Replace "amgetmulti" AM functions with "amgetbitmap", in which the whole

indexscan always occurs in one call, and the results are returned in a
TIDBitmap instead of a limited-size array of TIDs.  This should improve
speed a little by reducing AM entry/exit overhead, and it is necessary
infrastructure if we are ever to support bitmap indexes.

In an only slightly related change, add support for TIDBitmaps to preserve
(somewhat lossily) the knowledge that particular TIDs reported by an index
need to have their quals rechecked when the heap is visited.  This facility
is not really used yet; we'll need to extend the forced-recheck feature to
plain indexscans before it's useful, and that hasn't been coded yet.
The intent is to use it to clean up 8.3's horrid @@@ kluge for text search
with weighted queries.  There might be other uses in future, but that one
alone is sufficient reason.

Heikki Linnakangas, with some adjustments by me.

1 files changed, 22 insertions, 33 deletions

diff --git a/src/backend/access/nbtree/nbtree.c b/src/backend/access/nbtree/nbtree.c
index 5cfa8f315d7..d96348ace46 100644
--- a/src/backend/access/nbtree/nbtree.c
+++ b/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 1.156 2008/01/01 19:45:46 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/nbtree/nbtree.c,v 1.157 2008/04/10 22:25:25 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -22,6 +22,7 @@
 #include "access/nbtree.h"
 #include "catalog/index.h"
 #include "commands/vacuum.h"
+#include "miscadmin.h"
 #include "storage/freespace.h"
 #include "storage/lmgr.h"
 #include "utils/memutils.h"
@@ -278,42 +279,29 @@ btgettuple(PG_FUNCTION_ARGS)
 }
 
 /*
- * btgetmulti() -- get multiple tuples at once
- *
- * In the current implementation there seems no strong reason to stop at
- * index page boundaries; we just press on until we fill the caller's buffer
- * or run out of matches.
+ * btgetbitmap() -- gets all matching tuples, and adds them to a bitmap
  */
 Datum
-btgetmulti(PG_FUNCTION_ARGS)
+btgetbitmap(PG_FUNCTION_ARGS)
 {
 	IndexScanDesc scan = (IndexScanDesc) PG_GETARG_POINTER(0);
-	ItemPointer tids = (ItemPointer) PG_GETARG_POINTER(1);
-	int32		max_tids = PG_GETARG_INT32(2);
-	int32	   *returned_tids = (int32 *) PG_GETARG_POINTER(3);
+	TIDBitmap *tbm = (TIDBitmap *) PG_GETARG_POINTER(1);
 	BTScanOpaque so = (BTScanOpaque) scan->opaque;
-	bool		res = true;
-	int32		ntids = 0;
-
-	if (max_tids <= 0)			/* behave correctly in boundary case */
-		PG_RETURN_BOOL(true);
+	int64		ntids = 0;
+	ItemPointer heapTid;
 
-	/* If we haven't started the scan yet, fetch the first page & tuple. */
-	if (!BTScanPosIsValid(so->currPos))
+	/* Fetch the first page & tuple. */
+	if (!_bt_first(scan, ForwardScanDirection))
 	{
-		res = _bt_first(scan, ForwardScanDirection);
-		if (!res)
-		{
-			/* empty scan */
-			*returned_tids = ntids;
-			PG_RETURN_BOOL(res);
-		}
-		/* Save tuple ID, and continue scanning */
-		tids[ntids] = scan->xs_ctup.t_self;
-		ntids++;
+		/* empty scan */
+		PG_RETURN_INT64(0);
 	}
+	/* Save tuple ID, and continue scanning */
+	heapTid = &scan->xs_ctup.t_self;
+	tbm_add_tuples(tbm, heapTid, 1, false);
+	ntids++;
 
-	while (ntids < max_tids)
+	for (;;)
 	{
 		/*
 		 * Advance to next tuple within page.  This is the same as the easy
@@ -321,19 +309,20 @@ btgetmulti(PG_FUNCTION_ARGS)
 		 */
 		if (++so->currPos.itemIndex > so->currPos.lastItem)
 		{
+			CHECK_FOR_INTERRUPTS();
+
 			/* let _bt_next do the heavy lifting */
-			res = _bt_next(scan, ForwardScanDirection);
-			if (!res)
+			if (!_bt_next(scan, ForwardScanDirection))
 				break;
 		}
 
 		/* Save tuple ID, and continue scanning */
-		tids[ntids] = so->currPos.items[so->currPos.itemIndex].heapTid;
+		heapTid = &so->currPos.items[so->currPos.itemIndex].heapTid;
+		tbm_add_tuples(tbm, heapTid, 1, false);
 		ntids++;
 	}
 
-	*returned_tids = ntids;
-	PG_RETURN_BOOL(res);
+	PG_RETURN_INT64(ntids);
 }
 
 /*