From 0b19891ca39f986492d5079dc6406de454bc3511 Mon Sep 17 00:00:00 2001 From: Tomas Vondra Date: Wed, 1 Apr 2026 20:20:57 +0200 Subject: [PATCH v7 4/6] fixup: show prefetch stats for SeqScan --- src/backend/commands/explain.c | 29 +++++---- src/backend/executor/execParallel.c | 16 ++--- src/backend/executor/nodeSeqscan.c | 94 ++++++++++++++++++++--------- 3 files changed, 88 insertions(+), 51 deletions(-) diff --git a/src/backend/commands/explain.c b/src/backend/commands/explain.c index f91e9d0048e..20c5d720516 100644 --- a/src/backend/commands/explain.c +++ b/src/backend/commands/explain.c @@ -4053,21 +4053,26 @@ static void show_scan_io_usage(ScanState *planstate, ExplainState *es) { Plan *plan = planstate->ps.plan; - IOStats stats; + IOStats stats = {0}; if (!es->io) return; - /* scan not started or no prefetch stats */ - if (!(planstate && - planstate->ss_currentScanDesc && - planstate->ss_currentScanDesc->rs_instrument)) - return; - /* - * Initialize counters with stats from the local process first, then - * accumulate data from parallel workers. + * Initialize counters with stats from the local process first. + * + * The scan descriptor may not exist, e.g. if the scan did not start, + * or because of debug_parallel_query=regress. We still want to collect + * data from workers. */ + if (planstate && + planstate->ss_currentScanDesc && + planstate->ss_currentScanDesc->rs_instrument) + { + stats = planstate->ss_currentScanDesc->rs_instrument->io; + } + + /* accumulate data from parallel workers */ switch (nodeTag(plan)) { case T_SeqScan: @@ -4075,9 +4080,6 @@ show_scan_io_usage(ScanState *planstate, ExplainState *es) SharedSeqScanInstrumentation *sinstrument = ((SeqScanState *) planstate)->sinstrument; - /* collect prefetch statistics from the read stream */ - stats = planstate->ss_currentScanDesc->rs_instrument->io; - /* get the sum of the counters set within each and every process */ if (sinstrument) { @@ -4096,9 +4098,6 @@ show_scan_io_usage(ScanState *planstate, ExplainState *es) SharedBitmapHeapInstrumentation *sinstrument = ((BitmapHeapScanState *) planstate)->sinstrument; - /* collect prefetch statistics from the read stream */ - stats = planstate->ss_currentScanDesc->rs_instrument->io; - /* * get the sum of the counters set within each and every * process diff --git a/src/backend/executor/execParallel.c b/src/backend/executor/execParallel.c index d1747993df0..c6f7ee292dd 100644 --- a/src/backend/executor/execParallel.c +++ b/src/backend/executor/execParallel.c @@ -250,9 +250,9 @@ ExecParallelEstimate(PlanState *planstate, ExecParallelEstimateContext *e) switch (nodeTag(planstate)) { case T_SeqScanState: - if (planstate->plan->parallel_aware) - ExecSeqScanEstimate((SeqScanState *) planstate, - e->pcxt); + /* even when not parallel-aware, for EXPLAIN ANALYZE */ + ExecSeqScanEstimate((SeqScanState *) planstate, + e->pcxt); break; case T_IndexScanState: /* even when not parallel-aware, for EXPLAIN ANALYZE */ @@ -484,9 +484,9 @@ ExecParallelInitializeDSM(PlanState *planstate, switch (nodeTag(planstate)) { case T_SeqScanState: - if (planstate->plan->parallel_aware) - ExecSeqScanInitializeDSM((SeqScanState *) planstate, - d->pcxt); + /* even when not parallel-aware, for EXPLAIN ANALYZE */ + ExecSeqScanInitializeDSM((SeqScanState *) planstate, + d->pcxt); break; case T_IndexScanState: /* even when not parallel-aware, for EXPLAIN ANALYZE */ @@ -1366,8 +1366,8 @@ ExecParallelInitializeWorker(PlanState *planstate, ParallelWorkerContext *pwcxt) switch (nodeTag(planstate)) { case T_SeqScanState: - if (planstate->plan->parallel_aware) - ExecSeqScanInitializeWorker((SeqScanState *) planstate, pwcxt); + /* even when not parallel-aware, for EXPLAIN ANALYZE */ + ExecSeqScanInitializeWorker((SeqScanState *) planstate, pwcxt); break; case T_IndexScanState: /* even when not parallel-aware, for EXPLAIN ANALYZE */ diff --git a/src/backend/executor/nodeSeqscan.c b/src/backend/executor/nodeSeqscan.c index 032f3dc5efc..2e4a6138eae 100644 --- a/src/backend/executor/nodeSeqscan.c +++ b/src/backend/executor/nodeSeqscan.c @@ -387,17 +387,25 @@ ExecSeqScanEstimate(SeqScanState *node, ParallelContext *pcxt) { EState *estate = node->ss.ps.state; + bool instrument = node->ss.ps.instrument != NULL; + bool