Index FSMs needs to be vacuumed as well. Report by Jeff Davis.

src/backend/access/gin/ginvacuum.c

@@ -8,7 +8,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *			$PostgreSQL: pgsql/src/backend/access/gin/ginvacuum.c,v 1.22 2008/09/30 10:52:10 heikki Exp $
+ *			$PostgreSQL: pgsql/src/backend/access/gin/ginvacuum.c,v 1.23 2008/10/06 08:04:11 heikki Exp $
  *-------------------------------------------------------------------------
  */
 
@@ -744,6 +744,9 @@ ginvacuumcleanup(PG_FUNCTION_ARGS)
 		totFreePages = totFreePages - stats->pages_removed;
 	}
 
+	/* Finally, vacuum the FSM */
+	IndexFreeSpaceMapVacuum(info->index);
+
 	stats->pages_free = totFreePages;
 
 	if (needLock)

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 1.37 2008/09/30 10:52:10 heikki Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/gist/gistvacuum.c,v 1.38 2008/10/06 08:04:11 heikki Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -619,6 +619,9 @@ gistvacuumcleanup(PG_FUNCTION_ARGS)
 		totFreePages = totFreePages - stats->std.pages_removed;
 	}
 
+	/* Finally, vacuum the FSM */
+	IndexFreeSpaceMapVacuum(info->index);
+
 	/* return statistics */
 	stats->std.pages_free = totFreePages;
 	if (needLock)

src/backend/access/nbtree/nbtree.c

@@ -12,7 +12,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/nbtree/nbtree.c,v 1.162 2008/09/30 10:52:10 heikki Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/nbtree/nbtree.c,v 1.163 2008/10/06 08:04:11 heikki Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -574,6 +574,9 @@ btvacuumcleanup(PG_FUNCTION_ARGS)
 		btvacuumscan(info, stats, NULL, NULL, 0);
 	}
 
+	/* Finally, vacuum the FSM */
+	IndexFreeSpaceMapVacuum(info->index);
+
 	/*
 	 * During a non-FULL vacuum it's quite possible for us to be fooled by
 	 * concurrent page splits into double-counting some index tuples, so

src/backend/storage/freespace/indexfsm.c

@@ -8,7 +8,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/freespace/indexfsm.c,v 1.1 2008/09/30 10:52:13 heikki Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/freespace/indexfsm.c,v 1.2 2008/10/06 08:04:11 heikki Exp $
  *
  *
  * NOTES:
@@ -90,3 +90,12 @@ IndexFreeSpaceMapTruncate(Relation rel, BlockNumber nblocks)
 {
 	FreeSpaceMapTruncateRel(rel, nblocks);
 }
+
+/*
+ * IndexFreeSpaceMapVacuum - scan and fix any inconsistencies in the FSM
+ */
+void
+IndexFreeSpaceMapVacuum(Relation rel)
+{
+	FreeSpaceMapVacuum(rel);
+}

src/include/storage/indexfsm.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/storage/indexfsm.h,v 1.1 2008/09/30 10:52:14 heikki Exp $
+ * $PostgreSQL: pgsql/src/include/storage/indexfsm.h,v 1.2 2008/10/06 08:04:11 heikki Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -16,12 +16,12 @@
 
 #include "utils/rel.h"
 
-extern void InitIndexFreeSpaceMap(Relation rel);
-
 extern BlockNumber GetFreeIndexPage(Relation rel);
 extern void RecordFreeIndexPage(Relation rel, BlockNumber page);
 extern void RecordUsedIndexPage(Relation rel, BlockNumber page);
 
+extern void InitIndexFreeSpaceMap(Relation rel);
 extern void IndexFreeSpaceMapTruncate(Relation rel, BlockNumber nblocks);
+extern void IndexFreeSpaceMapVacuum(Relation rel);
 
 #endif   /* INDEXFSM_H */