v34-0012-Pass-down-information-on-table-modification-to-s.patch

From 8205b2d7da0c3ad3cbc5cead336ced677996b37d Mon Sep 17 00:00:00 2001
From: Melanie Plageman <melanieplageman@gmail.com>
Date: Wed, 3 Dec 2025 15:12:18 -0500
Subject: [PATCH v34 12/14] 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: 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
---
 contrib/pgrowlocks/pgrowlocks.c           |  2 +-
 src/backend/access/brin/brin.c            |  3 ++-
 src/backend/access/gin/gininsert.c        |  3 ++-
 src/backend/access/heap/heapam_handler.c  |  7 +++---
 src/backend/access/index/genam.c          |  4 ++--
 src/backend/access/index/indexam.c        |  6 +++---
 src/backend/access/nbtree/nbtsort.c       |  2 +-
 src/backend/access/table/tableam.c        |  7 +++---
 src/backend/commands/constraint.c         |  2 +-
 src/backend/commands/copyto.c             |  2 +-
 src/backend/commands/tablecmds.c          |  8 +++----
 src/backend/commands/typecmds.c           |  4 ++--
 src/backend/executor/execIndexing.c       |  2 +-
 src/backend/executor/execReplication.c    |  8 +++----
 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/backend/partitioning/partbounds.c     |  2 +-
 src/backend/utils/adt/selfuncs.c          |  2 +-
 src/include/access/genam.h                |  2 +-
 src/include/access/heapam.h               |  6 ++++++
 src/include/access/tableam.h              | 19 ++++++++++-------
 23 files changed, 107 insertions(+), 46 deletions(-)

diff --git a/contrib/pgrowlocks/pgrowlocks.c b/contrib/pgrowlocks/pgrowlocks.c
index f88269332b6..27f01d8055f 100644
--- a/contrib/pgrowlocks/pgrowlocks.c
+++ b/contrib/pgrowlocks/pgrowlocks.c
@@ -114,7 +114,7 @@ pgrowlocks(PG_FUNCTION_ARGS)
 					   RelationGetRelationName(rel));
 
 	/* Scan the relation */
-	scan = table_beginscan(rel, GetActiveSnapshot(), 0, NULL);
+	scan = table_beginscan(rel, GetActiveSnapshot(), 0, NULL, 0);
 	hscan = (HeapScanDesc) scan;
 
 	attinmeta = TupleDescGetAttInMetadata(rsinfo->setDesc);
diff --git a/src/backend/access/brin/brin.c b/src/backend/access/brin/brin.c
index 6887e421442..4d9684b1b19 100644
--- a/src/backend/access/brin/brin.c
+++ b/src/backend/access/brin/brin.c
@@ -2843,7 +2843,8 @@ _brin_parallel_scan_and_build(BrinBuildState *state,
 	indexInfo->ii_Concurrent = brinshared->isconcurrent;
 
 	scan = table_beginscan_parallel(heap,
-									ParallelTableScanFromBrinShared(brinshared));
+									ParallelTableScanFromBrinShared(brinshared),
+									0);
 
 	reltuples = table_index_build_scan(heap, index, indexInfo, true, true,
 									   brinbuildCallbackParallel, state, scan);
diff --git a/src/backend/access/gin/gininsert.c b/src/backend/access/gin/gininsert.c
index 0d63fb4ba27..f02d6df40a2 100644
--- a/src/backend/access/gin/gininsert.c
+++ b/src/backend/access/gin/gininsert.c
@@ -2059,7 +2059,8 @@ _gin_parallel_scan_and_build(GinBuildState *state,
 	indexInfo->ii_Concurrent = ginshared->isconcurrent;
 
 	scan = table_beginscan_parallel(heap,
-									ParallelTableScanFromGinBuildShared(ginshared));
+									ParallelTableScanFromGinBuildShared(ginshared),
+									0);
 
 	reltuples = table_index_build_scan(heap, index, indexInfo, true, progress,
 									   ginBuildCallbackParallel, state, scan);
diff --git a/src/backend/access/heap/heapam_handler.c b/src/backend/access/heap/heapam_handler.c
index da4ae236ca8..6ce4350c2c8 100644
--- a/src/backend/access/heap/heapam_handler.c
+++ b/src/backend/access/heap/heapam_handler.c
@@ -79,12 +79,13 @@ heapam_slot_callbacks(Relation relation)
  */
 
