access/heap/heapam_visibility.c

/*-------------------------------------------------------------------------
 *
 * heapam_visibility.c
 *	  Tuple visibility rules for tuples stored in heap.
 *
 * NOTE: all the HeapTupleSatisfies routines will update the tuple's
 * "hint" status bits if we see that the inserting or deleting transaction
 * has now committed or aborted (and it is safe to set the hint bits).
 * If the hint bits are changed, MarkBufferDirtyHint is called on
 * the passed-in buffer.  The caller must hold not only a pin, but at least
 * shared buffer content lock on the buffer containing the tuple.
 *
 * NOTE: When using a non-MVCC snapshot, we must check
 * TransactionIdIsInProgress (which looks in the PGXACT array)
 * before TransactionIdDidCommit/TransactionIdDidAbort (which look in
 * pg_xact).  Otherwise we have a race condition: we might decide that a
 * just-committed transaction crashed, because none of the tests succeed.
 * xact.c is careful to record commit/abort in pg_xact before it unsets
 * MyPgXact->xid in the PGXACT array.  That fixes that problem, but it
 * also means there is a window where TransactionIdIsInProgress and
 * TransactionIdDidCommit will both return true.  If we check only
 * TransactionIdDidCommit, we could consider a tuple committed when a
 * later GetSnapshotData call will still think the originating transaction
 * is in progress, which leads to application-level inconsistency.  The
 * upshot is that we gotta check TransactionIdIsInProgress first in all
 * code paths, except for a few cases where we are looking at
 * subtransactions of our own main transaction and so there can't be any
 * race condition.
 *
 * When using an MVCC snapshot, we rely on XidInMVCCSnapshot rather than
 * TransactionIdIsInProgress, but the logic is otherwise the same: do not
 * check pg_xact until after deciding that the xact is no longer in progress.
 *
 *
 * Summary of visibility functions:
 *
 *	 HeapTupleSatisfiesMVCC()
 *		  visible to supplied snapshot, excludes current command
 *	 HeapTupleSatisfiesUpdate()
 *		  visible to instant snapshot, with user-supplied command
 *		  counter and more complex result
 *	 HeapTupleSatisfiesSelf()
 *		  visible to instant snapshot and current command
 *	 HeapTupleSatisfiesDirty()
 *		  like HeapTupleSatisfiesSelf(), but includes open transactions
 *	 HeapTupleSatisfiesVacuum()
 *		  visible to any running transaction, used by VACUUM
 *	 HeapTupleSatisfiesNonVacuumable()
 *		  Snapshot-style API for HeapTupleSatisfiesVacuum
 *	 HeapTupleSatisfiesToast()
 *		  visible unless part of interrupted vacuum, used for TOAST
 *	 HeapTupleSatisfiesAny()
 *		  all tuples are visible
 *
 * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *	  src/backend/access/heap/heapam_visibility.c
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "access/heapam.h"
#include "access/htup_details.h"
#include "access/multixact.h"
#include "access/subtrans.h"
#include "access/tableam.h"
#include "access/transam.h"
#include "access/xact.h"
#include "access/xlog.h"
#include "storage/bufmgr.h"
#include "storage/procarray.h"
#include "utils/builtins.h"
#include "utils/combocid.h"
#include "utils/snapmgr.h"


/*
 * SetHintBits()
 *
 * Set commit/abort hint bits on a tuple, if appropriate at this time.
 *
 * It is only safe to set a transaction-committed hint bit if we know the
 * transaction's commit record is guaranteed to be flushed to disk before the
 * buffer, or if the table is temporary or unlogged and will be obliterated by
 * a crash anyway.  We cannot change the LSN of the page here, because we may
 * hold only a share lock on the buffer, so we can only use the LSN to
 * interlock this if the buffer's LSN already is newer than the commit LSN;
 * otherwise we have to just refrain from setting the hint bit until some
 * future re-examination of the tuple.
 *
 * We can always set hint bits when marking a transaction aborted.  (Some
 * code in heapam.c relies on that!)
 *
 * Also, if we are cleaning up HEAP_MOVED_IN or HEAP_MOVED_OFF entries, then
 * we can always set the hint bits, since pre-9.0 VACUUM FULL always used
 * synchronous commits and didn't move tuples that weren't previously
 * hinted.  (This is not known by this subroutine, but is applied by its
 * callers.)  Note: old-style VACUUM FULL is gone, but we have to keep this
 * module's support for MOVED_OFF/MOVED_IN flag bits for as long as we
 * support in-place update from pre-9.0 databases.
 *
 * Normal commits may be asynchronous, so for those we need to get the LSN
 * of the transaction and then check whether this is flushed.
 *
 * The caller should pass xid as the XID of the transaction to check, or
 * InvalidTransactionId if no check is needed.
 */
static inline void
SetHintBits(HeapTupleHeader tuple, Buffer buffer,
			uint16 infomask, TransactionId xid)
{
	if (TransactionIdIsValid(xid))
	{
		/* NB: xid must be known committed here! */
		XLogRecPtr	commitLSN = TransactionIdGetCommitLSN(xid);

		if (BufferIsPermanent(buffer) && XLogNeedsFlush(commitLSN) &&
			BufferGetLSNAtomic(buffer) < commitLSN)
		{
			/* not flushed and no LSN interlock, so don't set hint */
			return;
		}
	}

	tuple->t_infomask |= infomask;
	MarkBufferDirtyHint(buffer, true);
}

/*
 * HeapTupleSetHintBits --- exported version of SetHintBits()
 *
 * This must be separate because of C99's brain-dead notions about how to
 * implement inline functions.
 */
void
HeapTupleSetHintBits(HeapTupleHeader tuple, Buffer buffer,
					 uint16 infomask, TransactionId xid)
{
	SetHintBits(tuple, buffer, infomask, xid);
}


