v37-0012-Pass-down-information-on-table-modification-to-s.patch

From 1a3685e4cf28fa0668861e3e5b25cfa7cb216c85 Mon Sep 17 00:00:00 2001
From: Melanie Plageman <melanieplageman@gmail.com>
Date: Mon, 2 Mar 2026 16:31:33 -0500
Subject: [PATCH v37 12/15] Pass down information on table modification to scan
 node

Pass down information to sequential scan, index [only] scan, and bitmap
table 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/access/heap/heapam_handler.c  |  1 +
 src/backend/executor/nodeBitmapHeapscan.c |  9 +++++++-
 src/backend/executor/nodeIndexonlyscan.c  |  9 +++++++-
 src/backend/executor/nodeIndexscan.c      | 18 ++++++++++++++--
 src/backend/executor/nodeSeqscan.c        | 26 ++++++++++++++++++++---
 src/include/access/heapam.h               |  6 ++++++
 src/include/access/tableam.h              |  3 +++
 7 files changed, 65 insertions(+), 7 deletions(-)

diff --git a/src/backend/access/heap/heapam_handler.c b/src/backend/access/heap/heapam_handler.c
index f4b169e2c04..098ca32fa84 100644
--- a/src/backend/access/heap/heapam_handler.c
+++ b/src/backend/access/heap/heapam_handler.c
@@ -86,6 +86,7 @@ heapam_index_fetch_begin(Relation rel, uint32 flags)
 	hscan->xs_base.rel = rel;
 	hscan->xs_cbuf = InvalidBuffer;
 	hscan->xs_vmbuffer = InvalidBuffer;
+	hscan->modifies_base_rel = !(flags & SO_HINT_REL_READ_ONLY);
 
 	return &hscan->xs_base;
 }
diff --git a/src/backend/executor/nodeBitmapHeapscan.c b/src/backend/executor/nodeBitmapHeapscan.c
index b3b6da3d7e4..9bcf9a68183 100644
--- a/src/backend/executor/nodeBitmapHeapscan.c
+++ b/src/backend/executor/nodeBitmapHeapscan.c
@@ -104,11 +104,18 @@ BitmapTableScanSetup(BitmapHeapScanState *node)
 	 */
 	if (!node->ss.ss_currentScanDesc)
 	{
+		uint32		flags = 0;
+
+		if (!bms_is_member(((Scan *) node->ss.ps.plan)->scanrelid,
+						   node->ss.ps.state->es_modified_relids))
+			flags = SO_HINT_REL_READ_ONLY;
+
 		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 cf4d9a4f832..2fe724a323f 100644
--- a/src/backend/executor/nodeIndexonlyscan.c
+++ b/src/backend/executor/nodeIndexonlyscan.c
@@ -84,6 +84,12 @@ IndexOnlyNext(IndexOnlyScanState *node)
 
 	if (scandesc == NULL)
 	{
+		uint32		flags = 0;
+
+		if (!bms_is_member(((Scan *) node->ss.ps.plan)->scanrelid,
+						   estate->es_modified_relids))
+			flags = SO_HINT_REL_READ_ONLY;
+
 		/*
 		 * 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
@@ -94,7 +100,8 @@ IndexOnlyNext(IndexOnlyScanState *node)
 								   estate->es_snapshot,
 								   &node->ioss_Instrument,
 								   node->ioss_NumScanKeys,
-								   node->ioss_NumOrderByKeys, 0);
+								   node->ioss_NumOrderByKeys,
+								   flags);
 
 		node->ioss_ScanDesc = scandesc;
 
diff --git a/src/backend/executor/nodeIndexscan.c b/src/backend/executor/nodeIndexscan.c
index a7af2f6628a..8730dab7469 100644
--- a/src/backend/executor/nodeIndexscan.c
+++ b/src/backend/executor/nodeIndexscan.c
@@ -102,6 +102,12 @@ IndexNext(IndexScanState *node)
 
 	if (scandesc == NULL)
 	{
+		uint32		flags = 0;
+
+		if (!bms_is_member(((Scan *) node->ss.ps.plan)->scanrelid,
+						   estate->es_modified_relids))
+			flags = SO_HINT_REL_READ_ONLY;
+
 		/*
 		 * 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.
@@ -111,7 +117,8 @@ IndexNext(IndexScanState *node)
 								   estate->es_snapshot,
 								   &node->iss_Instrument,
 								   node->iss_NumScanKeys,
-								   node->iss_NumOrderByKeys, 0);
+								   node->iss_NumOrderByKeys,
+								   flags);
 
 		node->iss_ScanDesc = scandesc;
 