parallel_aware = node->ss.ps.plan->parallel_aware; Size size; + if (!instrument && !parallel_aware) + { + /* No DSM required by the scan */ + return; + } + size = table_parallelscan_estimate(node->ss.ss_currentRelation, - estate->es_snapshot); + estate->es_snapshot); node->pscan_len = size; /* make sure the instrumentation is properly aligned */ size = MAXALIGN(size); /* account for instrumentation, if required */ - if (node->ss.ps.instrument && pcxt->nworkers > 0) + if (instrument && pcxt->nworkers > 0) { size = add_size(size, offsetof(SharedSeqScanInstrumentation, sinstrument)); size = add_size(size, mul_size(pcxt->nworkers, sizeof(SeqScanInstrumentation))); @@ -420,13 +428,20 @@ ExecSeqScanInitializeDSM(SeqScanState *node, EState *estate = node->ss.ps.state; ParallelTableScanDesc pscan; SharedSeqScanInstrumentation *sinstrument = NULL; + bool instrument = node->ss.ps.instrument != NULL; + bool parallel_aware = node->ss.ps.plan->parallel_aware; Size size; - char *ptr; uint32 flags = SO_NONE; + if (!instrument && !parallel_aware) + { + /* No DSM required by the scan */ + return; + } + /* Recalculate the size. This needs to match ExecSeqScanEstimate. */ size = MAXALIGN(node->pscan_len); - if (node->ss.ps.instrument && pcxt->nworkers > 0) + if (instrument && pcxt->nworkers > 0) { size = add_size(size, offsetof(SharedSeqScanInstrumentation, sinstrument)); size = add_size(size, mul_size(pcxt->nworkers, sizeof(SeqScanInstrumentation))); @@ -440,31 +455,38 @@ ExecSeqScanInitializeDSM(SeqScanState *node, estate->es_snapshot); shm_toc_insert(pcxt->toc, node->ss.ps.plan->plan_node_id, pscan); - if (ScanRelIsReadOnly(&node->ss)) - flags |= SO_HINT_REL_READ_ONLY; - - if (estate->es_instrument) - flags |= SO_SCAN_INSTRUMENT; + /* initialize the shared instrumentation (with correct alignment) */ + if (instrument && pcxt->nworkers > 0) + { + char *ptr = (char *) pscan; - node->ss.ss_currentScanDesc = - table_beginscan_parallel(node->ss.ss_currentRelation, pscan, flags); + ptr += MAXALIGN(node->pscan_len); - /* initialize the shared instrumentation (with correct alignment) */ - ptr = (char *) pscan; - ptr += MAXALIGN(node->pscan_len); - if (node->ss.ps.instrument && pcxt->nworkers > 0) sinstrument = (SharedSeqScanInstrumentation *) ptr; - if (sinstrument) - { sinstrument->num_workers = pcxt->nworkers; /* ensure any unfilled slots will contain zeroes */ memset(sinstrument->sinstrument, 0, pcxt->nworkers * sizeof(SeqScanInstrumentation)); + + node->sinstrument = sinstrument; + } + + if (!parallel_aware) + { + /* Only here to set up worker node's shared instrumentation */ + return; } - node->sinstrument = sinstrument; + if (ScanRelIsReadOnly(&node->ss)) + flags |= SO_HINT_REL_READ_ONLY; + + if (estate->es_instrument) + flags |= SO_SCAN_INSTRUMENT; + + node->ss.ss_currentScanDesc = + table_beginscan_parallel(node->ss.ss_currentRelation, pscan, flags); } /* ---------------------------------------------------------------- @@ -493,27 +515,43 @@ void ExecSeqScanInitializeWorker(SeqScanState *node, ParallelWorkerContext *pwcxt) { - EState *estate = node->ss.ps.state; ParallelTableScanDesc pscan; - char *ptr; + EState *estate = node->ss.ps.state; + bool instrument = node->ss.ps.instrument != NULL; + bool parallel_aware = node->ss.ps.plan->parallel_aware; uint32 flags = SO_NONE; + if (!instrument && !parallel_aware) + { + /* No DSM required by the scan */ + return; + } + + pscan = shm_toc_lookup(pwcxt->toc, node->ss.ps.plan->plan_node_id, false); + + /* set pointer to the shared instrumentation */ + if (instrument) + { + char *ptr = (char *) pscan; + ptr += MAXALIGN(pscan->phs_len); + + node->sinstrument = (SharedSeqScanInstrumentation *) ptr; + } + + if (!parallel_aware) + { + /* Only here to set up worker node's SharedInfo */ + return; + } + if (ScanRelIsReadOnly(&node->ss)) flags |= SO_HINT_REL_READ_ONLY; if (estate->es_instrument) flags |= SO_SCAN_INSTRUMENT; - 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, flags); - - /* set pointer to the shared instrumentation */ - ptr = (char *) pscan; - ptr += MAXALIGN(pscan->phs_len); - - if (node->ss.ps.instrument) - node->sinstrument = (SharedSeqScanInstrumentation *) ptr; } /* ---------------------------------------------------------------- -- 2.53.0