/*
 * HeapTupleSatisfiesSelf
 *		True iff heap tuple is valid "for itself".
 *
 * See SNAPSHOT_MVCC's definition for the intended behaviour.
 *
 * Note:
 *		Assumes heap tuple is valid.
 *
 * The satisfaction of "itself" requires the following:
 *
 * ((Xmin == my-transaction &&				the row was updated by the current transaction, and
 *		(Xmax is null						it was not deleted
 *		 [|| Xmax != my-transaction)])			[or it was deleted by another transaction]
 * ||
 *
 * (Xmin is committed &&					the row was modified by a committed transaction, and
 *		(Xmax is null ||					the row has not been deleted, or
 *			(Xmax != my-transaction &&			the row was deleted by another transaction
 *			 Xmax is not committed)))			that has not been committed
 */
static bool
HeapTupleSatisfiesSelf(HeapTuple htup, Snapshot snapshot, Buffer buffer)
{
	HeapTupleHeader tuple = htup->t_data;

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

	if (!HeapTupleHeaderXminCommitted(tuple))
	{
		if (HeapTupleHeaderXminInvalid(tuple))
			return false;

		/* Used by pre-9.0 binary upgrades */
		if (tuple->t_infomask & HEAP_MOVED_OFF)
		{
			TransactionId xvac = HeapTupleHeaderGetXvac(tuple);

			if (TransactionIdIsCurrentTransactionId(xvac))
				return false;
			if (!TransactionIdIsInProgress(xvac))
			{
				if (TransactionIdDidCommit(xvac))
				{
					SetHintBits(tuple, buffer, HEAP_XMIN_INVALID,
								InvalidTransactionId);
					return false;
				}
				SetHintBits(tuple, buffer, HEAP_XMIN_COMMITTED,
							InvalidTransactionId);
			}
		}
		/* Used by pre-9.0 binary upgrades */
		else if (tuple->t_infomask & HEAP_MOVED_IN)
		{
			TransactionId xvac = HeapTupleHeaderGetXvac(tuple);

			if (!TransactionIdIsCurrentTransactionId(xvac))
			{
				if (TransactionIdIsInProgress(xvac))
					return false;
				if (TransactionIdDidCommit(xvac))
					SetHintBits(tuple, buffer, HEAP_XMIN_COMMITTED,
								InvalidTransactionId);
				else
				{
					SetHintBits(tuple, buffer, HEAP_XMIN_INVALID,
								InvalidTransactionId);
					return false;
				}
			}
		}
		else if (TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetRawXmin(tuple)))
		{
			if (tuple->t_infomask & HEAP_XMAX_INVALID)	/* xid invalid */
				return true;

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

			if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
			{
				TransactionId xmax;

				xmax = HeapTupleGetUpdateXid(tuple);

				/* not LOCKED_ONLY, so it has to have an xmax */
				Assert(TransactionIdIsValid(xmax));

				/* updating subtransaction must have aborted */
				if (!TransactionIdIsCurrentTransactionId(xmax))
					return true;
				else
					return false;
			}

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

			return false;
		}
		else if (TransactionIdIsInProgress(HeapTupleHeaderGetRawXmin(tuple)))
			return false;
		else if (TransactionIdDidCommit(HeapTupleHeaderGetRawXmin(tuple)))
			SetHintBits(tuple, buffer, HEAP_XMIN_COMMITTED,
						HeapTupleHeaderGetRawXmin(tuple));
		else
		{
			/* it must have aborted or crashed */
			SetHintBits(tuple, buffer, HEAP_XMIN_INVALID,
						InvalidTransactionId);
			return false;
		}
	}

	/* by here, the inserting transaction has committed */

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

	if (tuple->t_infomask & HEAP_XMAX_COMMITTED)
	{
		if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))
			return true;
		return false;			/* updated by other */
	}

	if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
	{
		TransactionId xmax;

		if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))
			return true;

		xmax = HeapTupleGetUpdateXid(tuple);

		/* not LOCKED_ONLY, so it has to have an xmax */
		Assert(TransactionIdIsValid(xmax));

		if (TransactionIdIsCurrentTransactionId(xmax))
			return false;
		if (TransactionIdIsInProgress(xmax))
			return true;
		if (TransactionIdDidCommit(xmax))
			return false;
		/* it must have aborted or crashed */
		return true;
	}

	if (TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetRawXmax(tuple)))
	{
		if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))
			return true;
		return false;
	}

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

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

	/* xmax transaction committed */

	if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))
	{
		SetHintBits(tuple, buffer, HEAP_XMAX_INVALID,
					InvalidTransactionId);
		return true;
	}

	SetHintBits(tuple, buffer, HEAP_XMAX_COMMITTED,
				HeapTupleHeaderGetRawXmax(tuple));
	return false;
}

/*
 * HeapTupleSatisfiesAny
 *		Dummy "satisfies" routine: any tuple satisfies SnapshotAny.
 */
static bool
HeapTupleSatisfiesAny(HeapTuple htup, Snapshot snapshot, Buffer buffer)
{
	return true;
}

/*
 * HeapTupleSatisfiesToast
 *		True iff heap tuple is valid as a TOAST row.
 *
 * See SNAPSHOT_TOAST's definition for the intended behaviour.
 *
 * This is a simplified version that only checks for VACUUM moving conditions.
 * It's appropriate for TOAST usage because TOAST really doesn't want to do
 * its own time qual checks; if you can see the main table row that contains
 * a TOAST reference, you should be able to see the TOASTed value.  However,
 * vacuuming a TOAST table is independent of the main table, and in case such
 * a vacuum fails partway through, we'd better do this much checking.
 *
 * Among other things, this means you can't do UPDATEs of rows in a TOAST
 * table.
 */
static bool
HeapTupleSatisfiesToast(HeapTuple htup, Snapshot snapshot,
						Buffer buffer)
{
	HeapTupleHeader tuple = htup->t_data;

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

	if (!HeapTupleHeaderXminCommitted(tuple))
	{
		if (HeapTupleHeaderXminInvalid(tuple))
			return false;