 static IndexFetchTableData *
-heapam_index_fetch_begin(Relation rel)
+heapam_index_fetch_begin(Relation rel, uint32 flags)
 {
 	IndexFetchHeapData *hscan = palloc0_object(IndexFetchHeapData);
 
 	hscan->xs_base.rel = rel;
 	hscan->xs_cbuf = InvalidBuffer;
+	hscan->modifies_base_rel = !(flags & SO_HINT_REL_READ_ONLY);
 
 	return &hscan->xs_base;
 }
@@ -753,7 +754,7 @@ heapam_relation_copy_for_cluster(Relation OldHeap, Relation NewHeap,
 
 		tableScan = NULL;
 		heapScan = NULL;
-		indexScan = index_beginscan(OldHeap, OldIndex, SnapshotAny, NULL, 0, 0);
+		indexScan = index_beginscan(OldHeap, OldIndex, SnapshotAny, NULL, 0, 0, 0);
 		index_rescan(indexScan, NULL, 0, NULL, 0);
 	}
 	else
@@ -762,7 +763,7 @@ heapam_relation_copy_for_cluster(Relation OldHeap, Relation NewHeap,
 		pgstat_progress_update_param(PROGRESS_CLUSTER_PHASE,
 									 PROGRESS_CLUSTER_PHASE_SEQ_SCAN_HEAP);
 
-		tableScan = table_beginscan(OldHeap, SnapshotAny, 0, (ScanKey) NULL);
+		tableScan = table_beginscan(OldHeap, SnapshotAny, 0, (ScanKey) NULL, 0);
 		heapScan = (HeapScanDesc) tableScan;
 		indexScan = NULL;
 
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index a29be6f467b..5ac7d22e49f 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -447,7 +447,7 @@ systable_beginscan(Relation heapRelation,
 		}
 
 		sysscan->iscan = index_beginscan(heapRelation, irel,
-										 snapshot, NULL, nkeys, 0);
+										 snapshot, NULL, nkeys, 0, 0);
 		index_rescan(sysscan->iscan, idxkey, nkeys, NULL, 0);
 		sysscan->scan = NULL;
 
@@ -708,7 +708,7 @@ systable_beginscan_ordered(Relation heapRelation,
 	}
 
 	sysscan->iscan = index_beginscan(heapRelation, indexRelation,
-									 snapshot, NULL, nkeys, 0);
+									 snapshot, NULL, nkeys, 0, 0);
 	index_rescan(sysscan->iscan, idxkey, nkeys, NULL, 0);
 	sysscan->scan = NULL;
 
diff --git a/src/backend/access/index/indexam.c b/src/backend/access/index/indexam.c
index 4ed0508c605..4df56087841 100644
--- a/src/backend/access/index/indexam.c
+++ b/src/backend/access/index/indexam.c
@@ -257,7 +257,7 @@ index_beginscan(Relation heapRelation,
 				Relation indexRelation,
 				Snapshot snapshot,
 				IndexScanInstrumentation *instrument,
-				int nkeys, int norderbys)
+				int nkeys, int norderbys, uint32 flags)
 {
 	IndexScanDesc scan;
 
@@ -284,7 +284,7 @@ index_beginscan(Relation heapRelation,
 	scan->instrument = instrument;
 
 	/* prepare to fetch index matches from table */
-	scan->xs_heapfetch = table_index_fetch_begin(heapRelation);
+	scan->xs_heapfetch = table_index_fetch_begin(heapRelation, flags);
 
 	return scan;
 }
@@ -615,7 +615,7 @@ index_beginscan_parallel(Relation heaprel, Relation indexrel,
 	scan->instrument = instrument;
 
