Improve the IndexVacuumInfo/IndexBulkDeleteResult API to allow somewhat sane

behavior in cases where we don't know the heap tuple count accurately; in
particular partial vacuum, but this also makes the API a bit more useful
for ANALYZE.  This patch adds "estimated_count" flags to both structs so
that an approximate count can be flagged as such, and adjusts the logic
so that approximate counts are not used for updating pg_class.reltuples.

This fixes my previous complaint that VACUUM was putting ridiculous values
into pg_class.reltuples for indexes.  The actual impact of that bug is
limited, because the planner only pays attention to reltuples for an index
if the index is partial; which probably explains why beta testers hadn't
noticed a degradation in plan quality from it.  But it needs to be fixed.

The whole thing is a bit messy and should be redesigned in future, because
reltuples now has the potential to drift quite far away from reality when
a long period elapses with no non-partial vacuums.  But this is as good as
it's going to get for 8.4.

1 files changed, 3 insertions, 2 deletions

diff --git a/src/backend/access/gist/gistvacuum.c b/src/backend/access/gist/gistvacuum.c
index 01b8512d070..833e6c574eb 100644
--- a/src/backend/access/gist/gistvacuum.c
+++ b/src/backend/access/gist/gistvacuum.c
@@ -8,7 +8,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/gist/gistvacuum.c,v 1.43 2009/03/24 20:17:11 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/gist/gistvacuum.c,v 1.44 2009/06/06 22:13:50 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -524,8 +524,8 @@ gistvacuumcleanup(PG_FUNCTION_ARGS)
 	{
 		stats = (GistBulkDeleteResult *) palloc0(sizeof(GistBulkDeleteResult));
 		/* use heap's tuple count */
-		Assert(info->num_heap_tuples >= 0);
 		stats->std.num_index_tuples = info->num_heap_tuples;
+		stats->std.estimated_count = info->estimated_count;
 
 		/*
 		 * XXX the above is wrong if index is partial.	Would it be OK to just
@@ -679,6 +679,7 @@ gistbulkdelete(PG_FUNCTION_ARGS)
 	if (stats == NULL)
 		stats = (GistBulkDeleteResult *) palloc0(sizeof(GistBulkDeleteResult));
 	/* we'll re-count the tuples each time */
+	stats->std.estimated_count = false;
 	stats->std.num_index_tuples = 0;
 
 	stack = (GistBDItem *) palloc0(sizeof(GistBDItem));