		/* Used by pre-9.0 binary upgrades */
		if (tuple->t_infomask & HEAP_MOVED_OFF)
		{
			TransactionId xvac = HeapTupleHeaderGetXvac(tuple);

			if (TransactionIdIsCurrentTransactionId(xvac))
				return false;
			if (!TransactionIdIsInProgress(xvac))
			{
				if (TransactionIdDidCommit(xvac))
				{
					SetHintBits(tuple, buffer, HEAP_XMIN_INVALID,
								InvalidTransactionId);
					return false;
				}
				SetHintBits(tuple, buffer, HEAP_XMIN_COMMITTED,
							InvalidTransactionId);
			}
		}
		/* Used by pre-9.0 binary upgrades */
		else if (tuple->t_infomask & HEAP_MOVED_IN)
		{
			TransactionId xvac = HeapTupleHeaderGetXvac(tuple);

			if (!TransactionIdIsCurrentTransactionId(xvac))
			{
				if (TransactionIdIsInProgress(xvac))
					return false;
				if (TransactionIdDidCommit(xvac))
					SetHintBits(tuple, buffer, HEAP_XMIN_COMMITTED,
								InvalidTransactionId);
				else
				{
					SetHintBits(tuple, buffer, HEAP_XMIN_INVALID,
								InvalidTransactionId);
					return false;
				}
			}
		}

		/*
		 * An invalid Xmin can be left behind by a speculative insertion that
		 * is canceled by super-deleting the tuple.  This also applies to
		 * TOAST tuples created during speculative insertion.
		 */
		else if (!TransactionIdIsValid(HeapTupleHeaderGetXmin(tuple)))
			return false;
	}

	/* otherwise assume the tuple is valid for TOAST. */
	return true;
}

/*
 * HeapTupleSatisfiesUpdate
 *
 *	This function returns a more detailed result code than most of the
 *	functions in this file, since UPDATE needs to know more than "is it
 *	visible?".  It also allows for user-supplied CommandId rather than
 *	relying on CurrentCommandId.
 *
 *	The possible return codes are:
 *
 *	TM_Invisible: the tuple didn't exist at all when the scan started, e.g. it
 *	was created by a later CommandId.
 *
 *	TM_Ok: The tuple is valid and visible, so it may be updated.
 *
 *	TM_SelfModified: The tuple was updated by the current transaction, after
 *	the current scan started.
 *
 *	TM_Updated: The tuple was updated by a committed transaction (including
 *	the case where the tuple was moved into a different partition).
 *
 *	TM_Deleted: The tuple was deleted by a committed transaction.
 *
 *	TM_BeingModified: The tuple is being updated by an in-progress transaction
 *	other than the current transaction.  (Note: this includes the case where
 *	the tuple is share-locked by a MultiXact, even if the MultiXact includes
 *	the current transaction.  Callers that want to distinguish that case must
 *	test for it themselves.)
 */
TM_Result
HeapTupleSatisfiesUpdate(HeapTuple htup, CommandId curcid,
						 Buffer buffer)
{
	HeapTupleHeader tuple = htup->t_data;

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

	if (!HeapTupleHeaderXminCommitted(tuple))
	{
		if (HeapTupleHeaderXminInvalid(tuple))
			return TM_Invisible;

		/* Used by pre-9.0 binary upgrades */
		if (tuple->t_infomask & HEAP_MOVED_OFF)
		{
			TransactionId xvac = HeapTupleHeaderGetXvac(tuple);

			if (TransactionIdIsCurrentTransactionId(xvac))
				return TM_Invisible;
			if (!TransactionIdIsInProgress(xvac))
			{
				if (TransactionIdDidCommit(xvac))
				{
					SetHintBits(tuple, buffer, HEAP_XMIN_INVALID,
								InvalidTransactionId);
					return TM_Invisible;
				}
				SetHintBits(tuple, buffer, HEAP_XMIN_COMMITTED,
							InvalidTransactionId);
			}
		}
		/* Used by pre-9.0 binary upgrades */
		else if (tuple->t_infomask & HEAP_MOVED_IN)
		{
			TransactionId xvac = HeapTupleHeaderGetXvac(tuple);

			if (!TransactionIdIsCurrentTransactionId(xvac))
			{
				if (TransactionIdIsInProgress(xvac))
					return TM_Invisible;
				if (TransactionIdDidCommit(xvac))
					SetHintBits(tuple, buffer, HEAP_XMIN_COMMITTED,
								InvalidTransactionId);
				else
				{
					SetHintBits(tuple, buffer, HEAP_XMIN_INVALID,
								InvalidTransactionId);
					return TM_Invisible;
				}
			}
		}
		else if (TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetRawXmin(tuple)))
		{
			if (HeapTupleHeaderGetCmin(tuple) >= curcid)
				return TM_Invisible;	/* inserted after scan started */

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

			if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))
			{
				TransactionId xmax;

				xmax = HeapTupleHeaderGetRawXmax(tuple);

				/*
				 * Careful here: even though this tuple was created by our own
				 * transaction, it might be locked by other transactions, if
				 * the original version was key-share locked when we updated
				 * it.
				 */

				if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
				{
					if (MultiXactIdIsRunning(xmax, true))
						return TM_BeingModified;
					else
						return TM_Ok;
				}

				/*
				 * If the locker is gone, then there is nothing of interest
				 * left in this Xmax; otherwise, report the tuple as
				 * locked/updated.
				 */
				if (!TransactionIdIsInProgress(xmax))
					return TM_Ok;
				return TM_BeingModified;
			}

			if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
			{
				TransactionId xmax;

				xmax = HeapTupleGetUpdateXid(tuple);

				/* not LOCKED_ONLY, so it has to have an xmax */
				Assert(TransactionIdIsValid(xmax));

				/* deleting subtransaction must have aborted */
				if (!TransactionIdIsCurrentTransactionId(xmax))
				{
					if (MultiXactIdIsRunning(HeapTupleHeaderGetRawXmax(tuple),
											 false))
						return TM_BeingModified;
					return TM_Ok;
				}
				else
				{
					if (HeapTupleHeaderGetCmax(tuple) >= curcid)
						return TM_SelfModified; /* updated after scan started */
					else
						return TM_Invisible;	/* updated before scan started */
				}
			}

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

			if (HeapTupleHeaderGetCmax(tuple) >= curcid)
				return TM_SelfModified; /* updated after scan started */
			else
				return TM_Invisible;	/* updated before scan started */
		}
		else if (TransactionIdIsInProgress(HeapTupleHeaderGetRawXmin(tuple)))
			return TM_Invisible;
		else if (TransactionIdDidCommit(HeapTupleHeaderGetRawXmin(tuple)))
			SetHintBits(tuple, buffer, HEAP_XMIN_COMMITTED,
						HeapTupleHeaderGetRawXmin(tuple));
		else
		{
			/* it must have aborted or crashed */
			SetHintBits(tuple, buffer, HEAP_XMIN_INVALID,
						InvalidTransactionId);
			return TM_Invisible;
		}
	}