 	/* prepare to fetch index matches from table */
-	scan->xs_heapfetch = table_index_fetch_begin(heaprel);
+	scan->xs_heapfetch = table_index_fetch_begin(heaprel, 0);
 
 	return scan;
 }
diff --git a/src/backend/access/nbtree/nbtsort.c b/src/backend/access/nbtree/nbtsort.c
index 90ab4e91b56..8ae54217f36 100644
--- a/src/backend/access/nbtree/nbtsort.c
+++ b/src/backend/access/nbtree/nbtsort.c
@@ -1925,7 +1925,7 @@ _bt_parallel_scan_and_sort(BTSpool *btspool, BTSpool *btspool2,
 	indexInfo = BuildIndexInfo(btspool->index);
 	indexInfo->ii_Concurrent = btshared->isconcurrent;
 	scan = table_beginscan_parallel(btspool->heap,
-									ParallelTableScanFromBTShared(btshared));
+									ParallelTableScanFromBTShared(btshared), 0);
 	reltuples = table_index_build_scan(btspool->heap, btspool->index, indexInfo,
 									   true, progress, _bt_build_callback,
 									   &buildstate, scan);
diff --git a/src/backend/access/table/tableam.c b/src/backend/access/table/tableam.c
index 87491796523..2ff29b6e40b 100644
--- a/src/backend/access/table/tableam.c
+++ b/src/backend/access/table/tableam.c
@@ -163,10 +163,11 @@ table_parallelscan_initialize(Relation rel, ParallelTableScanDesc pscan,
 }
 
 TableScanDesc
-table_beginscan_parallel(Relation relation, ParallelTableScanDesc pscan)
+table_beginscan_parallel(Relation relation, ParallelTableScanDesc pscan, uint32 flags)
 {
 	Snapshot	snapshot;
-	uint32		flags = SO_TYPE_SEQSCAN |
+
+	flags |= SO_TYPE_SEQSCAN |
 		SO_ALLOW_STRAT | SO_ALLOW_SYNC | SO_ALLOW_PAGEMODE;
 
 	Assert(RelFileLocatorEquals(relation->rd_locator, pscan->phs_locator));
@@ -248,7 +249,7 @@ table_index_fetch_tuple_check(Relation rel,
 	bool		found;
 
 	slot = table_slot_create(rel, NULL);
-	scan = table_index_fetch_begin(rel);
+	scan = table_index_fetch_begin(rel, 0);
 	found = table_index_fetch_tuple(scan, tid, snapshot, slot, &call_again,
 									all_dead);
 	table_index_fetch_end(scan);
diff --git a/src/backend/commands/constraint.c b/src/backend/commands/constraint.c
index cc11c47b6f2..37cfbd63938 100644
--- a/src/backend/commands/constraint.c
+++ b/src/backend/commands/constraint.c
@@ -106,7 +106,7 @@ unique_key_recheck(PG_FUNCTION_ARGS)
 	 */
 	tmptid = checktid;
 	{
-		IndexFetchTableData *scan = table_index_fetch_begin(trigdata->tg_relation);
+		IndexFetchTableData *scan = table_index_fetch_begin(trigdata->tg_relation, 0);
 		bool		call_again = false;
 
 		if (!table_index_fetch_tuple(scan, &tmptid, SnapshotSelf, slot,
diff --git a/src/backend/commands/copyto.c b/src/backend/commands/copyto.c
index 4ab4a3893d5..4261baf4a41 100644
--- a/src/backend/commands/copyto.c
+++ b/src/backend/commands/copyto.c
@@ -1156,7 +1156,7 @@ CopyRelationTo(CopyToState cstate, Relation rel, Relation root_rel, uint64 *proc
 	AttrMap    *map = NULL;
 	TupleTableSlot *root_slot = NULL;
 
-	scandesc = table_beginscan(rel, GetActiveSnapshot(), 0, NULL);
+	scandesc = table_beginscan(rel, GetActiveSnapshot(), 0, NULL, 0);
 	slot = table_slot_create(rel, NULL);
 
 	/*
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index f976c0e5c7e..eb35dbbc853 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -6378,7 +6378,7 @@ ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap)
 		 * checking all the constraints.
 		 */
 		snapshot = RegisterSnapshot(GetLatestSnapshot());
-		scan = table_beginscan(oldrel, snapshot, 0, NULL);
+		scan = table_beginscan(oldrel, snapshot, 0, NULL, 0);
 
