C++ TransactionIdPrecedes函数代码示例

/*
 * SubTransGetTopmostTransaction
 *
 * Returns the topmost transaction of the given transaction id.
 *
 * Because we cannot look back further than TransactionXmin, it is possible
 * that this function will lie and return an intermediate subtransaction ID
 * instead of the true topmost parent ID.  This is OK, because in practice
 * we only care about detecting whether the topmost parent is still running
 * or is part of a current snapshot's list of still-running transactions.
 * Therefore, any XID before TransactionXmin is as good as any other.
 */
TransactionId
SubTransGetTopmostTransaction(TransactionId xid)
{
	TransactionId parentXid = xid,
				previousXid = xid;

	/* Can't ask about stuff that might not be around anymore */
	Assert(TransactionIdFollowsOrEquals(xid, TransactionXmin));

	while (TransactionIdIsValid(parentXid))
	{
		previousXid = parentXid;
		if (TransactionIdPrecedes(parentXid, TransactionXmin))
			break;
		parentXid = SubTransGetParent(parentXid);

		/*
		 * By convention the parent xid gets allocated first, so should always
		 * precede the child xid. Anything else points to a corrupted data
		 * structure that could lead to an infinite loop, so exit.
		 */
		if (!TransactionIdPrecedes(parentXid, previousXid))
			elog(ERROR, "pg_subtrans contains invalid entry: xid %u points to parent xid %u",
				 previousXid, parentXid);
	}

	Assert(TransactionIdIsValid(previousXid));

	return previousXid;
}

/*
 * Get new XID. For global transaction is it previsly set by dtm_begin_transaction or dtm_join_transaction.
 * Local transactions are using range of local Xids obtains from DTM.
 */
static TransactionId DtmGetNextXid()
{
	TransactionId xid;
	LWLockAcquire(dtm->xidLock, LW_EXCLUSIVE);
	if (TransactionIdIsValid(DtmNextXid))
	{
		XTM_INFO("Use global XID %d\n", DtmNextXid);
		xid = DtmNextXid;

		if (TransactionIdPrecedesOrEquals(ShmemVariableCache->nextXid, xid))
		{
			/* Advance ShmemVariableCache->nextXid formward until new Xid */
			while (TransactionIdPrecedes(ShmemVariableCache->nextXid, xid))
			{
				XTM_INFO("Extend CLOG for global transaction to %d\n", ShmemVariableCache->nextXid);
				ExtendCLOG(ShmemVariableCache->nextXid);
				ExtendCommitTs(ShmemVariableCache->nextXid);
				ExtendSUBTRANS(ShmemVariableCache->nextXid);
				TransactionIdAdvance(ShmemVariableCache->nextXid);
			}
			dtm->nReservedXids = 0;
		}
	}
	else
	{
		if (dtm->nReservedXids == 0)
		{
            XTM_INFO("%d: reserve new XID range\n", getpid());
			dtm->nReservedXids = ArbiterReserve(ShmemVariableCache->nextXid, DtmLocalXidReserve, &dtm->nextXid);
			Assert(dtm->nReservedXids > 0);
			Assert(TransactionIdFollowsOrEquals(dtm->nextXid, ShmemVariableCache->nextXid));

			/* Advance ShmemVariableCache->nextXid formward until new Xid */
			while (TransactionIdPrecedes(ShmemVariableCache->nextXid, dtm->nextXid))
			{
				XTM_INFO("Extend CLOG for local transaction to %d\n", ShmemVariableCache->nextXid);
				ExtendCLOG(ShmemVariableCache->nextXid);
				ExtendCommitTs(ShmemVariableCache->nextXid);
				ExtendSUBTRANS(ShmemVariableCache->nextXid);
				TransactionIdAdvance(ShmemVariableCache->nextXid);
			}
		}
		Assert(ShmemVariableCache->nextXid == dtm->nextXid);
		xid = dtm->nextXid++;
		dtm->nReservedXids -= 1;
		XTM_INFO("Obtain new local XID %d\n", xid);
	}
	LWLockRelease(dtm->xidLock);
	return xid;
}

/*
 * Compute the oldest xmin across all slots and store it in the ProcArray.
 */
void
ReplicationSlotsComputeRequiredXmin(bool already_locked)
{
	int			i;
	TransactionId agg_xmin = InvalidTransactionId;
	TransactionId agg_catalog_xmin = InvalidTransactionId;

	Assert(ReplicationSlotCtl != NULL);

	if (!already_locked)
		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);

	for (i = 0; i < max_replication_slots; i++)
	{
		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
		TransactionId effective_xmin;
		TransactionId effective_catalog_xmin;

		if (!s->in_use)
			continue;