	/* by here, the inserting transaction has committed */

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

	if (tuple->t_infomask & HEAP_XMAX_COMMITTED)
	{
		if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))
			return TM_Ok;
		if (!ItemPointerEquals(&htup->t_self, &tuple->t_ctid) ||
			HeapTupleHeaderIndicatesMovedPartitions(tuple))
			return TM_Updated;	/* updated by other */
		else
			return TM_Deleted;	/* deleted by other */
	}

	if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
	{
		TransactionId xmax;

		if (HEAP_LOCKED_UPGRADED(tuple->t_infomask))
			return TM_Ok;

		if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))
		{
			if (MultiXactIdIsRunning(HeapTupleHeaderGetRawXmax(tuple), true))
				return TM_BeingModified;

			SetHintBits(tuple, buffer, HEAP_XMAX_INVALID, InvalidTransactionId);
			return TM_Ok;
		}

		xmax = HeapTupleGetUpdateXid(tuple);
		if (!TransactionIdIsValid(xmax))
		{
			if (MultiXactIdIsRunning(HeapTupleHeaderGetRawXmax(tuple), false))
				return TM_BeingModified;
		}

		/* not LOCKED_ONLY, so it has to have an xmax */
		Assert(TransactionIdIsValid(xmax));

		if (TransactionIdIsCurrentTransactionId(xmax))
		{
			if (HeapTupleHeaderGetCmax(tuple) >= curcid)
				return TM_SelfModified; /* updated after scan started */
			else
				return TM_Invisible;	/* updated before scan started */
		}

		if (MultiXactIdIsRunning(HeapTupleHeaderGetRawXmax(tuple), false))
			return TM_BeingModified;

		if (TransactionIdDidCommit(xmax))
		{
			if (!ItemPointerEquals(&htup->t_self, &tuple->t_ctid) ||
				HeapTupleHeaderIndicatesMovedPartitions(tuple))
				return TM_Updated;
			else
				return TM_Deleted;
		}

		/*
		 * By here, the update in the Xmax is either aborted or crashed, but
		 * what about the other members?
		 */

		if (!MultiXactIdIsRunning(HeapTupleHeaderGetRawXmax(tuple), false))
		{
			/*
			 * There's no member, even just a locker, alive anymore, so we can
			 * mark the Xmax as invalid.
			 */
			SetHintBits(tuple, buffer, HEAP_XMAX_INVALID,
						InvalidTransactionId);
			return TM_Ok;
		}
		else
		{
			/* There are lockers running */
			return TM_BeingModified;
		}
	}

	if (TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetRawXmax(tuple)))
	{
		if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))
			return TM_BeingModified;
		if (HeapTupleHeaderGetCmax(tuple) >= curcid)
			return TM_SelfModified; /* updated after scan started */
		else
			return TM_Invisible;	/* updated before scan started */
	}

	if (TransactionIdIsInProgress(HeapTupleHeaderGetRawXmax(tuple)))
		return TM_BeingModified;

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

	/* xmax transaction committed */

	if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))
	{
		SetHintBits(tuple, buffer, HEAP_XMAX_INVALID,
					InvalidTransactionId);
		return TM_Ok;
	}

	SetHintBits(tuple, buffer, HEAP_XMAX_COMMITTED,
				HeapTupleHeaderGetRawXmax(tuple));
	if (!ItemPointerEquals(&htup->t_self, &tuple->t_ctid) ||
		HeapTupleHeaderIndicatesMovedPartitions(tuple))
		return TM_Updated;		/* updated by other */
	else
		return TM_Deleted;		/* deleted by other */
}

/*
 * HeapTupleSatisfiesDirty
 *		True iff heap tuple is valid including effects of open transactions.
 *
 * See SNAPSHOT_DIRTY's definition for the intended behaviour.
 *
 * This is essentially like HeapTupleSatisfiesSelf as far as effects of
 * the current transaction and committed/aborted xacts are concerned.
 * However, we also include the effects of other xacts still in progress.
 *
 * A special hack is that the passed-in snapshot struct is used as an
 * output argument to return the xids of concurrent xacts that affected the
 * tuple.  snapshot->xmin is set to the tuple's xmin if that is another
 * transaction that's still in progress; or to InvalidTransactionId if the
 * tuple's xmin is committed good, committed dead, or my own xact.
 * Similarly for snapshot->xmax and the tuple's xmax.  If the tuple was
 * inserted speculatively, meaning that the inserter might still back down
 * on the insertion without aborting the whole transaction, the associated
 * token is also returned in snapshot->speculativeToken.
 */
static bool
HeapTupleSatisfiesDirty(HeapTuple htup, Snapshot snapshot,
						Buffer buffer)
{
	HeapTupleHeader tuple = htup->t_data;

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

	snapshot->xmin = snapshot->xmax = InvalidTransactionId;
	snapshot->speculativeToken = 0;

	if (!HeapTupleHeaderXminCommitted(tuple))
	{
		if (HeapTupleHeaderXminInvalid(tuple))
			return false;

		/* Used by pre-9.0 binary upgrades */
		if (tuple->t_infomask & HEAP_MOVED_OFF)
		{
			TransactionId xvac = HeapTupleHeaderGetXvac(tuple);

			if (TransactionIdIsCurrentTransactionId(xvac))
				return false;
			if (!TransactionIdIsInProgress(xvac))
			{
				if (TransactionIdDidCommit(xvac))
				{
					SetHintBits(tuple, buffer, HEAP_XMIN_INVALID,
								InvalidTransactionId);
					return false;
				}
				SetHintBits(tuple, buffer, HEAP_XMIN_COMMITTED,
							InvalidTransactionId);
			}
		}
		/* Used by pre-9.0 binary upgrades */
		else if (tuple->t_infomask & HEAP_MOVED_IN)
		{
			TransactionId xvac = HeapTupleHeaderGetXvac(tuple);

			if (!TransactionIdIsCurrentTransactionId(xvac))
			{
				if (TransactionIdIsInProgress(xvac))
					return false;
				if (TransactionIdDidCommit(xvac))
					SetHintBits(tuple, buffer, HEAP_XMIN_COMMITTED,
								InvalidTransactionId);
				else
				{
					SetHintBits(tuple, buffer, HEAP_XMIN_INVALID,
								InvalidTransactionId);
					return false;
				}
			}
		}
		else if (TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetRawXmin(tuple)))
		{
			if (tuple->t_infomask & HEAP_XMAX_INVALID)	/* xid invalid */
				return true;

