v11-0001-Fix-BitmapHeapScan-non-parallel-aware-EXPLAIN-AN.patch

From 4a792a3d864761741c7ce5fd0e10a9f1c9539094 Mon Sep 17 00:00:00 2001
From: Melanie Plageman <melanieplageman@gmail.com>
Date: Sun, 5 Apr 2026 16:27:22 -0400
Subject: [PATCH v11 1/2] Fix BitmapHeapScan non-parallel-aware EXPLAIN ANALYZE

Allocate shared bitmap table scan instrumentation in its own DSM chunk,
separate from ParallelBitmapHeapState. Previously, shared
instrumentation was only allocated for parallel-aware nodes, so a
non-parallel-aware bitmap table scan in a parallel query had no shared
instrumentation and EXPLAIN ANALYZE didn't report exact/lossy pages.
This affected queries like bitmap table scans on the outside of a
parallel join or those run with debug_parallel_query=regress. Fix by
allocating a separate DSM chunk for shared instrumentation and doing so
regardless of parallel-awareness.
---
 src/backend/commands/explain.c            |   2 +-
 src/backend/executor/execParallel.c       |   9 ++
 src/backend/executor/nodeBitmapHeapscan.c | 111 +++++++++++++---------
 src/include/executor/nodeBitmapHeapscan.h |   6 ++
 4 files changed, 83 insertions(+), 45 deletions(-)

diff --git a/src/backend/commands/explain.c b/src/backend/commands/explain.c
index 73eaaf176ac..f151f21f9b3 100644
--- a/src/backend/commands/explain.c
+++ b/src/backend/commands/explain.c
@@ -3948,7 +3948,7 @@ show_tidbitmap_info(BitmapHeapScanState *planstate, ExplainState *es)
 	}
 
 	/* Display stats for each parallel worker */
-	if (planstate->pstate != NULL)
+	if (planstate->sinstrument != NULL)
 	{
 		for (int n = 0; n < planstate->sinstrument->num_workers; n++)
 		{
diff --git a/src/backend/executor/execParallel.c b/src/backend/executor/execParallel.c
index 726aca230a4..1a5ec0c305f 100644
--- a/src/backend/executor/execParallel.c
+++ b/src/backend/executor/execParallel.c
@@ -303,6 +303,9 @@ ExecParallelEstimate(PlanState *planstate, ExecParallelEstimateContext *e)
 			if (planstate->plan->parallel_aware)
 				ExecBitmapHeapEstimate((BitmapHeapScanState *) planstate,
 									   e->pcxt);
+			/* even when not parallel-aware, for EXPLAIN ANALYZE */
+			ExecBitmapHeapInstrumentEstimate((BitmapHeapScanState *) planstate,
+											 e->pcxt);
 			break;
 		case T_HashJoinState:
 			if (planstate->plan->parallel_aware)
@@ -542,6 +545,9 @@ ExecParallelInitializeDSM(PlanState *planstate,
 			if (planstate->plan->parallel_aware)
 				ExecBitmapHeapInitializeDSM((BitmapHeapScanState *) planstate,
 											d->pcxt);
+			/* even when not parallel-aware, for EXPLAIN ANALYZE */
+			ExecBitmapHeapInstrumentInitDSM((BitmapHeapScanState *) planstate,
+											d->pcxt);
 			break;
 		case T_HashJoinState:
 			if (planstate->plan->parallel_aware)
@@ -1427,6 +1433,9 @@ ExecParallelInitializeWorker(PlanState *planstate, ParallelWorkerContext *pwcxt)
 			if (planstate->plan->parallel_aware)
 				ExecBitmapHeapInitializeWorker((BitmapHeapScanState *) planstate,
 											   pwcxt);
+			/* even when not parallel-aware, for EXPLAIN ANALYZE */
+			ExecBitmapHeapInstrumentInitWorker((BitmapHeapScanState *) planstate,
+											   pwcxt);
 			break;
 		case T_HashJoinState:
 			if (planstate->plan->parallel_aware)
diff --git a/src/backend/executor/nodeBitmapHeapscan.c b/src/backend/executor/nodeBitmapHeapscan.c
index 73831aed451..d65e2a87b42 100644
--- a/src/backend/executor/nodeBitmapHeapscan.c
+++ b/src/backend/executor/nodeBitmapHeapscan.c
@@ -495,18 +495,8 @@ void
 ExecBitmapHeapEstimate(BitmapHeapScanState *node,
 					   ParallelContext *pcxt)
 {
-	Size		size;
-
-	size = MAXALIGN(sizeof(ParallelBitmapHeapState));
-
-	/* account for instrumentation, if required */
-	if (node->ss.ps.instrument && pcxt->nworkers > 0)
-	{
-		size = add_size(size, offsetof(SharedBitmapHeapInstrumentation, sinstrument));
-		size = add_size(size, mul_size(pcxt->nworkers, sizeof(BitmapHeapScanInstrumentation)));
-	}
-
-	shm_toc_estimate_chunk(&pcxt->estimator, size);
+	shm_toc_estimate_chunk(&pcxt->estimator,
+						   MAXALIGN(sizeof(ParallelBitmapHeapState)));
 	shm_toc_estimate_keys(&pcxt->estimator, 1);
 }
 
