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, 20 insertions, 27 deletions

diff --git a/src/backend/access/index/indexam.c b/src/backend/access/index/indexam.c
index c4739aa1cd..d59f1529db 100644
--- a/src/backend/access/index/indexam.c
+++ b/src/backend/access/index/indexam.c
@@ -8,20 +8,20 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/index/indexam.c,v 1.104 2008/03/26 21:10:37 alvherre Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/index/indexam.c,v 1.105 2008/04/10 22:25:25 tgl Exp $
  *
  * INTERFACE ROUTINES
  *		index_open		- open an index relation by relation OID
  *		index_close		- close an index relation
  *		index_beginscan - start a scan of an index with amgettuple
- *		index_beginscan_multi - start a scan of an index with amgetmulti
+ *		index_beginscan_bitmap - start a scan of an index with amgetbitmap
  *		index_rescan	- restart a scan of an index
  *		index_endscan	- end a scan
  *		index_insert	- insert an index tuple into a relation
  *		index_markpos	- mark a scan position
  *		index_restrpos	- restore a scan position
  *		index_getnext	- get the next tuple from a scan
- *		index_getmulti	- get multiple tuples from a scan
+ *		index_getbitmap	- get all tuples from a scan
  *		index_bulk_delete	- bulk deletion of index tuples
  *		index_vacuum_cleanup	- post-deletion cleanup of an index
  *		index_getprocid - get a support procedure OID
@@ -227,7 +227,6 @@ index_beginscan(Relation heapRelation,
 	 * Save additional parameters into the scandesc.  Everything else was set
 	 * up by RelationGetIndexScan.
 	 */
-	scan->is_multiscan = false;
 	scan->heapRelation = heapRelation;
 	scan->xs_snapshot = snapshot;
 
@@ -235,15 +234,15 @@ index_beginscan(Relation heapRelation,
 }
 
 /*
- * index_beginscan_multi - start a scan of an index with amgetmulti
+ * index_beginscan_bitmap - start a scan of an index with amgetbitmap
  *
  * As above, caller had better be holding some lock on the parent heap
  * relation, even though it's not explicitly mentioned here.
  */
 IndexScanDesc
-index_beginscan_multi(Relation indexRelation,
-					  Snapshot snapshot,
-					  int nkeys, ScanKey key)
+index_beginscan_bitmap(Relation indexRelation,
+					   Snapshot snapshot,
+					   int nkeys, ScanKey key)
 {
 	IndexScanDesc scan;
 
@@ -253,7 +252,6 @@ index_beginscan_multi(Relation indexRelation,
 	 * Save additional parameters into the scandesc.  Everything else was set
 	 * up by RelationGetIndexScan.
 	 */
-	scan->is_multiscan = true;
 	scan->xs_snapshot = snapshot;
 
 	return scan;
@@ -676,44 +674,39 @@ index_getnext_indexitem(IndexScanDesc scan,
 }
 
 /* ----------------
- *		index_getmulti - get multiple tuples from an index scan
+ *		index_getbitmap - get all tuples at once from an index scan
  *
- * Collects the TIDs of multiple heap tuples satisfying the scan keys.
+ * Adds the TIDs of all heap tuples satisfying the scan keys to a bitmap.
  * Since there's no interlock between the index scan and the eventual heap
  * access, this is only safe to use with MVCC-based snapshots: the heap
  * item slot could have been replaced by a newer tuple by the time we get
  * to it.
  *
- * A TRUE result indicates more calls should occur; a FALSE result says the
- * scan is done.  *returned_tids could be zero or nonzero in either case.
+ * Returns the number of matching tuples found.
  * ----------------
  */
-bool
-index_getmulti(IndexScanDesc scan,
-			   ItemPointer tids, int32 max_tids,
-			   int32 *returned_tids)
+int64
+index_getbitmap(IndexScanDesc scan, TIDBitmap *bitmap)
 {
 	FmgrInfo   *procedure;
-	bool		found;
+	int64		ntids;
 
 	SCAN_CHECKS;
-	GET_SCAN_PROCEDURE(amgetmulti);
+	GET_SCAN_PROCEDURE(amgetbitmap);
 
 	/* just make sure this is false... */
 	scan->kill_prior_tuple = false;
 
 	/*
-	 * have the am's getmulti proc do all the work.
+	 * have the am's getbitmap proc do all the work.
 	 */
-	found = DatumGetBool(FunctionCall4(procedure,
-									   PointerGetDatum(scan),
-									   PointerGetDatum(tids),
-									   Int32GetDatum(max_tids),
-									   PointerGetDatum(returned_tids)));
+	ntids = DatumGetInt64(FunctionCall2(procedure,
+										PointerGetDatum(scan),
+										PointerGetDatum(bitmap)));
 
-	pgstat_count_index_tuples(scan->indexRelation, *returned_tids);
+	pgstat_count_index_tuples(scan->indexRelation, ntids);
 
-	return found;
+	return ntids;
 }
 
 /* ----------------