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

			if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
			{
				TransactionId xmax;

				xmax = HeapTupleGetUpdateXid(tuple);

				/* not LOCKED_ONLY, so it has to have an xmax */
				Assert(TransactionIdIsValid(xmax));

				/* updating subtransaction must have aborted */
				if (!TransactionIdIsCurrentTransactionId(xmax))
					return true;
				else
					return false;
			}

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

			return false;
		}
		else if (TransactionIdIsInProgress(HeapTupleHeaderGetRawXmin(tuple)))
		{
			/*
			 * Return the speculative token to caller.  Caller can worry about
			 * xmax, since it requires a conclusively locked row version, and
			 * a concurrent update to this tuple is a conflict of its
			 * purposes.
			 */
			if (HeapTupleHeaderIsSpeculative(tuple))
			{
				snapshot->speculativeToken =
					HeapTupleHeaderGetSpeculativeToken(tuple);

				Assert(snapshot->speculativeToken != 0);
			}

			snapshot->xmin = HeapTupleHeaderGetRawXmin(tuple);
			/* XXX shouldn't we fall through to look at xmax? */
			return true;		/* in insertion by other */
		}
		else if (TransactionIdDidCommit(HeapTupleHeaderGetRawXmin(tuple)))
			SetHintBits(tuple, buffer, HEAP_XMIN_COMMITTED,
						HeapTupleHeaderGetRawXmin(tuple));
		else
		{
			/* it must have aborted or crashed */
			SetHintBits(tuple, buffer, HEAP_XMIN_INVALID,
						InvalidTransactionId);
			return false;
		}
	}

	/* by here, the inserting transaction has committed */

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

	if (tuple->t_infomask & HEAP_XMAX_COMMITTED)
	{
		if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))
			return true;
		return false;			/* updated by other */
	}

	if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
	{
		TransactionId xmax;

		if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))
			return true;

		xmax = HeapTupleGetUpdateXid(tuple);

		/* not LOCKED_ONLY, so it has to have an xmax */
		Assert(TransactionIdIsValid(xmax));

		if (TransactionIdIsCurrentTransactionId(xmax))
			return false;
		if (TransactionIdIsInProgress(xmax))
		{
			snapshot->xmax = xmax;
			return true;
		}
		if (TransactionIdDidCommit(xmax))
			return false;
		/* it must have aborted or crashed */
		return true;
	}

	if (TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetRawXmax(tuple)))
	{
		if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))
			return true;
		return false;
	}

	if (TransactionIdIsInProgress(HeapTupleHeaderGetRawXmax(tuple)))
	{
		if (!HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))
			snapshot->xmax = HeapTupleHeaderGetRawXmax(tuple);
		return true;
	}

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

	/* xmax transaction committed */

	if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))
	{
		SetHintBits(tuple, buffer, HEAP_XMAX_INVALID,
					InvalidTransactionId);
		return true;
	}

	SetHintBits(tuple, buffer, HEAP_XMAX_COMMITTED,
				HeapTupleHeaderGetRawXmax(tuple));
	return false;				/* updated by other */
}

/*
 * HeapTupleSatisfiesMVCC
 *		True iff heap tuple is valid for the given MVCC snapshot.
 *
 * See SNAPSHOT_MVCC's definition for the intended behaviour.
 *
 * Notice that here, we will not update the tuple status hint bits if the
 * inserting/deleting transaction is still running according to our snapshot,
 * even if in reality it's committed or aborted by now.  This is intentional.
 * Checking the true transaction state would require access to high-traffic
 * shared data structures, creating contention we'd rather do without, and it
 * would not change the result of our visibility check anyway.  The hint bits
 * will be updated by the first visitor that has a snapshot new enough to see
 * the inserting/deleting transaction as done.  In the meantime, the cost of
 * leaving the hint bits unset is basically that each HeapTupleSatisfiesMVCC
 * call will need to run TransactionIdIsCurrentTransactionId in addition to
 * XidInMVCCSnapshot (but it would have to do the latter anyway).  In the old
 * coding where we tried to set the hint bits as soon as possible, we instead
 * did TransactionIdIsInProgress in each call --- to no avail, as long as the
 * inserting/deleting transaction was still running --- which was more cycles
 * and more contention on the PGXACT array.
 */
static bool
HeapTupleSatisfiesMVCC(HeapTuple htup, Snapshot snapshot,
					   Buffer buffer)
{
	HeapTupleHeader tuple = htup->t_data;

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

	if (!HeapTupleHeaderXminCommitted(tuple))
	{
		if (HeapTupleHeaderXminInvalid(tuple))
			return false;

		/* Used by pre-9.0 binary upgrades */
		if (tuple->t_infomask & HEAP_MOVED_OFF)
		{
			TransactionId xvac = HeapTupleHeaderGetXvac(tuple);

			if (TransactionIdIsCurrentTransactionId(xvac))
				return false;
			if (!XidInMVCCSnapshot(xvac, snapshot))
			{
				if (TransactionIdDidCommit(xvac))
				{
					SetHintBits(tuple, buffer, HEAP_XMIN_INVALID,
								InvalidTransactionId);
					return false;
				}
				SetHintBits(tuple, buffer, HEAP_XMIN_COMMITTED,
							InvalidTransactionId);
			}
		}
		/* Used by pre-9.0 binary upgrades */
		else if (tuple->t_infomask & HEAP_MOVED_IN)
		{
			TransactionId xvac = HeapTupleHeaderGetXvac(tuple);

			if (!TransactionIdIsCurrentTransactionId(xvac))
			{
				if (XidInMVCCSnapshot(xvac, snapshot))
					return false;
				if (TransactionIdDidCommit(xvac))
					SetHintBits(tuple, buffer, HEAP_XMIN_COMMITTED,
								InvalidTransactionId);
				else
				{
					SetHintBits(tuple, buffer, HEAP_XMIN_INVALID,
								InvalidTransactionId);
					return false;
				}
			}
		}
		else if (TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetRawXmin(tuple)))
		{
			if (HeapTupleHeaderGetCmin(tuple) >= snapshot->curcid)
				return false;	/* inserted after scan started */

