v43-0008-Pass-down-information-on-table-modification-to-s.patch

From 1648a5f09de8bacd005d383469436f21a73ced7d Mon Sep 17 00:00:00 2001
From: Melanie Plageman <melanieplageman@gmail.com>
Date: Mon, 2 Mar 2026 16:31:33 -0500
Subject: [PATCH v43 08/10] 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/nodeBitmapHeapscan.c |  6 +++++-
 src/backend/executor/nodeIndexonlyscan.c  | 15 ++++++++++++---
 src/backend/executor/nodeIndexscan.c      | 18 ++++++++++++++----
 src/backend/executor/nodeSamplescan.c     |  5 ++++-
 src/backend/executor/nodeSeqscan.c        | 18 +++++++++++++++---
 src/backend/executor/nodeTidrangescan.c   | 15 ++++++++++++---
 src/include/access/tableam.h              |  3 +++
 src/include/executor/executor.h           | 10 ++++++++++
 8 files changed, 75 insertions(+), 15 deletions(-)

diff --git a/src/backend/executor/nodeBitmapHeapscan.c b/src/backend/executor/nodeBitmapHeapscan.c
index 324e2bed22c..aec92c868ac 100644
--- a/src/backend/executor/nodeBitmapHeapscan.c
+++ b/src/backend/executor/nodeBitmapHeapscan.c
@@ -144,11 +144,15 @@ 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,
 							   node->ss.ps.state->es_snapshot,
 							   0,
-							   NULL, 0);
+							   NULL,
+							   flags);
 	}
 
 	node->ss.ss_currentScanDesc->st.rs_tbmiterator = tbmiterator;
diff --git a/src/backend/executor/nodeIndexonlyscan.c b/src/backend/executor/nodeIndexonlyscan.c
index f733be0220c..de9db45322c 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,
@@ -795,7 +798,10 @@ ExecIndexOnlyScanInitializeDSM(IndexOnlyScanState *node,
 								 node->ioss_Instrument,
 								 node->ioss_NumScanKeys,
 								 node->ioss_NumOrderByKeys,
-								 piscan, 0);
+								 piscan,
+								 ScanRelIsReadOnly(&node->ss) ?
+								 SO_HINT_REL_READ_ONLY : 0);
+
 	node->ioss_ScanDesc->xs_want_itup = true;
 	node->ioss_VMBuffer = InvalidBuffer;
 
@@ -861,7 +867,10 @@ ExecIndexOnlyScanInitializeWorker(IndexOnlyScanState *node,
 								 node->ioss_Instrument,
 								 node->ioss_NumScanKeys,
 								 node->ioss_NumOrderByKeys,
-								 piscan, 0);
+								 piscan,
+								 ScanRelIsReadOnly(&node->ss) ?
+								 SO_HINT_REL_READ_ONLY : 0);
+
 	node->ioss_ScanDesc->xs_want_itup = true;
 
 	/*
diff --git a/src/backend/executor/nodeIndexscan.c b/src/backend/executor/nodeIndexscan.c
index 1a101df492b..9df4a699504 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,
@@ -1732,7 +1738,9 @@ ExecIndexScanInitializeDSM(IndexScanState *node,
 								 node->iss_Instrument,
 								 node->iss_NumScanKeys,
 								 node->iss_NumOrderByKeys,
-								 piscan, 0);
+								 piscan,
+								 ScanRelIsReadOnly(&node->ss) ?
+								 SO_HINT_REL_READ_ONLY : 0);
 
 	/*
 	 * If no run-time keys to calculate or they are ready, go ahead and pass
@@ -1796,7 +1804,9 @@ ExecIndexScanInitializeWorker(IndexScanState *node,
 								 node->iss_Instrument,
 								 node->iss_NumScanKeys,
 								 node->iss_NumOrderByKeys,
-								 piscan, 0);
+								 piscan,
+								 ScanRelIsReadOnly(&node->ss) ?
+								 SO_HINT_REL_READ_ONLY : 0);
 
 	/*
 	 * If no run-time keys to calculate or they are ready, go ahead and pass
diff --git a/src/backend/executor/nodeSamplescan.c b/src/backend/executor/nodeSamplescan.c
index cc6b23abee0..71c70e5e5c7 100644
--- a/src/backend/executor/nodeSamplescan.c
+++ b/src/backend/executor/nodeSamplescan.c
@@ -292,13 +292,16 @@ 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,
 									 scanstate->ss.ps.state->es_snapshot,
 									 0, NULL,
 									 scanstate->use_bulkread,
 									 allow_sync,
-									 scanstate->use_pagemode, 0);
+									 scanstate->use_pagemode, flags);
 	}
 	else
 	{
diff --git a/src/backend/executor/nodeSeqscan.c b/src/backend/executor/nodeSeqscan.c
index c2d9b7293de..79470e6b9b5 100644
--- a/src/backend/executor/nodeSeqscan.c
+++ b/src/backend/executor/nodeSeqscan.c
@@ -65,13 +65,17 @@ 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,
 								   estate->es_snapshot,
-								   0, NULL, 0);
+								   0, NULL, flags);
+
 		node->ss.ss_currentScanDesc = scandesc;
 	}
 
@@ -368,14 +372,18 @@ 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, pscan, 0);
+		table_beginscan_parallel(node->ss.ss_currentRelation, pscan,
+								 flags);
 }
 
 /* ----------------------------------------------------------------
@@ -405,8 +413,12 @@ 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, pscan, 0);
+		table_beginscan_parallel(node->ss.ss_currentRelation,
+								 pscan,
+								 flags);
 }
diff --git a/src/backend/executor/nodeTidrangescan.c b/src/backend/executor/nodeTidrangescan.c
index 994f70989bc..4257afd96ed 100644
--- a/src/backend/executor/nodeTidrangescan.c
+++ b/src/backend/executor/nodeTidrangescan.c
@@ -242,10 +242,13 @@ 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,
 												estate->es_snapshot,
 												&node->trss_mintid,
-												&node->trss_maxtid, 0);
+												&node->trss_maxtid, flags);
 			node->ss.ss_currentScanDesc = scandesc;
 		}
 		else
@@ -452,15 +455,18 @@ 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,
-										  pscan, 0);
+										  pscan, flags);
 }
 
 /* ----------------------------------------------------------------
@@ -490,9 +496,12 @@ 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,
-										  pscan, 0);
+										  pscan, flags);
 }
diff --git a/src/include/access/tableam.h b/src/include/access/tableam.h
index 8357d05d83b..487e38292fa 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..31c4192b67e 100644
--- a/src/include/executor/executor.h
+++ b/src/include/executor/executor.h
@@ -690,6 +690,16 @@ extern void ExecCreateScanSlotFromOuterPlan(EState *estate,
 
 extern bool ExecRelationIsTargetRelation(EState *estate, Index scanrelid);
 
+/*
+ * Return true if the scan node's relation is not modified by the query.
+ */
+static inline bool
+ScanRelIsReadOnly(ScanState *ss)
+{
+	return !bms_is_member(((Scan *) ss->ps.plan)->scanrelid,
+						  ss->ps.state->es_plannedstmt->modifiedRelids);
+}
+
 extern Relation ExecOpenScanRelation(EState *estate, Index scanrelid, int eflags);
 
 extern void ExecInitRangeTable(EState *estate, List *rangeTable, List *permInfos,
-- 
2.43.0