Show Parallel Bitmap Heap Scan worker stats in EXPLAIN ANALYZE

Nodes like Memoize report the cache stats for each parallel worker, so it
makes sense to show the exact and lossy pages in Parallel Bitmap Heap Scan
in a similar way.  Likewise, Sort shows the method and memory used for
each worker.

There was some discussion on whether the leader stats should include the
totals for each parallel worker or not.  I did some analysis on this to
see what other parallel node types do and it seems only Parallel Hash does
anything like this.  All the rest, per what's supported by
ExecParallelRetrieveInstrumentation() are consistent with each other.

Author: David Geier <geidav.pg@gmail.com>
Author: Heikki Linnakangas <hlinnaka@iki.fi>
Author: Donghang Lin <donghanglin@gmail.com>
Author: Alena Rybakina <lena.ribackina@yandex.ru>
Author: David Rowley <dgrowleyml@gmail.com>
Reviewed-by: Dmitry Dolgov <9erthalion6@gmail.com>
Reviewed-by: Michael Christofides <michael@pgmustard.com>
Reviewed-by: Robert Haas <robertmhaas@gmail.com>
Reviewed-by: Dilip Kumar <dilipbalaut@gmail.com>
Reviewed-by: Tomas Vondra <tomas.vondra@enterprisedb.com>
Reviewed-by: Melanie Plageman <melanieplageman@gmail.com>
Reviewed-by: Donghang Lin <donghanglin@gmail.com>
Reviewed-by: Masahiro Ikeda <Masahiro.Ikeda@nttdata.com>
Discussion: https://postgr.es/m/b3d80961-c2e5-38cc-6a32-61886cdf766d%40gmail.com

1 files changed, 96 insertions, 9 deletions

diff --git a/src/backend/executor/nodeBitmapHeapscan.c b/src/backend/executor/nodeBitmapHeapscan.c
index 6b48a6d8350..3c63bdd93df 100644
--- a/src/backend/executor/nodeBitmapHeapscan.c
+++ b/src/backend/executor/nodeBitmapHeapscan.c
@@ -236,9 +236,9 @@ BitmapHeapNext(BitmapHeapScanState *node)
 			valid_block = table_scan_bitmap_next_block(scan, tbmres);
 
 			if (tbmres->ntuples >= 0)
-				node->exact_pages++;
+				node->stats.exact_pages++;
 			else
-				node->lossy_pages++;
+				node->stats.lossy_pages++;
 
 			if (!valid_block)
 			{
@@ -628,6 +628,29 @@ ExecEndBitmapHeapScan(BitmapHeapScanState *node)
 	TableScanDesc scanDesc;
 
 	/*
+	 * When ending a parallel worker, copy the statistics gathered by the
+	 * worker back into shared memory so that it can be picked up by the main
+	 * process to report in EXPLAIN ANALYZE.
+	 */
+	if (node->sinstrument != NULL && IsParallelWorker())
+	{
+		BitmapHeapScanInstrumentation *si;
+
+		Assert(ParallelWorkerNumber <= node->sinstrument->num_workers);
+		si = &node->sinstrument->sinstrument[ParallelWorkerNumber];
+
+		/*
+		 * Here we accumulate the stats rather than performing memcpy on
+		 * node->stats into si.  When a Gather/GatherMerge node finishes it
+		 * will perform planner shutdown on the workers.  On rescan it will
+		 * spin up new workers which will have a new BitmapHeapScanState and
+		 * zeroed stats.
+		 */
+		si->exact_pages += node->stats.exact_pages;
+		si->lossy_pages += node->stats.lossy_pages;
+	}
+
+	/*
 	 * extract information from the node
 	 */
 	scanDesc = node->ss.ss_currentScanDesc;
@@ -694,8 +717,10 @@ ExecInitBitmapHeapScan(BitmapHeapScan *node, EState *estate, int eflags)
 	scanstate->tbmiterator = NULL;
 	scanstate->tbmres = NULL;
 	scanstate->pvmbuffer = InvalidBuffer;
-	scanstate->exact_pages = 0;
-	scanstate->lossy_pages = 0;
+
+	/* Zero the statistics counters */
+	memset(&scanstate->stats, 0, sizeof(BitmapHeapScanInstrumentation));
+
 	scanstate->prefetch_iterator = NULL;
 	scanstate->prefetch_pages = 0;
 	scanstate->prefetch_target = 0;
@@ -803,7 +828,18 @@ void
 ExecBitmapHeapEstimate(BitmapHeapScanState *node,
 					   ParallelContext *pcxt)
 {
-	shm_toc_estimate_chunk(&pcxt->estimator, sizeof(ParallelBitmapHeapState));
+	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_keys(&pcxt->estimator, 1);
 }
 
@@ -818,13 +854,27 @@ 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;
 
-	pstate = shm_toc_allocate(pcxt->toc, sizeof(ParallelBitmapHeapState));
+	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->tbmiterator = 0;
 	pstate->prefetch_iterator = 0;
@@ -837,8 +887,18 @@ 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;
 }
 
 /* ----------------------------------------------------------------
@@ -880,10 +940,37 @@ void
 ExecBitmapHeapInitializeWorker(BitmapHeapScanState *node,
 							   ParallelWorkerContext *pwcxt)
 {
-	ParallelBitmapHeapState *pstate;
+	char	   *ptr;
 
 	Assert(node->ss.ps.state->es_query_dsa != NULL);
 
-	pstate = shm_toc_lookup(pwcxt->toc, node->ss.ps.plan->plan_node_id, false);
-	node->pstate = pstate;
+	ptr = shm_toc_lookup(pwcxt->toc, node->ss.ps.plan->plan_node_id, false);
+
+	node->pstate = (ParallelBitmapHeapState *) ptr;
+	ptr += MAXALIGN(sizeof(ParallelBitmapHeapState));
+
+	if (node->ss.ps.instrument)
+		node->sinstrument = (SharedBitmapHeapInstrumentation *) ptr;
+}
+
+/* ----------------------------------------------------------------
+ *		ExecBitmapHeapRetrieveInstrumentation
+ *
+ *		Transfer bitmap heap scan statistics from DSM to private memory.
+ * ----------------------------------------------------------------
+ */
+void
+ExecBitmapHeapRetrieveInstrumentation(BitmapHeapScanState *node)
+{
+	SharedBitmapHeapInstrumentation *sinstrument = node->sinstrument;
+	Size		size;
+
+	if (sinstrument == NULL)
+		return;
+
+	size = offsetof(SharedBitmapHeapInstrumentation, sinstrument)
+		+ sinstrument->num_workers * sizeof(BitmapHeapScanInstrumentation);
+
+	node->sinstrument = palloc(size);
+	memcpy(node->sinstrument, sinstrument, size);
 }