		{
			volatile ReplicationSlot *vslot = s;

			SpinLockAcquire(&s->mutex);
			effective_xmin = vslot->effective_xmin;
			effective_catalog_xmin = vslot->effective_catalog_xmin;
			SpinLockRelease(&s->mutex);
		}

		/* check the data xmin */
		if (TransactionIdIsValid(effective_xmin) &&
			(!TransactionIdIsValid(agg_xmin) ||
			 TransactionIdPrecedes(effective_xmin, agg_xmin)))
			agg_xmin = effective_xmin;

		/* check the catalog xmin */
		if (TransactionIdIsValid(effective_catalog_xmin) &&
			(!TransactionIdIsValid(agg_catalog_xmin) ||
			 TransactionIdPrecedes(effective_catalog_xmin, agg_catalog_xmin)))
			agg_catalog_xmin = effective_catalog_xmin;
	}

	if (!already_locked)
		LWLockRelease(ReplicationSlotControlLock);

	ProcArraySetReplicationSlotXmin(agg_xmin, agg_catalog_xmin, already_locked);
}

/*
 * do a TransactionId -> txid conversion for an XID near the given epoch
 */
static txid
convert_xid(TransactionId xid, const TxidEpoch *state)
{
#ifndef INT64_IS_BUSTED
	uint64		epoch;

	/* return special xid's as-is */
	if (!TransactionIdIsNormal(xid))
		return (txid) xid;

	/* xid can be on either side when near wrap-around */
	epoch = (uint64) state->epoch;
	if (xid > state->last_xid &&
		TransactionIdPrecedes(xid, state->last_xid))
		epoch--;
	else if (xid < state->last_xid &&
			 TransactionIdFollows(xid, state->last_xid))
		epoch++;

	return (epoch << 32) | xid;
#else							/* INT64_IS_BUSTED */
	/* we can't do anything with the epoch, so ignore it */
	return (txid) xid & MAX_TXID;
#endif   /* INT64_IS_BUSTED */
}

/*
 * Move forwards the oldest commitTS value that can be consulted
 */
void
AdvanceOldestCommitTsXid(TransactionId oldestXact)
{
	LWLockAcquire(CommitTsLock, LW_EXCLUSIVE);
	if (ShmemVariableCache->oldestCommitTsXid != InvalidTransactionId &&
	TransactionIdPrecedes(ShmemVariableCache->oldestCommitTsXid, oldestXact))
		ShmemVariableCache->oldestCommitTsXid = oldestXact;
	LWLockRelease(CommitTsLock);
}

/*
 * 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)
{
	XidStatus	xidstatus;

	xidstatus = TransactionLogFetch(transactionId);

	/*
	 * If it's marked committed, it's committed.
	 */
	if (xidstatus == TRANSACTION_STATUS_COMMITTED)
#ifdef PGXC
	{
		syncGXID_GTM((GlobalTransactionId)transactionId);
#endif
		return true;
#ifdef PGXC
	}
#endif

	/*
	 * If it's marked subcommitted, we have to check the parent recursively.
	 * However, if it's older than TransactionXmin, we can't look at
	 * pg_subtrans; instead assume that the parent crashed without cleaning up
	 * its children.
	 *
	 * Originally we Assert'ed that the result of SubTransGetParent was not
	 * zero. However with the introduction of prepared transactions, there can
	 * be a window just after database startup where we do not have complete
	 * knowledge in pg_subtrans of the transactions after TransactionXmin.
	 * StartupSUBTRANS() has ensured that any missing information will be
	 * zeroed.	Since this case should not happen under normal conditions, it
	 * seems reasonable to emit a WARNING for it.
	 */
	if (xidstatus == TRANSACTION_STATUS_SUB_COMMITTED)
	{
		TransactionId parentXid;

		if (TransactionIdPrecedes(transactionId, TransactionXmin))
			return false;
		parentXid = SubTransGetParent(transactionId);
		if (!TransactionIdIsValid(parentXid))
		{
			elog(WARNING, "no pg_subtrans entry for subcommitted XID %u",
				 transactionId);
			return false;
		}
		return TransactionIdDidCommit(parentXid);
	}

	/*
	 * It's not committed.
	 */
	return false;
}

/*
 * GetOldestXmin -- returns oldest transaction that was running
 *					when any current transaction was started.
 *
 * If allDbs is TRUE then all backends are considered; if allDbs is FALSE
 * then only backends running in my own database are considered.
 *
 * This is used by VACUUM to decide which deleted tuples must be preserved
 * in a table.	allDbs = TRUE is needed for shared relations, but allDbs =
 * FALSE is sufficient for non-shared relations, since only backends in my
 * own database could ever see the tuples in them.
 *
 * Note: we include the currently running xids in the set of considered xids.
 * This ensures that if a just-started xact has not yet set its snapshot,
 * when it does set the snapshot it cannot set xmin less than what we compute.
 */
TransactionId
GetOldestXmin(bool allDbs)
{
	SISeg	   *segP = shmInvalBuffer;
	ProcState  *stateP = segP->procState;
	TransactionId result;
	int			index;

	result = GetCurrentTransactionId();