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

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

			if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
			{
				TransactionId xmax;

				xmax = HeapTupleGetUpdateXid(tuple);

				/* not LOCKED_ONLY, so it has to have an xmax */
				Assert(TransactionIdIsValid(xmax));

				/* updating subtransaction must have aborted */
				if (!TransactionIdIsCurrentTransactionId(xmax))
					return true;
				else if (HeapTupleHeaderGetCmax(tuple) >= snapshot->curcid)
					return true;	/* updated after scan started */
				else
					return false;	/* updated before scan started */
			}

			if (!TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetRawXmax(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 (XidInMVCCSnapshot(HeapTupleHeaderGetRawXmin(tuple), snapshot))
			return false;
		else if (TransactionIdDidCommit(HeapTupleHeaderGetRawXmin(tuple)))
			SetHintBits(tuple, buffer, HEAP_XMIN_COMMITTED,
						HeapTupleHeaderGetRawXmin(tuple));
		else
		{
			/* it must have aborted or crashed */
			SetHintBits(tuple, buffer, HEAP_XMIN_INVALID,
						InvalidTransactionId);
			return false;
		}
	}
	else
	{
		/* xmin is committed, but maybe not according to our snapshot */
		if (!HeapTupleHeaderXminFrozen(tuple) &&
			XidInMVCCSnapshot(HeapTupleHeaderGetRawXmin(tuple), snapshot))
			return false;		/* treat as still in progress */
	}

	/* by here, the inserting transaction has committed */

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

	if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))
		return true;

	if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
	{
		TransactionId xmax;

		/* already checked above */
		Assert(!HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask));

		xmax = HeapTupleGetUpdateXid(tuple);

		/* not LOCKED_ONLY, so it has to have an xmax */
		Assert(TransactionIdIsValid(xmax));

		if (TransactionIdIsCurrentTransactionId(xmax))
		{
			if (HeapTupleHeaderGetCmax(tuple) >= snapshot->curcid)
				return true;	/* deleted after scan started */
			else
				return false;	/* deleted before scan started */
		}
		if (XidInMVCCSnapshot(xmax, snapshot))
			return true;
		if (TransactionIdDidCommit(xmax))
			return false;		/* updating transaction committed */
		/* it must have aborted or crashed */
		return true;
	}

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

		if (XidInMVCCSnapshot(HeapTupleHeaderGetRawXmax(tuple), snapshot))
			return true;

		if (!TransactionIdDidCommit(HeapTupleHeaderGetRawXmax(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,
					HeapTupleHeaderGetRawXmax(tuple));
	}
	else
	{
		/* xmax is committed, but maybe not according to our snapshot */
		if (XidInMVCCSnapshot(HeapTupleHeaderGetRawXmax(tuple), snapshot))
			return true;		/* treat as still in progress */
	}

	/* xmax transaction committed */

	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(HeapTuple htup, TransactionId OldestXmin,
						 Buffer buffer)
{
	HeapTupleHeader tuple = htup->t_data;

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

	/*
	 * 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 (!HeapTupleHeaderXminCommitted(tuple))
	{
		if (HeapTupleHeaderXminInvalid(tuple))
			return HEAPTUPLE_DEAD;
		/* Used by pre-9.0 binary upgrades */
		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);
		}
		/* Used by pre-9.0 binary upgrades */
		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 (TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetRawXmin(tuple)))
		{
			if (tuple->t_infomask & HEAP_XMAX_INVALID)	/* xid invalid */
				return HEAPTUPLE_INSERT_IN_PROGRESS;
			/* only locked? run infomask-only check first, for performance */
			if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask) ||
				HeapTupleHeaderIsOnlyLocked(tuple))
				return HEAPTUPLE_INSERT_IN_PROGRESS;
			/* inserted and then deleted by same xact */
			if (TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetUpdateXid(tuple)))
				return HEAPTUPLE_DELETE_IN_PROGRESS;
			/* deleting subtransaction must have aborted */
			return HEAPTUPLE_INSERT_IN_PROGRESS;
		}
		else if (TransactionIdIsInProgress(HeapTupleHeaderGetRawXmin(tuple)))
		{
			/*
			 * It'd be possible to discern between INSERT/DELETE in progress
			 * here by looking at xmax - but that doesn't seem beneficial for
			 * the majority of callers and even detrimental for some. We'd
			 * rather have callers look at/wait for xmin than xmax. It's
			 * always correct to return INSERT_IN_PROGRESS because that's
			 * what's happening from the view of other backends.
			 */
			return HEAPTUPLE_INSERT_IN_PROGRESS;
		}
		else if (TransactionIdDidCommit(HeapTupleHeaderGetRawXmin(tuple)))
			SetHintBits(tuple, buffer, HEAP_XMIN_COMMITTED,
						HeapTupleHeaderGetRawXmin(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 (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))
	{
		/*
		 * "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.
		 */
		if (!(tuple->t_infomask & HEAP_XMAX_COMMITTED))
		{
			if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
			{
				/*
				 * If it's a pre-pg_upgrade tuple, the multixact cannot
				 * possibly be running; otherwise have to check.
				 */
				if (!HEAP_LOCKED_UPGRADED(tuple->t_infomask) &&
					MultiXactIdIsRunning(HeapTupleHeaderGetRawXmax(tuple),
										 true))
					return HEAPTUPLE_LIVE;
				SetHintBits(tuple, buffer, HEAP_XMAX_INVALID, InvalidTransactionId);
			}
			else
			{
				if (TransactionIdIsInProgress(HeapTupleHeaderGetRawXmax(tuple)))
					return HEAPTUPLE_LIVE;
				SetHintBits(tuple, buffer, HEAP_XMAX_INVALID,
							InvalidTransactionId);
			}
		}