@@ -521,27 +511,15 @@ ExecBitmapHeapInitializeDSM(BitmapHeapScanState *node,
 							ParallelContext *pcxt)
 {
 	ParallelBitmapHeapState *pstate;
-	SharedBitmapHeapInstrumentation *sinstrument = NULL;
 	dsa_area   *dsa = node->ss.ps.state->es_query_dsa;
-	char	   *ptr;
-	Size		size;
 
 	/* If there's no DSA, there are no workers; initialize nothing. */
 	if (dsa == NULL)
 		return;
 
-	size = MAXALIGN(sizeof(ParallelBitmapHeapState));
-	if (node->ss.ps.instrument && pcxt->nworkers > 0)
-	{
-		size = add_size(size, offsetof(SharedBitmapHeapInstrumentation, sinstrument));
-		size = add_size(size, mul_size(pcxt->nworkers, sizeof(BitmapHeapScanInstrumentation)));
-	}
-
-	ptr = shm_toc_allocate(pcxt->toc, size);
-	pstate = (ParallelBitmapHeapState *) ptr;
-	ptr += MAXALIGN(sizeof(ParallelBitmapHeapState));
-	if (node->ss.ps.instrument && pcxt->nworkers > 0)
-		sinstrument = (SharedBitmapHeapInstrumentation *) ptr;
+	pstate = (ParallelBitmapHeapState *)
+		shm_toc_allocate(pcxt->toc,
+						 MAXALIGN(sizeof(ParallelBitmapHeapState)));
 
 	pstate->tbmiterator = 0;
 
@@ -551,18 +529,8 @@ ExecBitmapHeapInitializeDSM(BitmapHeapScanState *node,
 
 	ConditionVariableInit(&pstate->cv);
 
-	if (sinstrument)
-	{
-		sinstrument->num_workers = pcxt->nworkers;
-
-		/* ensure any unfilled slots will contain zeroes */
-		memset(sinstrument->sinstrument, 0,
-			   pcxt->nworkers * sizeof(BitmapHeapScanInstrumentation));
-	}
-
 	shm_toc_insert(pcxt->toc, node->ss.ps.plan->plan_node_id, pstate);
 	node->pstate = pstate;
-	node->sinstrument = sinstrument;
 }
 
 /* ----------------------------------------------------------------
@@ -600,17 +568,72 @@ void
 ExecBitmapHeapInitializeWorker(BitmapHeapScanState *node,
 							   ParallelWorkerContext *pwcxt)
 {
-	char	   *ptr;
-
 	Assert(node->ss.ps.state->es_query_dsa != NULL);
 
