transam.c

关系型数据库 Postgresql 6.5.2

 *
 *		Recovery checking is more difficult in the case where
 *		several backends are executing concurrently because the
 *		transactions may be executing in the other backends.
 *		So, we only do recovery stuff when the backend is explicitly
 *		passed a flag on the command line.
 * --------------------------------
 */
static void
TransRecover(Relation logRelation)
{
#ifdef NOT_USED
	/* ----------------
	 *	  first get the last recorded transaction in the log.
	 * ----------------
	 */
	TransGetLastRecordedTransaction(logRelation, logLastXid, &fail);
	if (fail == true)
		elog(ERROR, "TransRecover: failed TransGetLastRecordedTransaction");

	/* ----------------
	 *	  next get the "last" and "next" variables
	 * ----------------
	 */
	VariableRelationGetLastXid(&varLastXid);
	VariableRelationGetNextXid(&varNextXid);

	/* ----------------
	 *	  intregity test (1)
	 * ----------------
	 */
	if (TransactionIdIsLessThan(varNextXid, logLastXid))
		elog(ERROR, "TransRecover: varNextXid < logLastXid");

	/* ----------------
	 *	  intregity test (2)
	 * ----------------
	 */

	/* ----------------
	 *	  intregity test (3)
	 * ----------------
	 */

	/* ----------------
	 *	here we have a valid "
	 *
	 *			**** RESUME HERE ****
	 * ----------------
	 */
	varNextXid = TransactionIdDup(varLastXid);
	TransactionIdIncrement(&varNextXid);

	VarPut(var, VAR_PUT_LASTXID, varLastXid);
	VarPut(var, VAR_PUT_NEXTXID, varNextXid);
#endif
}

/* ----------------------------------------------------------------
 *						Interface functions
 *
 *		InitializeTransactionLog
 *		========
 *		   this function (called near cinit) initializes
 *		   the transaction log, time and variable relations.
 *
 *		TransactionId DidCommit
 *		TransactionId DidAbort
 *		TransactionId IsInProgress
 *		========
 *		   these functions test the transaction status of
 *		   a specified transaction id.
 *
 *		TransactionId Commit
 *		TransactionId Abort
 *		TransactionId SetInProgress
 *		========
 *		   these functions set the transaction status
 *		   of the specified xid. TransactionIdCommit() also
 *		   records the current time in the time relation
 *		   and updates the variable relation counter.
 *
 * ----------------------------------------------------------------
 */

/*
 * InitializeTransactionLog
 *		Initializes transaction logging.
 */
void
InitializeTransactionLog(void)
{
	Relation	logRelation;
	MemoryContext oldContext;

	/* ----------------
	 *	  don't do anything during bootstrapping
	 * ----------------
	 */
	if (AMI_OVERRIDE)
		return;

	/* ----------------
	 *	 disable the transaction system so the access methods
	 *	 don't interfere during initialization.
	 * ----------------
	 */
	OverrideTransactionSystem(true);

	/* ----------------
	 *	make sure allocations occur within the top memory context
	 *	so that our log management structures are protected from
	 *	garbage collection at the end of every transaction.
	 * ----------------
	 */
	oldContext = MemoryContextSwitchTo(TopMemoryContext);

	/* ----------------
	 *	 first open the log and time relations
	 *	 (these are created by amiint so they are guaranteed to exist)
	 * ----------------
	 */
	logRelation = heap_openr(LogRelationName);
	VariableRelation = heap_openr(VariableRelationName);
	/* ----------------
	 *	 XXX TransactionLogUpdate requires that LogRelation
	 *	 is valid so we temporarily set it so we can initialize
	 *	 things properly. This could be done cleaner.
	 * ----------------
	 */
	LogRelation = logRelation;

	/* ----------------
	 *	 if we have a virgin database, we initialize the log
	 *	 relation by committing the AmiTransactionId (id 512) and we
	 *	 initialize the variable relation by setting the next available
	 *	 transaction id to FirstTransactionId (id 514).  OID initialization
	 *	 happens as a side effect of bootstrapping in varsup.c.
	 * ----------------
	 */
	SpinAcquire(OidGenLockId);
	if (!TransactionIdDidCommit(AmiTransactionId))
	{

		/* ----------------
		 *	SOMEDAY initialize the information stored in
		 *			the headers of the log/variable relations.
		 * ----------------
		 */
		TransactionLogUpdate(AmiTransactionId, XID_COMMIT);
		TransactionIdStore(AmiTransactionId, &cachedTestXid);
		cachedTestXidStatus = XID_COMMIT;
		VariableRelationPutNextXid(FirstTransactionId);

	}
	else if (RecoveryCheckingEnabled())
	{
		/* ----------------
		 *		if we have a pre-initialized database and if the
		 *		perform recovery checking flag was passed then we
		 *		do our database integrity checking.
		 * ----------------
		 */
		TransRecover(logRelation);
	}
	LogRelation = (Relation) NULL;
	SpinRelease(OidGenLockId);

	/* ----------------
	 *	now re-enable the transaction system
	 * ----------------
	 */
	OverrideTransactionSystem(false);

	/* ----------------
	 *	instantiate the global variables
	 * ----------------
	 */
	LogRelation = logRelation;

	/* ----------------
	 *	restore the memory context to the previous context
	 *	before we return from initialization.
	 * ----------------
	 */
	MemoryContextSwitchTo(oldContext);
}

/* --------------------------------
 *		TransactionId DidCommit
 *		TransactionId DidAbort
 *		TransactionId IsInProgress
 * --------------------------------
 */

/*
 * TransactionIdDidCommit
 *		True iff transaction associated with the identifier did commit.
 *
 * Note:
 *		Assumes transaction identifier is valid.
 */
bool							/* true if given transaction committed */
TransactionIdDidCommit(TransactionId transactionId)
{
	if (AMI_OVERRIDE)
		return true;

	return TransactionLogTest(transactionId, XID_COMMIT);
}

/*
 * TransactionIdDidAborted
 *		True iff transaction associated with the identifier did abort.
 *
 * Note:
 *		Assumes transaction identifier is valid.
 *		XXX Is this unneeded?
 */
bool							/* true if given transaction aborted */
TransactionIdDidAbort(TransactionId transactionId)
{
	if (AMI_OVERRIDE)
		return false;

	return TransactionLogTest(transactionId, XID_ABORT);
}

/*
 * Now this func in shmem.c and gives quality answer by scanning
 * PROC structures of all running backend. - vadim 11/26/96
 *
 * Old comments:
 * true if given transaction neither committed nor aborted

bool
TransactionIdIsInProgress(TransactionId transactionId)
{
	if (AMI_OVERRIDE)
		return false;

	return TransactionLogTest(transactionId, XID_INPROGRESS);
}
 */

/* --------------------------------
 *		TransactionId Commit
 *		TransactionId Abort
 *		TransactionId SetInProgress
 * --------------------------------
 */

/*
 * TransactionIdCommit
 *		Commits the transaction associated with the identifier.
 *
 * Note:
 *		Assumes transaction identifier is valid.
 */
void
TransactionIdCommit(TransactionId transactionId)
{
	if (AMI_OVERRIDE)
		return;

	TransactionLogUpdate(transactionId, XID_COMMIT);
}

/*
 * TransactionIdAbort
 *		Aborts the transaction associated with the identifier.
 *
 * Note:
 *		Assumes transaction identifier is valid.
 */
void
TransactionIdAbort(TransactionId transactionId)
{
	if (AMI_OVERRIDE)
		return;

	TransactionLogUpdate(transactionId, XID_ABORT);
}