HOT updates. When we update a tuple without changing any of its indexed

columns, and the new version can be stored on the same heap page, we no longer
generate extra index entries for the new version.  Instead, index searches
follow the HOT-chain links to ensure they find the correct tuple version.

In addition, this patch introduces the ability to "prune" dead tuples on a
per-page basis, without having to do a complete VACUUM pass to recover space.
VACUUM is still needed to clean up dead index entries, however.

Pavan Deolasee, with help from a bunch of other people.

src/backend/optimizer/util/plancat.c

@@ -9,7 +9,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/util/plancat.c,v 1.136 2007/05/31 16:57:34 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/util/plancat.c,v 1.137 2007/09/20 17:56:31 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -19,6 +19,7 @@
 
 #include "access/genam.h"
 #include "access/heapam.h"
+#include "access/transam.h"
 #include "catalog/pg_inherits.h"
 #include "nodes/makefuncs.h"
 #include "optimizer/clauses.h"
@@ -164,6 +165,20 @@ get_relation_info(PlannerInfo *root, Oid relationObjectId, bool inhparent,
 				continue;
 			}
 
+			/*
+			 * If the index is valid, but cannot yet be used, ignore it;
+			 * but mark the plan we are generating as transient.
+			 * See src/backend/access/heap/README.HOT for discussion.
+			 */
+			if (index->indcheckxmin &&
+				!TransactionIdPrecedes(HeapTupleHeaderGetXmin(indexRelation->rd_indextuple->t_data),
+									   TransactionXmin))
+			{
+				root->glob->transientPlan = true;
+				index_close(indexRelation, NoLock);
+				continue;
+			}
+
 			info = makeNode(IndexOptInfo);
 
 			info->indexoid = index->indexrelid;