v47-0004-Pass-down-information-on-table-modification-to-s.patch

From 975d619cbf3d9158a8134c9c62f8cf936290574b Mon Sep 17 00:00:00 2001
From: Melanie Plageman <melanieplageman@gmail.com>
Date: Mon, 2 Mar 2026 16:31:33 -0500
Subject: [PATCH v47 4/6] 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: Tomas Vondra <tomas@vondra.me>
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          | 21 +++++++++++++++++++++
 src/backend/executor/nodeBitmapHeapscan.c |  3 ++-
 src/backend/executor/nodeIndexonlyscan.c  |  9 ++++++---
 src/backend/executor/nodeIndexscan.c      | 12 ++++++++----
 src/backend/executor/nodeSamplescan.c     |  3 ++-
 src/backend/executor/nodeSeqscan.c        | 10 +++++++---
 src/backend/executor/nodeTidrangescan.c   | 11 ++++++++---
 src/include/access/tableam.h              |  3 +++
 src/include/executor/executor.h           |  2 ++
 9 files changed, 59 insertions(+), 15 deletions(-)

diff --git a/src/backend/executor/execUtils.c b/src/backend/executor/execUtils.c
index 36c5285d252..f090de49921 100644
--- a/src/backend/executor/execUtils.c
+++ b/src/backend/executor/execUtils.c
@@ -736,6 +736,27 @@ ExecRelationIsTargetRelation(EState *estate, Index scanrelid)
 	return bms_is_member(scanrelid, estate->es_plannedstmt->resultRelationRelids);
 }
 
+/*
+ * Return true if the scan node's relation is not modified by the query.
+ *
+ * This is not perfectly accurate. INSERT ... SELECT from the same table does
+ * not add the scan relation to resultRelationRelids, so it will be reported
+ * as read-only even though the query modifies it.
+ *
+ * Conversely, when any relation in the query has a modifying row mark, all
+ * other relations get a ROW_MARK_REFERENCE, causing them to be reported as
+ * not read-only even though they may only be read.
+ */
+bool
+ScanRelIsReadOnly(ScanState *ss)
+{
+	Index		scanrelid = ((Scan *) ss->ps.plan)->scanrelid;
+	PlannedStmt *pstmt = ss->ps.state->es_plannedstmt;
+
+	return !bms_is_member(scanrelid, pstmt->resultRelationRelids) &&
+		!bms_is_member(scanrelid, pstmt->rowMarkRelids);
+}
+
 /* ----------------------------------------------------------------
  *		ExecOpenScanRelation
  *
diff --git a/src/backend/executor/nodeBitmapHeapscan.c b/src/backend/executor/nodeBitmapHeapscan.c
index 69683d81527..73831aed451 100644
--- a/src/backend/executor/nodeBitmapHeapscan.c
+++ b/src/backend/executor/nodeBitmapHeapscan.c
@@ -149,7 +149,8 @@ BitmapTableScanSetup(BitmapHeapScanState *node)
 							   node->ss.ps.state->es_snapshot,
 							   0,
 							   NULL,
-							   SO_NONE);
+							   ScanRelIsReadOnly(&node->ss) ?
+							   SO_HINT_REL_READ_ONLY : SO_NONE);
 	}
 
 	node->ss.ss_currentScanDesc->st.rs_tbmiterator = tbmiterator;
diff --git a/src/backend/executor/nodeIndexonlyscan.c b/src/backend/executor/nodeIndexonlyscan.c
index 02df40f32c5..de6154fd541 100644
--- a/src/backend/executor/nodeIndexonlyscan.c
+++ b/src/backend/executor/nodeIndexonlyscan.c
@@ -96,7 +96,8 @@ IndexOnlyNext(IndexOnlyScanState *node)
 								   node->ioss_Instrument,
 								   node->ioss_NumScanKeys,
 								   node->ioss_NumOrderByKeys,
-								   SO_NONE);
+								   ScanRelIsReadOnly(&node->ss) ?
+								   SO_HINT_REL_READ_ONLY : SO_NONE);
 
 		node->ioss_ScanDesc = scandesc;
 
@@ -796,7 +797,8 @@ ExecIndexOnlyScanInitializeDSM(IndexOnlyScanState *node,
 								 node->ioss_NumScanKeys,
 								 node->ioss_NumOrderByKeys,
 								 piscan,
-								 SO_NONE);
+								 ScanRelIsReadOnly(&node->ss) ?
+								 SO_HINT_REL_READ_ONLY : SO_NONE);
 	node->ioss_ScanDesc->xs_want_itup = true;
 	node->ioss_VMBuffer = InvalidBuffer;
 
@@ -863,7 +865,8 @@ ExecIndexOnlyScanInitializeWorker(IndexOnlyScanState *node,
 								 node->ioss_NumScanKeys,
 								 node->ioss_NumOrderByKeys,
 								 piscan,
-								 SO_NONE);
+								 ScanRelIsReadOnly(&node->ss) ?
+								 SO_HINT_REL_READ_ONLY : SO_NONE);
 	node->ioss_ScanDesc->xs_want_itup = true;
 
