tqual.c

来自「postgresql8.3.4源码,开源数据库」· C语言 代码 · 共 1,436 行 · 第 1/3 页

				return false;	/* inserted after scan started */

			if (tuple->t_infomask & HEAP_XMAX_INVALID)	/* xid invalid */
				return true;

			if (tuple->t_infomask & HEAP_IS_LOCKED)		/* not deleter */
				return true;

			Assert(!(tuple->t_infomask & HEAP_XMAX_IS_MULTI));

			if (!TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetXmax(tuple)))
			{
				/* deleting subtransaction must have aborted */
				SetHintBits(tuple, buffer, HEAP_XMAX_INVALID,
							InvalidTransactionId);
				return true;
			}

			if (HeapTupleHeaderGetCmax(tuple) >= snapshot->curcid)
				return true;	/* deleted after scan started */
			else
				return false;	/* deleted before scan started */
		}
		else if (TransactionIdIsInProgress(HeapTupleHeaderGetXmin(tuple)))
			return false;
		else if (TransactionIdDidCommit(HeapTupleHeaderGetXmin(tuple)))
			SetHintBits(tuple, buffer, HEAP_XMIN_COMMITTED,
						HeapTupleHeaderGetXmin(tuple));
		else
		{
			/* it must have aborted or crashed */
			SetHintBits(tuple, buffer, HEAP_XMIN_INVALID,
						InvalidTransactionId);
			return false;
		}
	}

	/*
	 * By here, the inserting transaction has committed - have to check
	 * when...
	 */
	if (XidInMVCCSnapshot(HeapTupleHeaderGetXmin(tuple), snapshot))
		return false;			/* treat as still in progress */

	if (tuple->t_infomask & HEAP_XMAX_INVALID)	/* xid invalid or aborted */
		return true;

	if (tuple->t_infomask & HEAP_IS_LOCKED)
		return true;

	if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
	{
		/* MultiXacts are currently only allowed to lock tuples */
		Assert(tuple->t_infomask & HEAP_IS_LOCKED);
		return true;
	}

	if (!(tuple->t_infomask & HEAP_XMAX_COMMITTED))
	{
		if (TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetXmax(tuple)))
		{
			if (HeapTupleHeaderGetCmax(tuple) >= snapshot->curcid)
				return true;	/* deleted after scan started */
			else
				return false;	/* deleted before scan started */
		}

		if (TransactionIdIsInProgress(HeapTupleHeaderGetXmax(tuple)))
			return true;

		if (!TransactionIdDidCommit(HeapTupleHeaderGetXmax(tuple)))
		{
			/* it must have aborted or crashed */
			SetHintBits(tuple, buffer, HEAP_XMAX_INVALID,
						InvalidTransactionId);
			return true;
		}

		/* xmax transaction committed */
		SetHintBits(tuple, buffer, HEAP_XMAX_COMMITTED,
					HeapTupleHeaderGetXmax(tuple));
	}

	/*
	 * OK, the deleting transaction committed too ... but when?
	 */
	if (XidInMVCCSnapshot(HeapTupleHeaderGetXmax(tuple), snapshot))
		return true;			/* treat as still in progress */

	return false;
}


/*
 * HeapTupleSatisfiesVacuum
 *
 *	Determine the status of tuples for VACUUM purposes.  Here, what
 *	we mainly want to know is if a tuple is potentially visible to *any*
 *	running transaction.  If so, it can't be removed yet by VACUUM.
 *
 * OldestXmin is a cutoff XID (obtained from GetOldestXmin()).	Tuples
 * deleted by XIDs >= OldestXmin are deemed "recently dead"; they might
 * still be visible to some open transaction, so we can't remove them,
 * even if we see that the deleting transaction has committed.
 */
HTSV_Result
HeapTupleSatisfiesVacuum(HeapTupleHeader tuple, TransactionId OldestXmin,
						 Buffer buffer)
{
	/*
	 * Has inserting transaction committed?
	 *
	 * If the inserting transaction aborted, then the tuple was never visible
	 * to any other transaction, so we can delete it immediately.
	 */
	if (!(tuple->t_infomask & HEAP_XMIN_COMMITTED))
	{
		if (tuple->t_infomask & HEAP_XMIN_INVALID)
			return HEAPTUPLE_DEAD;
		else if (tuple->t_infomask & HEAP_MOVED_OFF)
		{
			TransactionId xvac = HeapTupleHeaderGetXvac(tuple);