 		/*
 		 * Switch to per-tuple memory context and reset it for each tuple
@@ -13768,7 +13768,7 @@ validateForeignKeyConstraint(char *conname,
 	 */
 	snapshot = RegisterSnapshot(GetLatestSnapshot());
 	slot = table_slot_create(rel, NULL);
-	scan = table_beginscan(rel, snapshot, 0, NULL);
+	scan = table_beginscan(rel, snapshot, 0, NULL, 0);
 
 	perTupCxt = AllocSetContextCreate(CurrentMemoryContext,
 									  "validateForeignKeyConstraint",
@@ -22626,7 +22626,7 @@ MergePartitionsMoveRows(List **wqueue, List *mergingPartitions, Relation newPart
 
 		/* Scan through the rows. */
 		snapshot = RegisterSnapshot(GetLatestSnapshot());
-		scan = table_beginscan(mergingPartition, snapshot, 0, NULL);
+		scan = table_beginscan(mergingPartition, snapshot, 0, NULL, 0);
 
 		/*
 		 * Switch to per-tuple memory context and reset it for each tuple
@@ -23090,7 +23090,7 @@ SplitPartitionMoveRows(List **wqueue, Relation rel, Relation splitRel,
 
 	/* Scan through the rows. */
 	snapshot = RegisterSnapshot(GetLatestSnapshot());
-	scan = table_beginscan(splitRel, snapshot, 0, NULL);
+	scan = table_beginscan(splitRel, snapshot, 0, NULL, 0);
 
 	/*
 	 * Switch to per-tuple memory context and reset it for each tuple
diff --git a/src/backend/commands/typecmds.c b/src/backend/commands/typecmds.c
index 288edb25f2f..34ff8d041f1 100644
--- a/src/backend/commands/typecmds.c
+++ b/src/backend/commands/typecmds.c
@@ -3179,7 +3179,7 @@ validateDomainNotNullConstraint(Oid domainoid)
 
 		/* Scan all tuples in this relation */
 		snapshot = RegisterSnapshot(GetLatestSnapshot());
-		scan = table_beginscan(testrel, snapshot, 0, NULL);
+		scan = table_beginscan(testrel, snapshot, 0, NULL, 0);
 		slot = table_slot_create(testrel, NULL);
 		while (table_scan_getnextslot(scan, ForwardScanDirection, slot))
 		{
@@ -3260,7 +3260,7 @@ validateDomainCheckConstraint(Oid domainoid, const char *ccbin, LOCKMODE lockmod
 
 		/* Scan all tuples in this relation */
 		snapshot = RegisterSnapshot(GetLatestSnapshot());
-		scan = table_beginscan(testrel, snapshot, 0, NULL);
+		scan = table_beginscan(testrel, snapshot, 0, NULL, 0);
 		slot = table_slot_create(testrel, NULL);
 		while (table_scan_getnextslot(scan, ForwardScanDirection, slot))
 		{
diff --git a/src/backend/executor/execIndexing.c b/src/backend/executor/execIndexing.c
index 6ae0f959592..6d3e9d2f311 100644
--- a/src/backend/executor/execIndexing.c
+++ b/src/backend/executor/execIndexing.c
@@ -816,7 +816,7 @@ check_exclusion_or_unique_constraint(Relation heap, Relation index,
 retry:
 	conflict = false;
 	found_self = false;
-	index_scan = index_beginscan(heap, index, &DirtySnapshot, NULL, indnkeyatts, 0);
+	index_scan = index_beginscan(heap, index, &DirtySnapshot, NULL, indnkeyatts, 0, 0);
 	index_rescan(index_scan, scankeys, indnkeyatts, NULL, 0);
 
 	while (index_getnext_slot(index_scan, ForwardScanDirection, existing_slot))
diff --git a/src/backend/executor/execReplication.c b/src/backend/executor/execReplication.c
index 72f2bff7708..4c965a35e05 100644
--- a/src/backend/executor/execReplication.c
+++ b/src/backend/executor/execReplication.c
@@ -205,7 +205,7 @@ RelationFindReplTupleByIndex(Relation rel, Oid idxoid,
 	skey_attoff = build_replindex_scan_key(skey, rel, idxrel, searchslot);
 