		/*
		 * 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.
		 */

		return HEAPTUPLE_LIVE;
	}

	if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
	{
		TransactionId xmax = HeapTupleGetUpdateXid(tuple);

		/* already checked above */
		Assert(!HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask));

		/* not LOCKED_ONLY, so it has to have an xmax */
		Assert(TransactionIdIsValid(xmax));

		if (TransactionIdIsInProgress(xmax))
			return HEAPTUPLE_DELETE_IN_PROGRESS;
		else if (TransactionIdDidCommit(xmax))
		{
			/*
			 * The multixact might still be running due to lockers.  If the
			 * updater is below the xid horizon, we have to return DEAD
			 * regardless -- otherwise we could end up with a tuple where the
			 * updater has to be removed due to the horizon, but is not pruned
			 * away.  It's not a problem to prune that tuple, because any
			 * remaining lockers will also be present in newer tuple versions.
			 */
			if (!TransactionIdPrecedes(xmax, OldestXmin))
				return HEAPTUPLE_RECENTLY_DEAD;

			return HEAPTUPLE_DEAD;
		}
		else if (!MultiXactIdIsRunning(HeapTupleHeaderGetRawXmax(tuple), false))
		{
			/*
			 * Not in Progress, Not Committed, so either Aborted or crashed.
			 * Mark the Xmax as invalid.
			 */
			SetHintBits(tuple, buffer, HEAP_XMAX_INVALID, InvalidTransactionId);
		}

		return HEAPTUPLE_LIVE;
	}

	if (!(tuple->t_infomask & HEAP_XMAX_COMMITTED))
	{
		if (TransactionIdIsInProgress(HeapTupleHeaderGetRawXmax(tuple)))
			return HEAPTUPLE_DELETE_IN_PROGRESS;
		else if (TransactionIdDidCommit(HeapTupleHeaderGetRawXmax(tuple)))
			SetHintBits(tuple, buffer, HEAP_XMAX_COMMITTED,
						HeapTupleHeaderGetRawXmax(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 perhaps it was recent enough that some open
	 * transactions could still see the tuple.
	 */
	if (!TransactionIdPrecedes(HeapTupleHeaderGetRawXmax(tuple), OldestXmin))
		return HEAPTUPLE_RECENTLY_DEAD;

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


/*
 * HeapTupleSatisfiesNonVacuumable
 *
 *	True if tuple might be visible to some transaction; false if it's
 *	surely dead to everyone, ie, vacuumable.
 *
 *	See SNAPSHOT_TOAST's definition for the intended behaviour.
 *
 *	This is an interface to HeapTupleSatisfiesVacuum that's callable via
 *	HeapTupleSatisfiesSnapshot, so it can be used through a Snapshot.
 *	snapshot->xmin must have been set up with the xmin horizon to use.
 */
static bool
HeapTupleSatisfiesNonVacuumable(HeapTuple htup, Snapshot snapshot,
								Buffer buffer)
{
	return HeapTupleSatisfiesVacuum(htup, snapshot->xmin, buffer)
		!= HEAPTUPLE_DEAD;
}


/*
 * HeapTupleIsSurelyDead
 *
 *	Cheaply determine whether a tuple is surely dead to all onlookers.
 *	We sometimes use this in lieu of HeapTupleSatisfiesVacuum when the
 *	tuple has just been tested by another visibility routine (usually
 *	HeapTupleSatisfiesMVCC) and, therefore, any hint bits that can be set
 *	should already be set.  We assume that if no hint bits are set, the xmin
 *	or xmax transaction is still running.  This is therefore faster than
 *	HeapTupleSatisfiesVacuum, because we don't consult PGXACT nor CLOG.
 *	It's okay to return false when in doubt, but we must return true only
 *	if the tuple is removable.
 */
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);
}

/*
 * Is the tuple really only locked?  That is, is it not updated?
 *
 * It's easy to check just infomask bits if the locker is not a multi; but
 * otherwise we need to verify that the updating transaction has not aborted.
 *
 * This function is here because it follows the same visibility rules laid out
 * at the top of this file.
 */
bool
HeapTupleHeaderIsOnlyLocked(HeapTupleHeader tuple)
{
	TransactionId xmax;

	/* if there's no valid Xmax, then there's obviously no update either */
	if (tuple->t_infomask & HEAP_XMAX_INVALID)
		return true;

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

	/* invalid xmax means no update */
	if (!TransactionIdIsValid(HeapTupleHeaderGetRawXmax(tuple)))
		return true;

	/*
	 * if HEAP_XMAX_LOCK_ONLY is not set and not a multi, then this must
	 * necessarily have been updated
	 */
	if (!(tuple->t_infomask & HEAP_XMAX_IS_MULTI))
		return false;

	/* ... but if it's a multi, then perhaps the updating Xid aborted. */
	xmax = HeapTupleGetUpdateXid(tuple);

	/* not LOCKED_ONLY, so it has to have an xmax */
	Assert(TransactionIdIsValid(xmax));

	if (TransactionIdIsCurrentTransactionId(xmax))
		return false;
	if (TransactionIdIsInProgress(xmax))
		return false;
	if (TransactionIdDidCommit(xmax))
		return false;

	/*
	 * not current, not in progress, not committed -- must have aborted or
	 * crashed
	 */
	return true;
}

/*
 * check whether the transaction id 'xid' is in the pre-sorted array 'xip'.
 */
static bool
TransactionIdInArray(TransactionId xid, TransactionId *xip, Size num)
{
	return bsearch(&xid, xip, num,
				   sizeof(TransactionId), xidComparator) != NULL;
}

/*
 * See the comments for HeapTupleSatisfiesMVCC for the semantics this function
 * obeys.
 *
 * Only usable on tuples from catalog tables!
 *
 * We don't need to support HEAP_MOVED_(IN|OFF) for now because we only support
 * reading catalog pages which couldn't have been created in an older version.
 *
 * We don't set any hint bits in here as it seems unlikely to be beneficial as
 * those should already be set by normal access and it seems to be too
 * dangerous to do so as the semantics of doing so during timetravel are more
 * complicated than when dealing "only" with the present.
 */
static bool
HeapTupleSatisfiesHistoricMVCC(HeapTuple htup, Snapshot snapshot,
							   Buffer buffer)
{
	HeapTupleHeader tuple = htup->t_data;
	TransactionId xmin = HeapTupleHeaderGetXmin(tuple);
	TransactionId xmax = HeapTupleHeaderGetRawXmax(tuple);