 	/*
diff --git a/src/backend/executor/nodeIndexscan.c b/src/backend/executor/nodeIndexscan.c
index 3c0b8daf664..1620d146071 100644
--- a/src/backend/executor/nodeIndexscan.c
+++ b/src/backend/executor/nodeIndexscan.c
@@ -114,7 +114,8 @@ IndexNext(IndexScanState *node)
 								   node->iss_Instrument,
 								   node->iss_NumScanKeys,
 								   node->iss_NumOrderByKeys,
-								   SO_NONE);
+								   ScanRelIsReadOnly(&node->ss) ?
+								   SO_HINT_REL_READ_ONLY : SO_NONE);
 
 		node->iss_ScanDesc = scandesc;
 
@@ -211,7 +212,8 @@ IndexNextWithReorder(IndexScanState *node)
 								   node->iss_Instrument,
 								   node->iss_NumScanKeys,
 								   node->iss_NumOrderByKeys,
-								   SO_NONE);
+								   ScanRelIsReadOnly(&node->ss) ?
+								   SO_HINT_REL_READ_ONLY : SO_NONE);
 
 		node->iss_ScanDesc = scandesc;
 
@@ -1733,7 +1735,8 @@ ExecIndexScanInitializeDSM(IndexScanState *node,
 								 node->iss_NumScanKeys,
 								 node->iss_NumOrderByKeys,
 								 piscan,
-								 SO_NONE);
+								 ScanRelIsReadOnly(&node->ss) ?
+								 SO_HINT_REL_READ_ONLY : SO_NONE);
 
 	/*
 	 * If no run-time keys to calculate or they are ready, go ahead and pass
@@ -1798,7 +1801,8 @@ ExecIndexScanInitializeWorker(IndexScanState *node,
 								 node->iss_NumScanKeys,
 								 node->iss_NumOrderByKeys,
 								 piscan,
-								 SO_NONE);
+								 ScanRelIsReadOnly(&node->ss) ?
+								 SO_HINT_REL_READ_ONLY : SO_NONE);
 
 	/*
 	 * 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 cf32df33d82..f3d273e1c5e 100644
--- a/src/backend/executor/nodeSamplescan.c
+++ b/src/backend/executor/nodeSamplescan.c
@@ -299,7 +299,8 @@ tablesample_init(SampleScanState *scanstate)
 									 scanstate->use_bulkread,
 									 allow_sync,
 									 scanstate->use_pagemode,
-									 SO_NONE);
+									 ScanRelIsReadOnly(&scanstate->ss) ?
+									 SO_HINT_REL_READ_ONLY : SO_NONE);
 	}
 	else
 	{
diff --git a/src/backend/executor/nodeSeqscan.c b/src/backend/executor/nodeSeqscan.c
index 09ccc65de1c..04803b0e37d 100644
--- a/src/backend/executor/nodeSeqscan.c
+++ b/src/backend/executor/nodeSeqscan.c
@@ -72,7 +72,8 @@ SeqNext(SeqScanState *node)
 		scandesc = table_beginscan(node->ss.ss_currentRelation,
 								   estate->es_snapshot,
 								   0, NULL,
-								   SO_NONE);
+								   ScanRelIsReadOnly(&node->ss) ?
+								   SO_HINT_REL_READ_ONLY : SO_NONE);
 		node->ss.ss_currentScanDesc = scandesc;
 	}
 
@@ -375,9 +376,11 @@ ExecSeqScanInitializeDSM(SeqScanState *node,
 								  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,
-								 SO_NONE);
+								 ScanRelIsReadOnly(&node->ss) ?
+								 SO_HINT_REL_READ_ONLY : SO_NONE);
 }
 
 /* ----------------------------------------------------------------
@@ -411,5 +414,6 @@ ExecSeqScanInitializeWorker(SeqScanState *node,
 	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,
-								 SO_NONE);
+								 ScanRelIsReadOnly(&node->ss) ?
+								 SO_HINT_REL_READ_ONLY : SO_NONE);
 }
diff --git a/src/backend/executor/nodeTidrangescan.c b/src/backend/executor/nodeTidrangescan.c
index 084e4c6ec90..4a8fe91b2b3 100644
--- a/src/backend/executor/nodeTidrangescan.c
+++ b/src/backend/executor/nodeTidrangescan.c
@@ -246,7 +246,8 @@ TidRangeNext(TidRangeScanState *node)
 												estate->es_snapshot,
 												&node->trss_mintid,
 												&node->trss_maxtid,
-												SO_NONE);
+												ScanRelIsReadOnly(&node->ss) ?
+												SO_HINT_REL_READ_ONLY : SO_NONE);
 			node->ss.ss_currentScanDesc = scandesc;
 		}
 		else
@@ -461,7 +462,9 @@ ExecTidRangeScanInitializeDSM(TidRangeScanState *node, ParallelContext *pcxt)
 	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, SO_NONE);
+										  pscan,
+										  ScanRelIsReadOnly(&node->ss) ?
+										  SO_HINT_REL_READ_ONLY : SO_NONE);
 }
 
 /* ----------------------------------------------------------------
@@ -495,5 +498,7 @@ ExecTidRangeScanInitializeWorker(TidRangeScanState *node,
 	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, SO_NONE);
+										  pscan,
+										  ScanRelIsReadOnly(&node->ss) ?
+										  SO_HINT_REL_READ_ONLY : SO_NONE);
 }
diff --git a/src/include/access/tableam.h b/src/include/access/tableam.h
index 60ceee9decd..5f1c1079cb5 100644
--- a/src/include/access/tableam.h
+++ b/src/include/access/tableam.h
@@ -65,6 +65,9 @@ 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