 	/* Start an index scan. */
-	scan = index_beginscan(rel, idxrel, &snap, NULL, skey_attoff, 0);
+	scan = index_beginscan(rel, idxrel, &snap, NULL, skey_attoff, 0, 0);
 
 retry:
 	found = false;
@@ -383,7 +383,7 @@ RelationFindReplTupleSeq(Relation rel, LockTupleMode lockmode,
 
 	/* Start a heap scan. */
 	InitDirtySnapshot(snap);
-	scan = table_beginscan(rel, &snap, 0, NULL);
+	scan = table_beginscan(rel, &snap, 0, NULL, 0);
 	scanslot = table_slot_create(rel, NULL);
 
 retry:
@@ -602,7 +602,7 @@ RelationFindDeletedTupleInfoSeq(Relation rel, TupleTableSlot *searchslot,
 	 * not yet committed or those just committed prior to the scan are
 	 * excluded in update_most_recent_deletion_info().
 	 */
-	scan = table_beginscan(rel, SnapshotAny, 0, NULL);
+	scan = table_beginscan(rel, SnapshotAny, 0, NULL, 0);
 	scanslot = table_slot_create(rel, NULL);
 
 	table_rescan(scan, NULL);
@@ -666,7 +666,7 @@ RelationFindDeletedTupleInfoByIndex(Relation rel, Oid idxoid,
 	 * not yet committed or those just committed prior to the scan are
 	 * excluded in update_most_recent_deletion_info().
 	 */
-	scan = index_beginscan(rel, idxrel, SnapshotAny, NULL, skey_attoff, 0);
+	scan = index_beginscan(rel, idxrel, SnapshotAny, NULL, skey_attoff, 0, 0);
 
 	index_rescan(scan, skey, skey_attoff, NULL, 0);
 
diff --git a/src/backend/executor/nodeBitmapHeapscan.c b/src/backend/executor/nodeBitmapHeapscan.c
index c68c26cbf38..1017676fce0 100644
--- a/src/backend/executor/nodeBitmapHeapscan.c
+++ b/src/backend/executor/nodeBitmapHeapscan.c
@@ -103,11 +103,18 @@ 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);
+							   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 c2d09374517..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);
+								   node->ioss_NumOrderByKeys,
+								   flags);
 
 		node->ioss_ScanDesc = scandesc;
 
diff --git a/src/backend/executor/nodeIndexscan.c b/src/backend/executor/nodeIndexscan.c
index a616abff04c..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);
+								   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);
+								   node->iss_NumOrderByKeys,
+								   flags);
 
 		node->iss_ScanDesc = scandesc;
 
diff --git a/src/backend/executor/nodeSeqscan.c b/src/backend/executor/nodeSeqscan.c
index af3c788ce8b..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, 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);
+		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);
+		table_beginscan_parallel(node->ss.ss_currentRelation,
+								 pscan,
+								 flags);
 }
diff --git a/src/backend/partitioning/partbounds.c b/src/backend/partitioning/partbounds.c
index 0ca312ac27d..b7c4e6d1071 100644
--- a/src/backend/partitioning/partbounds.c
+++ b/src/backend/partitioning/partbounds.c
@@ -3362,7 +3362,7 @@ check_default_partition_contents(Relation parent, Relation default_rel,
 		econtext = GetPerTupleExprContext(estate);
 		snapshot = RegisterSnapshot(GetLatestSnapshot());
 		tupslot = table_slot_create(part_rel, &estate->es_tupleTable);
-		scan = table_beginscan(part_rel, snapshot, 0, NULL);
+		scan = table_beginscan(part_rel, snapshot, 0, NULL, 0);
 
 		/*
 		 * Switch to per-tuple memory context and reset it for each tuple
diff --git a/src/backend/utils/adt/selfuncs.c b/src/backend/utils/adt/selfuncs.c
index 29fec655593..ac181853225 100644
--- a/src/backend/utils/adt/selfuncs.c
+++ b/src/backend/utils/adt/selfuncs.c
@@ -7181,7 +7181,7 @@ get_actual_variable_endpoint(Relation heapRel,
 