			if (TransactionIdIsCurrentTransactionId(xvac))
				return HEAPTUPLE_DELETE_IN_PROGRESS;
			if (TransactionIdIsInProgress(xvac))
				return HEAPTUPLE_DELETE_IN_PROGRESS;
			if (TransactionIdDidCommit(xvac))
			{
				SetHintBits(tuple, buffer, HEAP_XMIN_INVALID,
							InvalidTransactionId);
				return HEAPTUPLE_DEAD;
			}
			SetHintBits(tuple, buffer, HEAP_XMIN_COMMITTED,
						InvalidTransactionId);
		}
		else if (tuple->t_infomask & HEAP_MOVED_IN)
		{
			TransactionId xvac = HeapTupleHeaderGetXvac(tuple);

			if (TransactionIdIsCurrentTransactionId(xvac))
				return HEAPTUPLE_INSERT_IN_PROGRESS;
			if (TransactionIdIsInProgress(xvac))
				return HEAPTUPLE_INSERT_IN_PROGRESS;
			if (TransactionIdDidCommit(xvac))
				SetHintBits(tuple, buffer, HEAP_XMIN_COMMITTED,
							InvalidTransactionId);
			else
			{
				SetHintBits(tuple, buffer, HEAP_XMIN_INVALID,
							InvalidTransactionId);
				return HEAPTUPLE_DEAD;
			}
		}
		else if (TransactionIdIsInProgress(HeapTupleHeaderGetXmin(tuple)))
		{
			if (tuple->t_infomask & HEAP_XMAX_INVALID)	/* xid invalid */
				return HEAPTUPLE_INSERT_IN_PROGRESS;
			if (tuple->t_infomask & HEAP_IS_LOCKED)
				return HEAPTUPLE_INSERT_IN_PROGRESS;
			/* inserted and then deleted by same xact */
			return HEAPTUPLE_DELETE_IN_PROGRESS;
		}
		else if (TransactionIdDidCommit(HeapTupleHeaderGetXmin(tuple)))
			SetHintBits(tuple, buffer, HEAP_XMIN_COMMITTED,
						HeapTupleHeaderGetXmin(tuple));
		else
		{
			/*
			 * Not in Progress, Not Committed, so either Aborted or crashed
			 */
			SetHintBits(tuple, buffer, HEAP_XMIN_INVALID,
						InvalidTransactionId);
			return HEAPTUPLE_DEAD;
		}

		/*
		 * At this point the xmin is known committed, but we might not have
		 * been able to set the hint bit yet; so we can no longer Assert that
		 * it's set.
		 */
	}

	/*
	 * Okay, the inserter committed, so it was good at some point.	Now what
	 * about the deleting transaction?
	 */
	if (tuple->t_infomask & HEAP_XMAX_INVALID)
		return HEAPTUPLE_LIVE;

	if (tuple->t_infomask & HEAP_IS_LOCKED)
	{
		/*
		 * "Deleting" xact really only locked it, so the tuple is live in any
		 * case.  However, we should make sure that either XMAX_COMMITTED or
		 * XMAX_INVALID gets set once the xact is gone, to reduce the costs of
		 * examining the tuple for future xacts.  Also, marking dead
		 * MultiXacts as invalid here provides defense against MultiXactId
		 * wraparound (see also comments in heap_freeze_tuple()).
		 */
		if (!(tuple->t_infomask & HEAP_XMAX_COMMITTED))
		{
			if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
			{
				if (MultiXactIdIsRunning(HeapTupleHeaderGetXmax(tuple)))
					return HEAPTUPLE_LIVE;
			}
			else
			{
				if (TransactionIdIsInProgress(HeapTupleHeaderGetXmax(tuple)))
					return HEAPTUPLE_LIVE;
			}

