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From: Melanie Plageman <[email protected]>
Subject: [PATCH v19 01/21] BitmapHeapScan: begin scan after bitmap creation
Date: Mon, 12 Feb 2024 18:50:29 -0500

It makes more sense for BitmapHeapScan to scan the index, build the
bitmap, and only then begin the scan on the underlying table.

This is mostly a cosmetic change for now, but later commits will need
to pass parameters to table_beginscan_bm() that are unavailable in
ExecInitBitmapHeapScan().

Author: Melanie Plageman
Reviewed-by: Tomas Vondra, Andres Freund, Heikki Linnakangas
Discussion: https://postgr.es/m/CAAKRu_ZwCwWFeL_H3ia26bP2e7HiKLWt0ZmGXPVwPO6uXq0vaA%40mail.gmail.com
---
 src/backend/executor/nodeBitmapHeapscan.c | 27 +++++++++++++++++------
 1 file changed, 20 insertions(+), 7 deletions(-)

diff --git a/src/backend/executor/nodeBitmapHeapscan.c b/src/backend/executor/nodeBitmapHeapscan.c
index cee7f45aabe..c8c466e3c5c 100644
--- a/src/backend/executor/nodeBitmapHeapscan.c
+++ b/src/backend/executor/nodeBitmapHeapscan.c
@@ -178,6 +178,21 @@ BitmapHeapNext(BitmapHeapScanState *node)
 			}
 #endif							/* USE_PREFETCH */
 		}
+
+		/*
+		 * If this is the first scan of the underlying table, create the table
+		 * scan descriptor and begin the scan.
+		 */
+		if (!scan)
+		{
+			scan = table_beginscan_bm(node->ss.ss_currentRelation,
+									  node->ss.ps.state->es_snapshot,
+									  0,
+									  NULL);
+
+			node->ss.ss_currentScanDesc = scan;
+		}
+
 		node->initialized = true;
 	}
 
@@ -601,7 +616,8 @@ ExecReScanBitmapHeapScan(BitmapHeapScanState *node)
 	PlanState  *outerPlan = outerPlanState(node);
 
 	/* rescan to release any page pin */
-	table_rescan(node->ss.ss_currentScanDesc, NULL);
+	if (node->ss.ss_currentScanDesc)
+		table_rescan(node->ss.ss_currentScanDesc, NULL);
 
 	/* release bitmaps and buffers if any */
 	if (node->tbmiterator)
@@ -678,7 +694,9 @@ ExecEndBitmapHeapScan(BitmapHeapScanState *node)
 	/*
 	 * close heap scan
 	 */
-	table_endscan(scanDesc);
+	if (scanDesc)
+		table_endscan(scanDesc);
+
 }
 
 /* ----------------------------------------------------------------
@@ -783,11 +801,6 @@ ExecInitBitmapHeapScan(BitmapHeapScan *node, EState *estate, int eflags)
 
 	scanstate->ss.ss_currentRelation = currentRelation;
 
-	scanstate->ss.ss_currentScanDesc = table_beginscan_bm(currentRelation,
-														  estate->es_snapshot,
-														  0,
-														  NULL);
-
 	/*
 	 * all done.
 	 */
-- 
2.40.1


--clv5reqgj4vdihqz
Content-Type: text/x-diff; charset=us-ascii
Content-Disposition: attachment;
	filename="v19-0002-BitmapHeapScan-postpone-setting-can_skip_fetch.patch"

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