	LWLockAcquire(SInvalLock, LW_SHARED);

	for (index = 0; index < segP->lastBackend; index++)
	{
		SHMEM_OFFSET pOffset = stateP[index].procStruct;

		if (pOffset != INVALID_OFFSET)
		{
			PGPROC	   *proc = (PGPROC *) MAKE_PTR(pOffset);

			if (allDbs || proc->databaseId == MyDatabaseId)
			{
				/* Fetch xid just once - see GetNewTransactionId */
				TransactionId xid = proc->xid;

				if (TransactionIdIsNormal(xid))
				{
					if (TransactionIdPrecedes(xid, result))
						result = xid;
					xid = proc->xmin;
					if (TransactionIdIsNormal(xid))
						if (TransactionIdPrecedes(xid, result))
							result = xid;
				}
			}
		}
	}

	LWLockRelease(SInvalLock);

	return result;
}

/*
 * Set the limit values between which commit TS can be consulted.
 */
void
SetCommitTsLimit(TransactionId oldestXact, TransactionId newestXact)
{
	/*
	 * Be careful not to overwrite values that are either further into the
	 * "future" or signal a disabled committs.
	 */
	LWLockAcquire(CommitTsLock, LW_EXCLUSIVE);
	if (ShmemVariableCache->oldestCommitTs != InvalidTransactionId)
	{
		if (TransactionIdPrecedes(ShmemVariableCache->oldestCommitTs, oldestXact))
			ShmemVariableCache->oldestCommitTs = oldestXact;
		if (TransactionIdPrecedes(newestXact, ShmemVariableCache->newestCommitTs))
			ShmemVariableCache->newestCommitTs = newestXact;
	}
	else
	{
		Assert(ShmemVariableCache->newestCommitTs == InvalidTransactionId);
	}
	LWLockRelease(CommitTsLock);
}

/* Record lowest soon-prunable XID */
static void
heap_prune_record_prunable(PruneState *prstate, TransactionId xid)
{
	/*
	 * This should exactly match the PageSetPrunable macro.  We can't store
	 * directly into the page header yet, so we update working state.
	 */
	Assert(TransactionIdIsNormal(xid));
	if (!TransactionIdIsValid(prstate->new_prune_xid) ||
		TransactionIdPrecedes(xid, prstate->new_prune_xid))
		prstate->new_prune_xid = xid;
}

/*
 * Comparison function for RegisteredSnapshots heap.  Snapshots are ordered
 * by xmin, so that the snapshot with smallest xmin is at the top.
 */
static int
xmin_cmp(const pairingheap_node *a, const pairingheap_node *b, void *arg)
{
	const SnapshotData *asnap = pairingheap_const_container(SnapshotData, ph_node, a);
	const SnapshotData *bsnap = pairingheap_const_container(SnapshotData, ph_node, b);

	if (TransactionIdPrecedes(asnap->xmin, bsnap->xmin))
		return 1;
	else if (TransactionIdFollows(asnap->xmin, bsnap->xmin))
		return -1;
	else
		return 0;
}

/*
 * Decide which of two SUBTRANS page numbers is "older" for truncation purposes.
 *
 * We need to use comparison of TransactionIds here in order to do the right
 * thing with wraparound XID arithmetic.  However, if we are asked about
 * page number zero, we don't want to hand InvalidTransactionId to
 * TransactionIdPrecedes: it'll get weird about permanent xact IDs.  So,
 * offset both xids by FirstNormalTransactionId to avoid that.
 */
static bool
SubTransPagePrecedes(int page1, int page2)
{
	TransactionId xid1;
	TransactionId xid2;

	xid1 = ((TransactionId) page1) * SUBTRANS_XACTS_PER_PAGE;
	xid1 += FirstNormalTransactionId;
	xid2 = ((TransactionId) page2) * SUBTRANS_XACTS_PER_PAGE;
	xid2 += FirstNormalTransactionId;

	return TransactionIdPrecedes(xid1, xid2);
}

/*
 * Decide which of two CLOG page numbers is "older" for truncation purposes.
 *
 * We need to use comparison of TransactionIds here in order to do the right
 * thing with wraparound XID arithmetic.  However, if we are asked about
 * page number zero, we don't want to hand InvalidTransactionId to
 * TransactionIdPrecedes: it'll get weird about permanent xact IDs.  So,
 * offset both xids by FirstNormalTransactionId to avoid that.
 */
static bool
CommitTsPagePrecedes(int page1, int page2)
{
	TransactionId xid1;
	TransactionId xid2;