@@ -198,6 +205,12 @@ IndexNextWithReorder(IndexScanState *node)
 
 	if (scandesc == NULL)
 	{
+		uint32		flags = 0;
+
+		if (!bms_is_member(((Scan *) node->ss.ps.plan)->scanrelid,
+						   estate->es_modified_relids))
+			flags = SO_HINT_REL_READ_ONLY;
+
 		/*
 		 * 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.
@@ -207,7 +220,8 @@ IndexNextWithReorder(IndexScanState *node)
 								   estate->es_snapshot,
 								   &node->iss_Instrument,
 								   node->iss_NumScanKeys,
-								   node->iss_NumOrderByKeys, 0);
+								   node->iss_NumOrderByKeys,
+								   flags);
 
 		node->iss_ScanDesc = scandesc;
 
diff --git a/src/backend/executor/nodeSeqscan.c b/src/backend/executor/nodeSeqscan.c
index d9d7ec0516a..336354922a2 100644
--- a/src/backend/executor/nodeSeqscan.c
+++ b/src/backend/executor/nodeSeqscan.c
@@ -65,13 +65,20 @@ SeqNext(SeqScanState *node)
 
 	if (scandesc == NULL)
 	{
+		uint32		flags = 0;
+
+		if (!bms_is_member(((Scan *) node->ss.ps.plan)->scanrelid,
+						   estate->es_modified_relids))
+			flags = SO_HINT_REL_READ_ONLY;
+
 		/*
 		 * 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;
 	}
 
@@ -367,14 +374,20 @@ ExecSeqScanInitializeDSM(SeqScanState *node,
 {
 	EState	   *estate = node->ss.ps.state;
 	ParallelTableScanDesc pscan;
+	uint32		flags = 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);
+	if (!bms_is_member(((Scan *) node->ss.ps.plan)->scanrelid,
+					   estate->es_modified_relids))
+		flags = SO_HINT_REL_READ_ONLY;
+
 	node->ss.ss_currentScanDesc =
-		table_beginscan_parallel(node->ss.ss_currentRelation, pscan, 0);
+		table_beginscan_parallel(node->ss.ss_currentRelation, pscan,
+								 flags);
 }
 
 /* ----------------------------------------------------------------
@@ -404,8 +417,15 @@ ExecSeqScanInitializeWorker(SeqScanState *node,
 							ParallelWorkerContext *pwcxt)
 {
 	ParallelTableScanDesc pscan;
+	uint32		flags = 0;
+
+	if (!bms_is_member(((Scan *) node->ss.ps.plan)->scanrelid,
+					   node->ss.ps.state->es_modified_relids))
+		flags = SO_HINT_REL_READ_ONLY;
 
 	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/include/access/heapam.h b/src/include/access/heapam.h
index f77a00291bb..caa5e9b4206 100644
--- a/src/include/access/heapam.h
+++ b/src/include/access/heapam.h
@@ -130,6 +130,12 @@ typedef struct IndexFetchHeapData
 
 	/* Current heap block's corresponding page in the visibility map */
 	Buffer		xs_vmbuffer;
+
+	/*
+	 * Some optimizations can only be performed if the query does not modify
+	 * the underlying relation. Track that here.
+	 */
+	bool		modifies_base_rel;
 } IndexFetchHeapData;
 
 /* Result codes for HeapTupleSatisfiesVacuum */
diff --git a/src/include/access/tableam.h b/src/include/access/tableam.h
index e881e4f82a0..51dfd122307 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;
 
 /*
-- 
2.43.0