v45-0003-Pass-down-information-on-table-modification-to-s.patch

From 7b400e9ccd7d8d83358bd503b7209c8ed1ec7ea3 Mon Sep 17 00:00:00 2001
From: Melanie Plageman <melanieplageman@gmail.com>
Date: Mon, 2 Mar 2026 16:31:33 -0500
Subject: [PATCH v45 3/5] Pass down information on table modification to scan
 node

Pass down information to sequential scan, index [only] scan, bitmap
table scan, sample scan, and TID range scan nodes on whether or not the
query modifies the relation being scanned. A later commit will use this
information to update the VM during on-access pruning only if the
relation is not modified by the query.

Author: Melanie Plageman <melanieplageman@gmail.com>
Reviewed-by: Andres Freund <andres@anarazel.de>
Reviewed-by: Andrey Borodin <x4mmm@yandex-team.ru>
Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Discussion: https://postgr.es/m/4379FDA3-9446-4E2C-9C15-32EFE8D4F31B%40yandex-team.ru
---
 src/backend/executor/execUtils.c          |  8 ++++++++
 src/backend/executor/nodeBitmapHeapscan.c |  5 ++++-
 src/backend/executor/nodeIndexonlyscan.c  | 11 ++++++++---
 src/backend/executor/nodeIndexscan.c      | 16 ++++++++++++----
 src/backend/executor/nodeSamplescan.c     |  5 ++++-
 src/backend/executor/nodeSeqscan.c        | 14 +++++++++++---
 src/backend/executor/nodeTidrangescan.c   | 15 ++++++++++++---
 src/include/access/tableam.h              |  3 +++
 src/include/executor/executor.h           |  2 ++
 9 files changed, 64 insertions(+), 15 deletions(-)

diff --git a/src/backend/executor/execUtils.c b/src/backend/executor/execUtils.c
index 9886ab06b69..d2ffe28e010 100644
--- a/src/backend/executor/execUtils.c
+++ b/src/backend/executor/execUtils.c
@@ -736,6 +736,14 @@ ExecRelationIsTargetRelation(EState *estate, Index scanrelid)
 	return list_member_int(estate->es_plannedstmt->resultRelations, scanrelid);
 }
 
+/* Return true if the scan node's relation is not modified by the query */
+bool
+ScanRelIsReadOnly(ScanState *ss)
+{
+	return !bms_is_member(((Scan *) ss->ps.plan)->scanrelid,
+						  ss->ps.state->es_plannedstmt->modifiedRelids);
+}
+
 /* ----------------------------------------------------------------
  *		ExecOpenScanRelation
  *
diff --git a/src/backend/executor/nodeBitmapHeapscan.c b/src/backend/executor/nodeBitmapHeapscan.c
index 7e2c1b7467b..dba6c31d188 100644
--- a/src/backend/executor/nodeBitmapHeapscan.c
+++ b/src/backend/executor/nodeBitmapHeapscan.c
@@ -144,9 +144,12 @@ BitmapTableScanSetup(BitmapHeapScanState *node)
 	 */
 	if (!node->ss.ss_currentScanDesc)
 	{
+		uint32		flags = ScanRelIsReadOnly(&node->ss) ?
+			SO_HINT_REL_READ_ONLY : 0;
+
 		node->ss.ss_currentScanDesc =
 			table_beginscan_bm(node->ss.ss_currentRelation,
-							   0,
+							   flags,
 							   node->ss.ps.state->es_snapshot,
 							   0,
 							   NULL);
diff --git a/src/backend/executor/nodeIndexonlyscan.c b/src/backend/executor/nodeIndexonlyscan.c
index 5cacb4b215a..88491249a9a 100644
--- a/src/backend/executor/nodeIndexonlyscan.c
+++ b/src/backend/executor/nodeIndexonlyscan.c
@@ -85,6 +85,9 @@ IndexOnlyNext(IndexOnlyScanState *node)
 