	xid1 = ((TransactionId) page1) * COMMIT_TS_XACTS_PER_PAGE;
	xid1 += FirstNormalTransactionId;
	xid2 = ((TransactionId) page2) * COMMIT_TS_XACTS_PER_PAGE;
	xid2 += FirstNormalTransactionId;

	return TransactionIdPrecedes(xid1, xid2);
}

/*
 * Decide which of two DistributedLog page numbers is "older" for
 * truncation purposes.
 *
 * We need to use comparison of TransactionIds here in order to do the right
 * thing with wraparound XID arithmetic.  However, if we are asked about
 * page number zero, we don't want to hand InvalidTransactionId to
 * TransactionIdPrecedes: it'll get weird about permanent xact IDs.  So,
 * offset both xids by FirstNormalTransactionId to avoid that.
 */
static bool
DistributedLog_PagePrecedes(int page1, int page2)
{
	TransactionId xid1;
	TransactionId xid2;

	xid1 = ((TransactionId) page1) * ENTRIES_PER_PAGE;
	xid1 += FirstNormalTransactionId;
	xid2 = ((TransactionId) page2) * ENTRIES_PER_PAGE;
	xid2 += FirstNormalTransactionId;

	return TransactionIdPrecedes(xid1, xid2);
}

/*
 * Get oldest Xid visible by any active transaction (global or local)
 * Take in account global Xmin received from DTMD
 */
static TransactionId DtmGetOldestXmin(Relation rel, bool ignoreVacuum)
{
	TransactionId localXmin = PgGetOldestXmin(rel, ignoreVacuum);
	TransactionId globalXmin = dtm->minXid;
	XTM_INFO("XTM: DtmGetOldestXmin localXmin=%d, globalXmin=%d\n", localXmin, globalXmin);

	if (TransactionIdIsValid(globalXmin))
	{
		globalXmin -= vacuum_defer_cleanup_age;
		if (!TransactionIdIsNormal(globalXmin))
			globalXmin = FirstNormalTransactionId;
		if (TransactionIdPrecedes(globalXmin, localXmin))
			localXmin = globalXmin;
		XTM_INFO("XTM: DtmGetOldestXmin adjusted localXmin=%d, globalXmin=%d\n", localXmin, globalXmin);
	}
	return localXmin;
}

/*
 * HeapTupleIsSurelyDead
 *
 *	Determine whether a tuple is surely dead.  We sometimes use this
 *	in lieu of HeapTupleSatisifesVacuum when the tuple has just been
 *	tested by HeapTupleSatisfiesMVCC and, therefore, any hint bits that
 *	can be set should already be set.  We assume that if no hint bits
 *	either for xmin or xmax, the transaction is still running.  This is
 *	therefore faster than HeapTupleSatisfiesVacuum, because we don't
 *	consult CLOG (and also because we don't need to give an exact answer,
 *	just whether or not the tuple is surely dead).
 */
bool
HeapTupleIsSurelyDead(HeapTuple htup, TransactionId OldestXmin)
{
	HeapTupleHeader tuple = htup->t_data;

	Assert(ItemPointerIsValid(&htup->t_self));
	Assert(htup->t_tableOid != InvalidOid);

	/*
	 * If the inserting transaction is marked invalid, then it aborted, and
	 * the tuple is definitely dead.  If it's marked neither committed nor
	 * invalid, then we assume it's still alive (since the presumption is that
	 * all relevant hint bits were just set moments ago).
	 */
	if (!HeapTupleHeaderXminCommitted(tuple))
		return HeapTupleHeaderXminInvalid(tuple) ? true : false;

	/*
	 * If the inserting transaction committed, but any deleting transaction
	 * aborted, the tuple is still alive.
	 */
	if (tuple->t_infomask & HEAP_XMAX_INVALID)
		return false;

	/*
	 * If the XMAX is just a lock, the tuple is still alive.
	 */
	if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))
		return false;

	/*
	 * If the Xmax is a MultiXact, it might be dead or alive, but we cannot
	 * know without checking pg_multixact.
	 */
	if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
		return false;

	/* If deleter isn't known to have committed, assume it's still running. */
	if (!(tuple->t_infomask & HEAP_XMAX_COMMITTED))
		return false;

	/* Deleter committed, so tuple is dead if the XID is old enough. */
	return TransactionIdPrecedes(HeapTupleHeaderGetRawXmax(tuple), OldestXmin);
}