Adjust nodeBitmapIndexscan to keep the target index opened from plan

startup to end, rather than re-opening it in each MultiExecBitmapIndexScan
call.  I had foolishly thought that opening/closing wouldn't be much
more expensive than a rescan call, but that was sheer brain fade.

This seems to fix about half of the performance lossage reported by
Sergey Koposov.  I'm still not sure where the other half went.

src/backend/executor/nodeBitmapIndexscan.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/executor/nodeBitmapIndexscan.c,v 1.7 2005/04/25 01:30:12 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/executor/nodeBitmapIndexscan.c,v 1.8 2005/05/05 03:37:23 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -38,8 +38,6 @@ MultiExecBitmapIndexScan(BitmapIndexScanState *node)
 {
 #define MAX_TIDS	1024
 	TIDBitmap  *tbm;
-	Oid			indexid;
-	Relation	indexRelation;
 	IndexScanDesc scandesc;
 	ItemPointerData tids[MAX_TIDS];
 	int32		ntids;
@@ -49,6 +47,11 @@ MultiExecBitmapIndexScan(BitmapIndexScanState *node)
 	if (node->ss.ps.instrument)
 		InstrStartNode(node->ss.ps.instrument);
 
+	/*
+	 * extract necessary information from index scan node
+	 */
+	scandesc = node->biss_ScanDesc;
+
 	/*
 	 * If we have runtime keys and they've not already been set up, do it
 	 * now.
@@ -56,24 +59,6 @@ MultiExecBitmapIndexScan(BitmapIndexScanState *node)
 	if (node->biss_RuntimeKeyInfo && !node->biss_RuntimeKeysReady)
 		ExecReScan((PlanState *) node, NULL);
 
-	/*
-	 * We do not open or lock the base relation here.  We assume that an
-	 * ancestor BitmapHeapScan node is holding AccessShareLock on the
-	 * heap relation throughout the execution of the plan tree.
-	 */
-
-	/*
-	 * open the index relation and initialize relation and scan
-	 * descriptors.  Note we acquire no locks here; the index machinery
-	 * does its own locks and unlocks.
-	 */
-	indexid = ((BitmapIndexScan *) node->ss.ps.plan)->indexid;
-	indexRelation = index_open(indexid);
-	scandesc = index_beginscan_multi(indexRelation,
-									 node->ss.ps.state->es_snapshot,
-									 node->biss_NumScanKeys,
-									 node->biss_ScanKeys);
-
 	/*
 	 * Prepare the result bitmap.  Normally we just create a new one to pass
 	 * back; however, our parent node is allowed to store a pre-made one
@@ -110,12 +95,6 @@ MultiExecBitmapIndexScan(BitmapIndexScanState *node)
 		CHECK_FOR_INTERRUPTS();
 	}
 
-	/*
-	 * close the index relation
-	 */
-	index_endscan(scandesc);
-	index_close(indexRelation);
-
 	/* must provide our own instrumentation support */
 	if (node->ss.ps.instrument)
 		InstrStopNodeMulti(node->ss.ps.instrument, nTuples);
@@ -127,7 +106,7 @@ MultiExecBitmapIndexScan(BitmapIndexScanState *node)
  *		ExecBitmapIndexReScan(node)
  *
  *		Recalculates the value of the scan keys whose value depends on
- *		information known at runtime.
+ *		information known at runtime and rescans the indexed relation.
  * ----------------------------------------------------------------
  */
 void
@@ -169,6 +148,9 @@ ExecBitmapIndexReScan(BitmapIndexScanState *node, ExprContext *exprCtxt)
 								 node->biss_NumScanKeys);
 		node->biss_RuntimeKeysReady = true;
 	}
+
+	/* reset index scan */
+	index_rescan(node->biss_ScanDesc, node->biss_ScanKeys);
 }
 
 /* ----------------------------------------------------------------
@@ -178,6 +160,15 @@ ExecBitmapIndexReScan(BitmapIndexScanState *node, ExprContext *exprCtxt)
 void
 ExecEndBitmapIndexScan(BitmapIndexScanState *node)
 {
+	Relation	indexRelationDesc;
+	IndexScanDesc indexScanDesc;
+
+	/*
+	 * extract information from the node
+	 */
+	indexRelationDesc = node->biss_RelationDesc;
+	indexScanDesc = node->biss_ScanDesc;
+
 	/*
 	 * Free the exprcontext ... now dead code, see ExecFreeExprContext
 	 */
@@ -185,6 +176,12 @@ ExecEndBitmapIndexScan(BitmapIndexScanState *node)
 	if (node->biss_RuntimeContext)
 		FreeExprContext(node->biss_RuntimeContext);
 #endif
+
+	/*
+	 * close the index relation
+	 */
+	index_endscan(indexScanDesc);
+	index_close(indexRelationDesc);
 }
 
 /* ----------------------------------------------------------------
@@ -272,10 +269,27 @@ ExecInitBitmapIndexScan(BitmapIndexScan *node, EState *estate)
 		indexstate->biss_RuntimeContext = NULL;
 	}
 
-	/* We don't keep the table or index open across calls */
+	/*
+	 * We do not open or lock the base relation here.  We assume that an
+	 * ancestor BitmapHeapScan node is holding AccessShareLock on the
+	 * heap relation throughout the execution of the plan tree.
+	 */
+
 	indexstate->ss.ss_currentRelation = NULL;
 	indexstate->ss.ss_currentScanDesc = NULL;
 
+	/*
+	 * open the index relation and initialize relation and scan
+	 * descriptors.  Note we acquire no locks here; the index machinery
+	 * does its own locks and unlocks.
+	 */
+	indexstate->biss_RelationDesc = index_open(node->indexid);
+	indexstate->biss_ScanDesc =
+		index_beginscan_multi(indexstate->biss_RelationDesc,
+							  estate->es_snapshot,
+							  numScanKeys,
+							  scanKeys);
+
 	/*
 	 * all done.
 	 */

src/include/nodes/execnodes.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/nodes/execnodes.h,v 1.130 2005/04/28 21:47:17 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/nodes/execnodes.h,v 1.131 2005/05/05 03:37:23 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -897,6 +897,8 @@ typedef struct IndexScanState
  *						   that will be evaluated at runtime
  *		RuntimeContext	   expr context for evaling runtime Skeys
  *		RuntimeKeysReady   true if runtime Skeys have been computed
+ *		RelationDesc	   index relation descriptor
+ *		ScanDesc		   index scan descriptor
  * ----------------
  */
 typedef struct BitmapIndexScanState
@@ -908,6 +910,8 @@ typedef struct BitmapIndexScanState
 	ExprState **biss_RuntimeKeyInfo;
 	ExprContext *biss_RuntimeContext;
 	bool		biss_RuntimeKeysReady;
+	Relation	biss_RelationDesc;
+	IndexScanDesc biss_ScanDesc;
 } BitmapIndexScanState;
 
 /* ----------------