 	if (scandesc == NULL)
 	{
+		uint32		flags = ScanRelIsReadOnly(&node->ss) ?
+			SO_HINT_REL_READ_ONLY : 0;
+
 		/*
 		 * We reach here if the index only scan is not parallel, or if we're
 		 * serially executing an index only scan that was planned to be
@@ -92,7 +95,7 @@ IndexOnlyNext(IndexOnlyScanState *node)
 		 */
 		scandesc = index_beginscan(node->ss.ss_currentRelation,
 								   node->ioss_RelationDesc,
-								   0,	/* flags */
+								   flags,
 								   estate->es_snapshot,
 								   node->ioss_Instrument,
 								   node->ioss_NumScanKeys,
@@ -792,7 +795,8 @@ ExecIndexOnlyScanInitializeDSM(IndexOnlyScanState *node,
 	node->ioss_ScanDesc =
 		index_beginscan_parallel(node->ss.ss_currentRelation,
 								 node->ioss_RelationDesc,
-								 0, /* flags */
+								 ScanRelIsReadOnly(&node->ss) ?
+								 SO_HINT_REL_READ_ONLY : 0,
 								 node->ioss_Instrument,
 								 node->ioss_NumScanKeys,
 								 node->ioss_NumOrderByKeys,
@@ -859,7 +863,8 @@ ExecIndexOnlyScanInitializeWorker(IndexOnlyScanState *node,
 	node->ioss_ScanDesc =
 		index_beginscan_parallel(node->ss.ss_currentRelation,
 								 node->ioss_RelationDesc,
-								 0, /* flags */
+								 ScanRelIsReadOnly(&node->ss) ?
+								 SO_HINT_REL_READ_ONLY : 0,
 								 node->ioss_Instrument,
 								 node->ioss_NumScanKeys,
 								 node->ioss_NumOrderByKeys,
diff --git a/src/backend/executor/nodeIndexscan.c b/src/backend/executor/nodeIndexscan.c
index aaef31dbbad..16ec455a964 100644
--- a/src/backend/executor/nodeIndexscan.c
+++ b/src/backend/executor/nodeIndexscan.c
@@ -104,13 +104,16 @@ IndexNext(IndexScanState *node)
 
 	if (scandesc == NULL)
 	{
+		uint32		flags = ScanRelIsReadOnly(&node->ss) ?
+			SO_HINT_REL_READ_ONLY : 0;
+
 		/*
 		 * We reach here if the index scan is not parallel, or if we're
 		 * serially executing an index scan that was planned to be parallel.
 		 */
 		scandesc = index_beginscan(node->ss.ss_currentRelation,
 								   node->iss_RelationDesc,
-								   0,	/* flags */
+								   flags,
 								   estate->es_snapshot,
 								   node->iss_Instrument,
 								   node->iss_NumScanKeys,
@@ -201,13 +204,16 @@ IndexNextWithReorder(IndexScanState *node)
 