-	ptr = shm_toc_lookup(pwcxt->toc, node->ss.ps.plan->plan_node_id, false);
+	node->pstate = (ParallelBitmapHeapState *)
+		shm_toc_lookup(pwcxt->toc, node->ss.ps.plan->plan_node_id, false);
+}
+
+/*
+ * Compute the amount of space we'll need for the shared instrumentation and
+ * inform pcxt->estimator.
+ */
+void
+ExecBitmapHeapInstrumentEstimate(BitmapHeapScanState *node,
+								 ParallelContext *pcxt)
+{
+	Size		size;
+
+	if (!node->ss.ps.instrument || pcxt->nworkers == 0)
+		return;
+
+	size = add_size(offsetof(SharedBitmapHeapInstrumentation, sinstrument),
+					mul_size(pcxt->nworkers, sizeof(BitmapHeapScanInstrumentation)));
+	shm_toc_estimate_chunk(&pcxt->estimator, size);
+	shm_toc_estimate_keys(&pcxt->estimator, 1);
+}
+
+/*
+ * Set up parallel bitmap heap scan instrumentation.
+ */
+void
+ExecBitmapHeapInstrumentInitDSM(BitmapHeapScanState *node,
+								ParallelContext *pcxt)
+{
+	Size		size;
+
+	if (!node->ss.ps.instrument || pcxt->nworkers == 0)
+		return;
+
+	size = add_size(offsetof(SharedBitmapHeapInstrumentation, sinstrument),
+					mul_size(pcxt->nworkers, sizeof(BitmapHeapScanInstrumentation)));
+	node->sinstrument =
+		(SharedBitmapHeapInstrumentation *) shm_toc_allocate(pcxt->toc, size);
+
+	/* Each per-worker area must start out as zeroes */
+	memset(node->sinstrument, 0, size);
+	node->sinstrument->num_workers = pcxt->nworkers;
+	shm_toc_insert(pcxt->toc,
+				   node->ss.ps.plan->plan_node_id +
+				   PARALLEL_KEY_SCAN_INSTRUMENT_OFFSET,
+				   node->sinstrument);
+}
 
-	node->pstate = (ParallelBitmapHeapState *) ptr;
-	ptr += MAXALIGN(sizeof(ParallelBitmapHeapState));
+/*
+ * Look up and save the location of the shared instrumentation.
+ */
+void
+ExecBitmapHeapInstrumentInitWorker(BitmapHeapScanState *node,
+								   ParallelWorkerContext *pwcxt)
+{
+	if (!node->ss.ps.instrument)
+		return;
 
-	if (node->ss.ps.instrument)
-		node->sinstrument = (SharedBitmapHeapInstrumentation *) ptr;
+	node->sinstrument = (SharedBitmapHeapInstrumentation *)
+		shm_toc_lookup(pwcxt->toc,
+					   node->ss.ps.plan->plan_node_id +
+					   PARALLEL_KEY_SCAN_INSTRUMENT_OFFSET,
+					   false);
 }
 
 /* ----------------------------------------------------------------
diff --git a/src/include/executor/nodeBitmapHeapscan.h b/src/include/executor/nodeBitmapHeapscan.h
index 5d82f71abff..5c0b6592a1f 100644
--- a/src/include/executor/nodeBitmapHeapscan.h
+++ b/src/include/executor/nodeBitmapHeapscan.h
@@ -28,6 +28,12 @@ extern void ExecBitmapHeapReInitializeDSM(BitmapHeapScanState *node,
 										  ParallelContext *pcxt);
 extern void ExecBitmapHeapInitializeWorker(BitmapHeapScanState *node,
 										   ParallelWorkerContext *pwcxt);
+extern void ExecBitmapHeapInstrumentEstimate(BitmapHeapScanState *node,
+											 ParallelContext *pcxt);
+extern void ExecBitmapHeapInstrumentInitDSM(BitmapHeapScanState *node,
+											ParallelContext *pcxt);
+extern void ExecBitmapHeapInstrumentInitWorker(BitmapHeapScanState *node,
+											   ParallelWorkerContext *pwcxt);
 extern void ExecBitmapHeapRetrieveInstrumentation(BitmapHeapScanState *node);
 
 #endif							/* NODEBITMAPHEAPSCAN_H */
-- 
2.43.0