Clean up the representation of special snapshots by including a "method

pointer" in every Snapshot struct.  This allows removal of the case-by-case
tests in HeapTupleSatisfiesVisibility, which should make it a bit faster
(I didn't try any performance tests though).  More importantly, we are no
longer violating portable C practices by assuming that small integers are
distinct from all pointer values, and HeapTupleSatisfiesDirty no longer
has a non-reentrant API involving side-effects on a global variable.

There were a couple of places calling HeapTupleSatisfiesXXX routines
directly rather than through the HeapTupleSatisfiesVisibility macro.
Since these places had to be changed anyway, I chose to make them go
through the macro for uniformity.

Along the way I renamed HeapTupleSatisfiesSnapshot to HeapTupleSatisfiesMVCC
to emphasize that it's only used with MVCC-type snapshots.  I was sorely
tempted to rename HeapTupleSatisfiesVisibility to HeapTupleSatisfiesSnapshot,
but forebore for the moment to avoid confusion and reduce the likelihood that
this patch breaks some of the pending patches.  Might want to reconsider
doing that later.

1 files changed, 7 insertions, 5 deletions

diff --git a/src/backend/executor/execMain.c b/src/backend/executor/execMain.c
index 239656dd06b..b2f7159e8c0 100644
--- a/src/backend/executor/execMain.c
+++ b/src/backend/executor/execMain.c
@@ -26,7 +26,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/executor/execMain.c,v 1.290 2007/03/06 02:06:13 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/executor/execMain.c,v 1.291 2007/03/25 19:45:14 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1893,6 +1893,7 @@ EvalPlanQual(EState *estate, Index rti,
 	Relation	relation;
 	HeapTupleData tuple;
 	HeapTuple	copyTuple = NULL;
+	SnapshotData SnapshotDirty;
 	bool		endNode;
 
 	Assert(rti != 0);
@@ -1925,12 +1926,13 @@ EvalPlanQual(EState *estate, Index rti,
 	 *
 	 * Loop here to deal with updated or busy tuples
 	 */
+	InitDirtySnapshot(SnapshotDirty);
 	tuple.t_self = *tid;
 	for (;;)
 	{
 		Buffer		buffer;
 
-		if (heap_fetch(relation, SnapshotDirty, &tuple, &buffer, true, NULL))
+		if (heap_fetch(relation, &SnapshotDirty, &tuple, &buffer, true, NULL))
 		{
 			/*
 			 * If xmin isn't what we're expecting, the slot must have been
@@ -1948,17 +1950,17 @@ EvalPlanQual(EState *estate, Index rti,
 			}
 
 			/* otherwise xmin should not be dirty... */
-			if (TransactionIdIsValid(SnapshotDirty->xmin))
+			if (TransactionIdIsValid(SnapshotDirty.xmin))
 				elog(ERROR, "t_xmin is uncommitted in tuple to be updated");
 
 			/*
 			 * If tuple is being updated by other transaction then we have to
 			 * wait for its commit/abort.
 			 */
-			if (TransactionIdIsValid(SnapshotDirty->xmax))
+			if (TransactionIdIsValid(SnapshotDirty.xmax))
 			{
 				ReleaseBuffer(buffer);
-				XactLockTableWait(SnapshotDirty->xmax);
+				XactLockTableWait(SnapshotDirty.xmax);
 				continue;		/* loop back to repeat heap_fetch */
 			}