 	if (scandesc == NULL)
 	{
+		uint32		flags = ScanRelIsReadOnly(&node->ss) ?
+			SO_HINT_REL_READ_ONLY : 0;
+
 		/*
 		 * We reach here if the index scan is not parallel, or if we're
 		 * serially executing an index scan that was planned to be parallel.
 		 */
 		scandesc = index_beginscan(node->ss.ss_currentRelation,
 								   node->iss_RelationDesc,
-								   0,	/* flags */
+								   flags,
 								   estate->es_snapshot,
 								   node->iss_Instrument,
 								   node->iss_NumScanKeys,
@@ -1729,7 +1735,8 @@ ExecIndexScanInitializeDSM(IndexScanState *node,
 	node->iss_ScanDesc =
 		index_beginscan_parallel(node->ss.ss_currentRelation,
 								 node->iss_RelationDesc,
-								 0, /* flags */
+								 ScanRelIsReadOnly(&node->ss) ?
+								 SO_HINT_REL_READ_ONLY : 0,
 								 node->iss_Instrument,
 								 node->iss_NumScanKeys,
 								 node->iss_NumOrderByKeys,
@@ -1794,7 +1801,8 @@ ExecIndexScanInitializeWorker(IndexScanState *node,
 	node->iss_ScanDesc =
 		index_beginscan_parallel(node->ss.ss_currentRelation,
 								 node->iss_RelationDesc,
-								 0, /* flags */
+								 ScanRelIsReadOnly(&node->ss) ?
+								 SO_HINT_REL_READ_ONLY : 0,
 								 node->iss_Instrument,
 								 node->iss_NumScanKeys,
 								 node->iss_NumOrderByKeys,
diff --git a/src/backend/executor/nodeSamplescan.c b/src/backend/executor/nodeSamplescan.c
index cf4dd6a16b4..b6a02072da5 100644
--- a/src/backend/executor/nodeSamplescan.c
+++ b/src/backend/executor/nodeSamplescan.c
@@ -292,9 +292,12 @@ tablesample_init(SampleScanState *scanstate)
 	/* Now we can create or reset the HeapScanDesc */
 	if (scanstate->ss.ss_currentScanDesc == NULL)
 	{
+		uint32		flags = ScanRelIsReadOnly(&scanstate->ss) ?
+			SO_HINT_REL_READ_ONLY : 0;
+
 		scanstate->ss.ss_currentScanDesc =
 			table_beginscan_sampling(scanstate->ss.ss_currentRelation,
-									 0,
+									 flags,
 									 scanstate->ss.ps.state->es_snapshot,
 									 0, NULL,
 									 scanstate->use_bulkread,
diff --git a/src/backend/executor/nodeSeqscan.c b/src/backend/executor/nodeSeqscan.c
index 376e877e87c..2d0993a83f4 100644
--- a/src/backend/executor/nodeSeqscan.c
+++ b/src/backend/executor/nodeSeqscan.c
@@ -65,12 +65,15 @@ SeqNext(SeqScanState *node)
 
 	if (scandesc == NULL)
 	{
+		uint32		flags = ScanRelIsReadOnly(&node->ss) ?
+			SO_HINT_REL_READ_ONLY : 0;
+
 		/*
 		 * We reach here if the scan is not parallel, or if we're serially
 		 * executing a scan that was planned to be parallel.
 		 */
 		scandesc = table_beginscan(node->ss.ss_currentRelation,
-								   0, estate->es_snapshot,
+								   flags, estate->es_snapshot,
 								   0, NULL);
 		node->ss.ss_currentScanDesc = scandesc;
 	}
@@ -368,14 +371,17 @@ ExecSeqScanInitializeDSM(SeqScanState *node,
 {
 	EState	   *estate = node->ss.ps.state;
 	ParallelTableScanDesc pscan;
+	uint32		flags = ScanRelIsReadOnly(&node->ss) ?
+		SO_HINT_REL_READ_ONLY : 0;
 
 	pscan = shm_toc_allocate(pcxt->toc, node->pscan_len);
 	table_parallelscan_initialize(node->ss.ss_currentRelation,
 								  pscan,
 								  estate->es_snapshot);
 	shm_toc_insert(pcxt->toc, node->ss.ps.plan->plan_node_id, pscan);
+
 	node->ss.ss_currentScanDesc =
-		table_beginscan_parallel(node->ss.ss_currentRelation, 0, pscan);
+		table_beginscan_parallel(node->ss.ss_currentRelation, flags, pscan);
 }
 