			/*
			 * We don't really care whether xmax did commit, abort or crash.
			 * We know that xmax did lock the tuple, but it did not and will
			 * never actually update it.
			 */
			SetHintBits(tuple, buffer, HEAP_XMAX_INVALID,
						InvalidTransactionId);
		}
		return HEAPTUPLE_LIVE;
	}

	if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
	{
		/* MultiXacts are currently only allowed to lock tuples */
		Assert(tuple->t_infomask & HEAP_IS_LOCKED);
		return HEAPTUPLE_LIVE;
	}

	if (!(tuple->t_infomask & HEAP_XMAX_COMMITTED))
	{
		if (TransactionIdIsInProgress(HeapTupleHeaderGetXmax(tuple)))
			return HEAPTUPLE_DELETE_IN_PROGRESS;
		else if (TransactionIdDidCommit(HeapTupleHeaderGetXmax(tuple)))
			SetHintBits(tuple, buffer, HEAP_XMAX_COMMITTED,
						HeapTupleHeaderGetXmax(tuple));
		else
		{
			/*
			 * Not in Progress, Not Committed, so either Aborted or crashed
			 */
			SetHintBits(tuple, buffer, HEAP_XMAX_INVALID,
						InvalidTransactionId);
			return HEAPTUPLE_LIVE;
		}

		/*
		 * At this point the xmax is known committed, but we might not have
		 * been able to set the hint bit yet; so we can no longer Assert that
		 * it's set.
		 */
	}

	/*
	 * Deleter committed, but check special cases.
	 */

	if (TransactionIdEquals(HeapTupleHeaderGetXmin(tuple),
							HeapTupleHeaderGetXmax(tuple)))
	{
		/*
		 * Inserter also deleted it, so it was never visible to anyone else.
		 * However, we can only remove it early if it's not an updated tuple;
		 * else its parent tuple is linking to it via t_ctid, and this tuple
		 * mustn't go away before the parent does.
		 */
		if (!(tuple->t_infomask & HEAP_UPDATED))
			return HEAPTUPLE_DEAD;
	}

	if (!TransactionIdPrecedes(HeapTupleHeaderGetXmax(tuple), OldestXmin))
	{
		/* deleting xact is too recent, tuple could still be visible */
		return HEAPTUPLE_RECENTLY_DEAD;
	}

	/* Otherwise, it's dead and removable */
	return HEAPTUPLE_DEAD;
}


/*
 * GetTransactionSnapshot
 *		Get the appropriate snapshot for a new query in a transaction.
 *
 * The SerializableSnapshot is the first one taken in a transaction.
 * In serializable mode we just use that one throughout the transaction.
 * In read-committed mode, we take a new snapshot each time we are called.
 *
 * Note that the return value points at static storage that will be modified
 * by future calls and by CommandCounterIncrement().  Callers should copy
 * the result with CopySnapshot() if it is to be used very long.
 */
Snapshot
GetTransactionSnapshot(void)
{
	/* First call in transaction? */
	if (SerializableSnapshot == NULL)
	{
		SerializableSnapshot = GetSnapshotData(&SerializableSnapshotData, true);
		return SerializableSnapshot;
	}

	if (IsXactIsoLevelSerializable)
		return SerializableSnapshot;

	LatestSnapshot = GetSnapshotData(&LatestSnapshotData, false);

	return LatestSnapshot;
}

/*
 * GetLatestSnapshot
 *		Get a snapshot that is up-to-date as of the current instant,
 *		even if we are executing in SERIALIZABLE mode.
 */
Snapshot
GetLatestSnapshot(void)
{
	/* Should not be first call in transaction */
	if (SerializableSnapshot == NULL)
		elog(ERROR, "no snapshot has been set");

	LatestSnapshot = GetSnapshotData(&LatestSnapshotData, false);

	return LatestSnapshot;
}

/*
 * CopySnapshot
 *		Copy the given snapshot.
 *
 * The copy is palloc'd in the current memory context.
 */
Snapshot
CopySnapshot(Snapshot snapshot)
{
	Snapshot	newsnap;
	Size		subxipoff;
	Size		size;

