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.

2 files changed, 10 insertions, 7 deletions

diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index d46308863fe..367831a515a 100644
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.228 2007/02/09 03:35:33 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.229 2007/03/25 19:45:13 tgl Exp $
  *
  *
  * INTERFACE ROUTINES
@@ -1706,7 +1706,7 @@ l1:
 	if (crosscheck != InvalidSnapshot && result == HeapTupleMayBeUpdated)
 	{
 		/* Perform additional check for serializable RI updates */
-		if (!HeapTupleSatisfiesSnapshot(tp.t_data, crosscheck, buffer))
+		if (!HeapTupleSatisfiesVisibility(&tp, crosscheck, buffer))
 			result = HeapTupleUpdated;
 	}
 
@@ -2025,7 +2025,7 @@ l2:
 	if (crosscheck != InvalidSnapshot && result == HeapTupleMayBeUpdated)
 	{
 		/* Perform additional check for serializable RI updates */
-		if (!HeapTupleSatisfiesSnapshot(oldtup.t_data, crosscheck, buffer))
+		if (!HeapTupleSatisfiesVisibility(&oldtup, crosscheck, buffer))
 			result = HeapTupleUpdated;
 	}
 
diff --git a/src/backend/access/nbtree/nbtinsert.c b/src/backend/access/nbtree/nbtinsert.c
index d2992374e97..c1671ce333c 100644
--- a/src/backend/access/nbtree/nbtinsert.c
+++ b/src/backend/access/nbtree/nbtinsert.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/nbtree/nbtinsert.c,v 1.154 2007/03/05 14:13:12 neilc Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/nbtree/nbtinsert.c,v 1.155 2007/03/25 19:45:14 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -176,11 +176,14 @@ _bt_check_unique(Relation rel, IndexTuple itup, Relation heapRel,
 {
 	TupleDesc	itupdesc = RelationGetDescr(rel);
 	int			natts = rel->rd_rel->relnatts;
+	SnapshotData SnapshotDirty;
 	OffsetNumber maxoff;
 	Page		page;
 	BTPageOpaque opaque;
 	Buffer		nbuf = InvalidBuffer;
 
+	InitDirtySnapshot(SnapshotDirty);
+
 	page = BufferGetPage(buf);
 	opaque = (BTPageOpaque) PageGetSpecialPointer(page);
 	maxoff = PageGetMaxOffsetNumber(page);
@@ -232,13 +235,13 @@ _bt_check_unique(Relation rel, IndexTuple itup, Relation heapRel,
 				/* okay, we gotta fetch the heap tuple ... */
 				curitup = (IndexTuple) PageGetItem(page, curitemid);
 				htup.t_self = curitup->t_tid;
-				if (heap_fetch(heapRel, SnapshotDirty, &htup, &hbuffer,
+				if (heap_fetch(heapRel, &SnapshotDirty, &htup, &hbuffer,
 							   true, NULL))
 				{
 					/* it is a duplicate */
 					TransactionId xwait =
-					(TransactionIdIsValid(SnapshotDirty->xmin)) ?
-					SnapshotDirty->xmin : SnapshotDirty->xmax;
+					(TransactionIdIsValid(SnapshotDirty.xmin)) ?
+					SnapshotDirty.xmin : SnapshotDirty.xmax;
 
 					ReleaseBuffer(hbuffer);