 /* ----------------------------------------------------------------
@@ -405,8 +411,10 @@ ExecSeqScanInitializeWorker(SeqScanState *node,
 							ParallelWorkerContext *pwcxt)
 {
 	ParallelTableScanDesc pscan;
+	uint32		flags = ScanRelIsReadOnly(&node->ss) ?
+		SO_HINT_REL_READ_ONLY : 0;
 
 	pscan = shm_toc_lookup(pwcxt->toc, node->ss.ps.plan->plan_node_id, false);
 	node->ss.ss_currentScanDesc =
-		table_beginscan_parallel(node->ss.ss_currentRelation, 0, pscan);
+		table_beginscan_parallel(node->ss.ss_currentRelation, flags, pscan);
 }
diff --git a/src/backend/executor/nodeTidrangescan.c b/src/backend/executor/nodeTidrangescan.c
index bacd7aa5bc4..05ed5364238 100644
--- a/src/backend/executor/nodeTidrangescan.c
+++ b/src/backend/executor/nodeTidrangescan.c
@@ -242,8 +242,11 @@ TidRangeNext(TidRangeScanState *node)
 
 		if (scandesc == NULL)
 		{
+			uint32		flags = ScanRelIsReadOnly(&node->ss) ?
+				SO_HINT_REL_READ_ONLY : 0;
+
 			scandesc = table_beginscan_tidrange(node->ss.ss_currentRelation,
-												0,
+												flags,
 												estate->es_snapshot,
 												&node->trss_mintid,
 												&node->trss_maxtid);
@@ -453,15 +456,18 @@ ExecTidRangeScanInitializeDSM(TidRangeScanState *node, ParallelContext *pcxt)
 {
 	EState	   *estate = node->ss.ps.state;
 	ParallelTableScanDesc pscan;
+	uint32		flags = ScanRelIsReadOnly(&node->ss) ?
+		SO_HINT_REL_READ_ONLY : 0;
 
 	pscan = shm_toc_allocate(pcxt->toc, node->trss_pscanlen);
 	table_parallelscan_initialize(node->ss.ss_currentRelation,
 								  pscan,
 								  estate->es_snapshot);
 	shm_toc_insert(pcxt->toc, node->ss.ps.plan->plan_node_id, pscan);
+
 	node->ss.ss_currentScanDesc =
 		table_beginscan_parallel_tidrange(node->ss.ss_currentRelation,
-										  0, pscan);
+										  flags, pscan);
 }
 
 /* ----------------------------------------------------------------
@@ -491,9 +497,12 @@ ExecTidRangeScanInitializeWorker(TidRangeScanState *node,
 								 ParallelWorkerContext *pwcxt)
 {
 	ParallelTableScanDesc pscan;
+	uint32		flags = ScanRelIsReadOnly(&node->ss) ?
+		SO_HINT_REL_READ_ONLY : 0;
 
 	pscan = shm_toc_lookup(pwcxt->toc, node->ss.ps.plan->plan_node_id, false);
+
 	node->ss.ss_currentScanDesc =
 		table_beginscan_parallel_tidrange(node->ss.ss_currentRelation,
-										  0, pscan);
+										  flags, pscan);
 }
diff --git a/src/include/access/tableam.h b/src/include/access/tableam.h
index e1f90f2b6a7..a8fd8f0d45c 100644
--- a/src/include/access/tableam.h
+++ b/src/include/access/tableam.h
@@ -63,6 +63,9 @@ typedef enum ScanOptions
 
 	/* unregister snapshot at scan end? */
 	SO_TEMP_SNAPSHOT = 1 << 9,
+
+	/* set if the query doesn't modify the relation */
+	SO_HINT_REL_READ_ONLY = 1 << 10,
 }			ScanOptions;
 
 /*
diff --git a/src/include/executor/executor.h b/src/include/executor/executor.h
index 07f4b1f7490..7979a17e4ec 100644
--- a/src/include/executor/executor.h
+++ b/src/include/executor/executor.h
@@ -690,6 +690,8 @@ extern void ExecCreateScanSlotFromOuterPlan(EState *estate,
 
 extern bool ExecRelationIsTargetRelation(EState *estate, Index scanrelid);
 
+extern bool ScanRelIsReadOnly(ScanState *ss);
+
 extern Relation ExecOpenScanRelation(EState *estate, Index scanrelid, int eflags);
 
 extern void ExecInitRangeTable(EState *estate, List *rangeTable, List *permInfos,
-- 
2.43.0