it */
		if (madeTCentries)
			LWLockRelease(CheckpointStartLock);

		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);
}


/*
 *	AtCommit_LocalCache
 */
static void
AtCommit_LocalCache(void)
{
	/*
	 * Make catalog changes visible to me for the next command.
	 */
	CommandEndInvalidationMessages();
}

/*
 *	AtCommit_Memory
 */
static void
AtCommit_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);

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

/* ----------------------------------------------------------------
 *						CommitSubTransaction stuff
 * ----------------------------------------------------------------
 */

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

	Assert(s->parent != NULL);

	/* Return to parent transaction level's memory context. */
	CurTransactionContext = s->parent->curTransactionContext;
	MemoryContextSwitchTo(CurTransactionContext);

	/*
	 * Ordinarily we cannot throw away the child's CurTransactionContext,
	 * since the data it contains will be needed at upper commit.  However, if
	 * there isn't actually anything in it, we can throw it away.  This avoids
	 * a small memory leak in the common case of "trivial" subxacts.
	 */
	if (MemoryContextIsEmpty(s->curTransactionContext))
	{
		MemoryContextDelete(s->curTransactionContext);
		s->curTransactionContext = NULL;
	}
}

/*
 * AtSubCommit_childXids
 *
 * Pass my own XID and my child XIDs up to my parent as committed children.
 */
static void
AtSubCommit_childXids(void)
{
	TransactionState s = CurrentTransactionState;
	MemoryContext old_cxt;

	Assert(s->parent != NULL);

	/*
	 * We keep the child-XID lists in TopTransactionContext; this avoids
	 * setting up child-transaction contexts for what might be just a few
	 * bytes of grandchild XIDs.
	 */
	old_cxt = MemoryContextSwitchTo(TopTransactionContext);

	s->parent->childXids = lappend_xid(s->parent->childXids,
									   s->transactionId);

	if (s->childXids != NIL)
	{
		s->parent->childXids = list_concat(s->parent->childXids,
										   s->childXids);

		/*
		 * list_concat doesn't free the list header for the second list; do so
		 * here to avoid memory leakage (kluge)
		 */
		pfree(s->childXids);
		s->childXids = NIL;
	}

	MemoryContextSwitchTo(old_cxt);
}

/*
 * RecordSubTransactionCommit
 */
static void
RecordSubTransactionCommit(void)
{
	/*
	 * We do not log the subcommit in XLOG; it doesn't matter until the
	 * top-level transaction commits.
	 *
	 * We must mark the subtransaction subcommitted in clog if its XID appears
	 * either in permanent rels or in local temporary rels. We test this by
	 * seeing if we made transaction-controlled entries *OR* local-rel tuple
	 * updates.  (The test here actually covers the entire transaction tree so
	 * far, so it may mark subtransactions that don't really need it, but it's
	 * probably not worth being tenser. Note that if a prior subtransaction
	 * dirtied these variables, then RecordTransactionCommit will have to do
	 * the full pushup anyway...)
	 */
	if (MyLastRecPtr.xrecoff != 0 || MyXactMadeTempRelUpdate)
	{
		TransactionId xid = GetCurrentTransactionId();

		/* XXX does this really need to be a critical section? */
		START_CRIT_SECTION();

		/* Record subtransaction subcommit */
		TransactionIdSubCommit(xid);

		END_CRIT_SECTION();
	}
}

/* ----------------------------------------------------------------
 *						AbortTransaction stuff
 * ----------------------------------------------------------------
 */

/*
 *	RecordTransactionAbort
 */
static void
RecordTransactionAbort(void)
{
	int			nrels;
	RelFileNode *rels;
	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.)
	 */
	if (MyLastRecPtr.xrecoff != 0 || MyXactMadeTempRelUpdate || nrels > 0)
	{
		TransactionId xid = GetCurrentTransactionId();