Implement "fastupdate" support for GIN indexes, in which we try to accumulate

multiple index entries in a holding area before adding them to the main index
structure.  This helps because bulk insert is (usually) significantly faster
than retail insert for GIN.

This patch also removes GIN support for amgettuple-style index scans.  The
API defined for amgettuple is difficult to support with fastupdate, and
the previously committed partial-match feature didn't really work with
it either.  We might eventually figure a way to put back amgettuple
support, but it won't happen for 8.4.

catversion bumped because of change in GIN's pg_am entry, and because
the format of GIN indexes changed on-disk (there's a metapage now,
and possibly a pending list).

Teodor Sigaev

src/include/access/genam.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/access/genam.h,v 1.75 2009/01/01 17:23:55 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/access/genam.h,v 1.76 2009/03/24 20:17:14 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -41,6 +41,7 @@ typedef struct IndexVacuumInfo
 {
 	Relation	index;			/* the index being vacuumed */
 	bool		vacuum_full;	/* VACUUM FULL (we have exclusive lock) */
+	bool		analyze_only;	/* ANALYZE (without any actual vacuum) */
 	int			message_level;	/* ereport level for progress messages */
 	double		num_heap_tuples;	/* tuples remaining in heap */
 	BufferAccessStrategy strategy;		/* access strategy for reads */