Prevent synchronous scan during GIN index build, because GIN is optimized

for inserting tuples in increasing TID order.  It's not clear whether this
fully explains Ivan Sergio Borgonovo's complaint, but simple testing
confirms that a scan that doesn't start at block 0 can slow GIN build by
a factor of three or four.

Backpatch to 8.3.  Sync scan didn't exist before that.

src/backend/access/gin/gininsert.c

@@ -8,7 +8,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *			$PostgreSQL: pgsql/src/backend/access/gin/gininsert.c,v 1.15 2008/09/30 10:52:10 heikki Exp $
+ *			$PostgreSQL: pgsql/src/backend/access/gin/gininsert.c,v 1.16 2008/11/13 17:42:09 tgl Exp $
  *-------------------------------------------------------------------------
  */
 
@@ -340,8 +340,11 @@ ginbuild(PG_FUNCTION_ARGS)
 	buildstate.accum.ginstate = &buildstate.ginstate;
 	ginInitBA(&buildstate.accum);
 
-	/* do the heap scan */
+	/*
-	reltuples = IndexBuildHeapScan(heap, index, indexInfo,
+	 * Do the heap scan.  We disallow sync scan here because dataPlaceToPage
+	 * prefers to receive tuples in TID order.
+	 */
+	reltuples = IndexBuildHeapScan(heap, index, indexInfo, false,
 								   ginBuildCallback, (void *) &buildstate);
 
 	/* dump remaining entries to the index */

src/backend/access/gist/gist.c

@@ -8,7 +8,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/gist/gist.c,v 1.153 2008/11/03 20:47:48 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/gist/gist.c,v 1.154 2008/11/13 17:42:09 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -152,7 +152,7 @@ gistbuild(PG_FUNCTION_ARGS)
 	buildstate.tmpCtx = createTempGistContext();
 
 	/* do the heap scan */
-	reltuples = IndexBuildHeapScan(heap, index, indexInfo,
+	reltuples = IndexBuildHeapScan(heap, index, indexInfo, true,
 								   gistbuildCallback, (void *) &buildstate);
 
 	/* okay, all heap tuples are indexed */

src/backend/access/hash/hash.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/hash/hash.c,v 1.106 2008/10/17 23:50:57 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/hash/hash.c,v 1.107 2008/11/13 17:42:10 tgl Exp $
  *
  * NOTES
  *	  This file contains only the public interface routines.
@@ -93,7 +93,7 @@ hashbuild(PG_FUNCTION_ARGS)
 	buildstate.indtuples = 0;
 
 	/* do the heap scan */
-	reltuples = IndexBuildHeapScan(heap, index, indexInfo,
+	reltuples = IndexBuildHeapScan(heap, index, indexInfo, true,
 								   hashbuildCallback, (void *) &buildstate);
 
 	if (buildstate.spool)

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 1.164 2008/10/31 15:04:59 heikki Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/nbtree/nbtree.c,v 1.165 2008/11/13 17:42:10 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -122,7 +122,7 @@ btbuild(PG_FUNCTION_ARGS)
 		buildstate.spool2 = _bt_spoolinit(index, false, true);
 
 	/* do the heap scan */
-	reltuples = IndexBuildHeapScan(heap, index, indexInfo,
+	reltuples = IndexBuildHeapScan(heap, index, indexInfo, true,
 								   btbuildCallback, (void *) &buildstate);
 
 	/* okay, all heap tuples are indexed */

src/backend/catalog/index.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/catalog/index.c,v 1.307 2008/11/02 01:45:27 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/catalog/index.c,v 1.308 2008/11/13 17:42:10 tgl Exp $
  *
  *
  * INTERFACE ROUTINES
@@ -1513,6 +1513,7 @@ double
 IndexBuildHeapScan(Relation heapRelation,
 				   Relation indexRelation,
 				   IndexInfo *indexInfo,
+				   bool allow_sync,
 				   IndexBuildCallback callback,
 				   void *callback_state)
 {
@@ -1575,7 +1576,12 @@ IndexBuildHeapScan(Relation heapRelation,
 		OldestXmin = GetOldestXmin(heapRelation->rd_rel->relisshared, true);
 	}
 
-	scan = heap_beginscan(heapRelation, snapshot, 0, NULL);
+	scan = heap_beginscan_strat(heapRelation,	/* relation */
+								snapshot,		/* snapshot */
+								0,				/* number of keys */
+								NULL,			/* scan key */
+								true,			/* buffer access strategy OK */
+								allow_sync);	/* syncscan OK? */
 
 	reltuples = 0;
 

src/include/catalog/index.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/catalog/index.h,v 1.75 2008/01/01 19:45:56 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/catalog/index.h,v 1.76 2008/11/13 17:42:10 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -63,6 +63,7 @@ extern void index_build(Relation heapRelation,
 extern double IndexBuildHeapScan(Relation heapRelation,
 				   Relation indexRelation,
 				   IndexInfo *indexInfo,
+				   bool allow_sync,
 				   IndexBuildCallback callback,
 				   void *callback_state);