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

	/* inserting transaction aborted */
	if (HeapTupleHeaderXminInvalid(tuple))
	{
		Assert(!TransactionIdDidCommit(xmin));
		return false;
	}
	/* check if it's one of our txids, toplevel is also in there */
	else if (TransactionIdInArray(xmin, snapshot->subxip, snapshot->subxcnt))
	{
		bool		resolved;
		CommandId	cmin = HeapTupleHeaderGetRawCommandId(tuple);
		CommandId	cmax = InvalidCommandId;

		/*
		 * another transaction might have (tried to) delete this tuple or
		 * cmin/cmax was stored in a combocid. So we need to lookup the actual
		 * values externally.
		 */
		resolved = ResolveCminCmaxDuringDecoding(HistoricSnapshotGetTupleCids(), snapshot,
												 htup, buffer,
												 &cmin, &cmax);

		if (!resolved)
			elog(ERROR, "could not resolve cmin/cmax of catalog tuple");

		Assert(cmin != InvalidCommandId);

		if (cmin >= snapshot->curcid)
			return false;		/* inserted after scan started */
		/* fall through */
	}
	/* committed before our xmin horizon. Do a normal visibility check. */
	else if (TransactionIdPrecedes(xmin, snapshot->xmin))
	{
		Assert(!(HeapTupleHeaderXminCommitted(tuple) &&
				 !TransactionIdDidCommit(xmin)));

		/* check for hint bit first, consult clog afterwards */
		if (!HeapTupleHeaderXminCommitted(tuple) &&
			!TransactionIdDidCommit(xmin))
			return false;
		/* fall through */
	}
	/* beyond our xmax horizon, i.e. invisible */
	else if (TransactionIdFollowsOrEquals(xmin, snapshot->xmax))
	{
		return false;
	}
	/* check if it's a committed transaction in [xmin, xmax) */
	else if (TransactionIdInArray(xmin, snapshot->xip, snapshot->xcnt))
	{
		/* fall through */
	}

	/*
	 * none of the above, i.e. between [xmin, xmax) but hasn't committed. I.e.
	 * invisible.
	 */
	else
	{
		return false;
	}

	/* at this point we know xmin is visible, go on to check xmax */

	/* xid invalid or aborted */
	if (tuple->t_infomask & HEAP_XMAX_INVALID)
		return true;
	/* locked tuples are always visible */
	else if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))
		return true;

	/*
	 * We can see multis here if we're looking at user tables or if somebody
	 * SELECT ... FOR SHARE/UPDATE a system table.
	 */
	else if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
	{
		xmax = HeapTupleGetUpdateXid(tuple);
	}

	/* check if it's one of our txids, toplevel is also in there */
	if (TransactionIdInArray(xmax, snapshot->subxip, snapshot->subxcnt))
	{
		bool		resolved;
		CommandId	cmin;
		CommandId	cmax = HeapTupleHeaderGetRawCommandId(tuple);

		/* Lookup actual cmin/cmax values */
		resolved = ResolveCminCmaxDuringDecoding(HistoricSnapshotGetTupleCids(), snapshot,
												 htup, buffer,
												 &cmin, &cmax);

		if (!resolved)
			elog(ERROR, "could not resolve combocid to cmax");

		Assert(cmax != InvalidCommandId);

		if (cmax >= snapshot->curcid)
			return true;		/* deleted after scan started */
		else
			return false;		/* deleted before scan started */
	}
	/* below xmin horizon, normal transaction state is valid */
	else if (TransactionIdPrecedes(xmax, snapshot->xmin))
	{
		Assert(!(tuple->t_infomask & HEAP_XMAX_COMMITTED &&
				 !TransactionIdDidCommit(xmax)));

		/* check hint bit first */
		if (tuple->t_infomask & HEAP_XMAX_COMMITTED)
			return false;

		/* check clog */
		return !TransactionIdDidCommit(xmax);
	}
	/* above xmax horizon, we cannot possibly see the deleting transaction */
	else if (TransactionIdFollowsOrEquals(xmax, snapshot->xmax))
		return true;
	/* xmax is between [xmin, xmax), check known committed array */
	else if (TransactionIdInArray(xmax, snapshot->xip, snapshot->xcnt))
		return false;
	/* xmax is between [xmin, xmax), but known not to have committed yet */
	else
		return true;
}

/*
 * HeapTupleSatisfiesVisibility
 *		True iff heap tuple satisfies a time qual.
 *
 * Notes:
 *	Assumes heap tuple is valid, and buffer at least share locked.
 *
 *	Hint bits in the HeapTuple's t_infomask may be updated as a side effect;
 *	if so, the indicated buffer is marked dirty.
 */
bool
HeapTupleSatisfiesVisibility(HeapTuple tup, Snapshot snapshot, Buffer buffer)
{
	switch (snapshot->snapshot_type)
	{
		case SNAPSHOT_MVCC:
			return HeapTupleSatisfiesMVCC(tup, snapshot, buffer);
			break;
		case SNAPSHOT_SELF:
			return HeapTupleSatisfiesSelf(tup, snapshot, buffer);
			break;
		case SNAPSHOT_ANY:
			return HeapTupleSatisfiesAny(tup, snapshot, buffer);
			break;
		case SNAPSHOT_TOAST:
			return HeapTupleSatisfiesToast(tup, snapshot, buffer);
			break;
		case SNAPSHOT_DIRTY:
			return HeapTupleSatisfiesDirty(tup, snapshot, buffer);
			break;
		case SNAPSHOT_HISTORIC_MVCC:
			return HeapTupleSatisfiesHistoricMVCC(tup, snapshot, buffer);
			break;
		case SNAPSHOT_NON_VACUUMABLE:
			return HeapTupleSatisfiesNonVacuumable(tup, snapshot, buffer);
			break;
	}

	return false;				/* keep compiler quiet */
}