	/* We allocate any XID arrays needed in the same palloc block. */
	size = subxipoff = sizeof(SnapshotData) +
		snapshot->xcnt * sizeof(TransactionId);
	if (snapshot->subxcnt > 0)
		size += snapshot->subxcnt * sizeof(TransactionId);

	newsnap = (Snapshot) palloc(size);
	memcpy(newsnap, snapshot, sizeof(SnapshotData));

	/* setup XID array */
	if (snapshot->xcnt > 0)
	{
		newsnap->xip = (TransactionId *) (newsnap + 1);
		memcpy(newsnap->xip, snapshot->xip,
			   snapshot->xcnt * sizeof(TransactionId));
	}
	else
		newsnap->xip = NULL;

	/* setup subXID array */
	if (snapshot->subxcnt > 0)
	{
		newsnap->subxip = (TransactionId *) ((char *) newsnap + subxipoff);
		memcpy(newsnap->subxip, snapshot->subxip,
			   snapshot->subxcnt * sizeof(TransactionId));
	}
	else
		newsnap->subxip = NULL;

	return newsnap;
}

/*
 * FreeSnapshot
 *		Free a snapshot previously copied with CopySnapshot.
 *
 * This is currently identical to pfree, but is provided for cleanliness.
 *
 * Do *not* apply this to the results of GetTransactionSnapshot or
 * GetLatestSnapshot, since those are just static structs.
 */
void
FreeSnapshot(Snapshot snapshot)
{
	pfree(snapshot);
}

/*
 * FreeXactSnapshot
 *		Free snapshot(s) at end of transaction.
 */
void
FreeXactSnapshot(void)
{
	/*
	 * We do not free the xip arrays for the static snapshot structs; they
	 * will be reused soon. So this is now just a state change to prevent
	 * outside callers from accessing the snapshots.
	 */
	SerializableSnapshot = NULL;
	LatestSnapshot = NULL;
	ActiveSnapshot = NULL;		/* just for cleanliness */
}

/*
 * XidInMVCCSnapshot
 *		Is the given XID still-in-progress according to the snapshot?
 *
 * Note: GetSnapshotData never stores either top xid or subxids of our own
 * backend into a snapshot, so these xids will not be reported as "running"
 * by this function.  This is OK for current uses, because we actually only
 * apply this for known-committed XIDs.
 */
static bool
XidInMVCCSnapshot(TransactionId xid, Snapshot snapshot)
{
	uint32		i;

	/*
	 * Make a quick range check to eliminate most XIDs without looking at the
	 * xip arrays.	Note that this is OK even if we convert a subxact XID to
	 * its parent below, because a subxact with XID < xmin has surely also got
	 * a parent with XID < xmin, while one with XID >= xmax must belong to a
	 * parent that was not yet committed at the time of this snapshot.
	 */

	/* Any xid < xmin is not in-progress */
	if (TransactionIdPrecedes(xid, snapshot->xmin))
		return false;
	/* Any xid >= xmax is in-progress */
	if (TransactionIdFollowsOrEquals(xid, snapshot->xmax))
		return true;

	/*
	 * If the snapshot contains full subxact data, the fastest way to check
	 * things is just to compare the given XID against both subxact XIDs and
	 * top-level XIDs.	If the snapshot overflowed, we have to use pg_subtrans
	 * to convert a subxact XID to its parent XID, but then we need only look
	 * at top-level XIDs not subxacts.
	 */
	if (snapshot->subxcnt >= 0)
	{
		/* full data, so search subxip */
		int32		j;

		for (j = 0; j < snapshot->subxcnt; j++)
		{
			if (TransactionIdEquals(xid, snapshot->subxip[j]))
				return true;
		}

		/* not there, fall through to search xip[] */
	}
	else
	{
		/* overflowed, so convert xid to top-level */
		xid = SubTransGetTopmostTransaction(xid);

		/*
		 * If xid was indeed a subxact, we might now have an xid < xmin, so
		 * recheck to avoid an array scan.	No point in rechecking xmax.
		 */
		if (TransactionIdPrecedes(xid, snapshot->xmin))
			return false;
	}

	for (i = 0; i < snapshot->xcnt; i++)
	{
		if (TransactionIdEquals(xid, snapshot->xip[i]))
			return true;
	}

	return false;
}