 	index_scan = index_beginscan(heapRel, indexRel,
 								 &SnapshotNonVacuumable, NULL,
-								 1, 0);
+								 1, 0, 0);
 	/* Set it up for index-only scan */
 	index_scan->xs_want_itup = true;
 	index_rescan(index_scan, scankeys, 1, NULL, 0);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index 4c0429cc613..3934fa44793 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -156,7 +156,7 @@ extern IndexScanDesc index_beginscan(Relation heapRelation,
 									 Relation indexRelation,
 									 Snapshot snapshot,
 									 IndexScanInstrumentation *instrument,
-									 int nkeys, int norderbys);
+									 int nkeys, int norderbys, uint32 flags);
 extern IndexScanDesc index_beginscan_bitmap(Relation indexRelation,
 											Snapshot snapshot,
 											IndexScanInstrumentation *instrument,
diff --git a/src/include/access/heapam.h b/src/include/access/heapam.h
index 05ef8d8cd5e..6d54781609a 100644
--- a/src/include/access/heapam.h
+++ b/src/include/access/heapam.h
@@ -119,6 +119,12 @@ typedef struct IndexFetchHeapData
 
 	Buffer		xs_cbuf;		/* current heap buffer in scan, if any */
 	/* NB: if xs_cbuf is not InvalidBuffer, we hold a pin on that buffer */
+
+	/*
+	 * 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 c9fa9f259cd..fb2a54b010d 100644
--- a/src/include/access/tableam.h
+++ b/src/include/access/tableam.h
@@ -63,6 +63,8 @@ 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;
 
 /*
@@ -420,7 +422,7 @@ typedef struct TableAmRoutine
 	 *
 	 * Tuples for an index scan can then be fetched via index_fetch_tuple.
 	 */
-	struct IndexFetchTableData *(*index_fetch_begin) (Relation rel);
+	struct IndexFetchTableData *(*index_fetch_begin) (Relation rel, uint32 flags);
 
 	/*
 	 * Reset index fetch. Typically this will release cross index fetch
@@ -873,9 +875,9 @@ extern TupleTableSlot *table_slot_create(Relation relation, List **reglist);
  */
 static inline TableScanDesc
 table_beginscan(Relation rel, Snapshot snapshot,
-				int nkeys, ScanKeyData *key)
+				int nkeys, ScanKeyData *key, uint32 flags)
 {
-	uint32		flags = SO_TYPE_SEQSCAN |
+	flags |= SO_TYPE_SEQSCAN |
 		SO_ALLOW_STRAT | SO_ALLOW_SYNC | SO_ALLOW_PAGEMODE;
 
 	return rel->rd_tableam->scan_begin(rel, snapshot, nkeys, key, NULL, flags);
@@ -918,9 +920,9 @@ table_beginscan_strat(Relation rel, Snapshot snapshot,
  */
 static inline TableScanDesc
 table_beginscan_bm(Relation rel, Snapshot snapshot,
-				   int nkeys, ScanKeyData *key)
+				   int nkeys, ScanKeyData *key, uint32 flags)
 {
-	uint32		flags = SO_TYPE_BITMAPSCAN | SO_ALLOW_PAGEMODE;
+	flags |= SO_TYPE_BITMAPSCAN | SO_ALLOW_PAGEMODE;
 
 	return rel->rd_tableam->scan_begin(rel, snapshot, nkeys, key,
 									   NULL, flags);
@@ -1127,7 +1129,8 @@ extern void table_parallelscan_initialize(Relation rel,
  * Caller must hold a suitable lock on the relation.
  */
 extern TableScanDesc table_beginscan_parallel(Relation relation,
-											  ParallelTableScanDesc pscan);
+											  ParallelTableScanDesc pscan,
+											  uint32 flags);
 
 /*
  * Begin a parallel tid range scan. `pscan` needs to have been initialized
@@ -1163,9 +1166,9 @@ table_parallelscan_reinitialize(Relation rel, ParallelTableScanDesc pscan)
  * Tuples for an index scan can then be fetched via table_index_fetch_tuple().
  */
 static inline IndexFetchTableData *
-table_index_fetch_begin(Relation rel)
+table_index_fetch_begin(Relation rel, uint32 flags)
 {
-	return rel->rd_tableam->index_fetch_begin(rel);
+	return rel->rd_tableam->index_fetch_begin(rel, flags);
 }
 
 /*
-- 
2.43.0