From 95babe8447eadb40c2d1452a9102d4766269d80f Mon Sep 17 00:00:00 2001 From: James Coleman Date: Sun, 15 Mar 2020 20:27:19 -0400 Subject: [PATCH v3] Show bitmap only unfetched page count to EXPLAIN 7c70996ebf0949b142a99 added an optimization to bitmap heap scans to avoid fetching the heap page where the visibility map makes that possible, much like index only scans. However that commit didn't add this output to EXPLAIN, so it's not obvious when the optimization is kicking in and when it's not. So, track the number of skipped pages and report it in EXPLAIN output. Author: Jeff Janes Reviewers: Emre Hasegeli, Alexey Bashtanov, James Coleman --- src/backend/commands/explain.c | 8 +++++++- src/backend/executor/nodeBitmapHeapscan.c | 5 +++-- src/include/nodes/execnodes.h | 2 ++ 3 files changed, 12 insertions(+), 3 deletions(-) diff --git a/src/backend/commands/explain.c b/src/backend/commands/explain.c index d901dc4a50..5a5e04ecbb 100644 --- a/src/backend/commands/explain.c +++ b/src/backend/commands/explain.c @@ -2777,6 +2777,8 @@ show_tidbitmap_info(BitmapHeapScanState *planstate, ExplainState *es) { if (es->format != EXPLAIN_FORMAT_TEXT) { + ExplainPropertyInteger("Unfetched Heap Blocks", NULL, + planstate->unfetched_pages, es); ExplainPropertyInteger("Exact Heap Blocks", NULL, planstate->exact_pages, es); ExplainPropertyInteger("Lossy Heap Blocks", NULL, @@ -2784,10 +2786,14 @@ show_tidbitmap_info(BitmapHeapScanState *planstate, ExplainState *es) } else { - if (planstate->exact_pages > 0 || planstate->lossy_pages > 0) + if (planstate->exact_pages > 0 || planstate->lossy_pages > 0 + || planstate->unfetched_pages > 0) { ExplainIndentText(es); appendStringInfoString(es->str, "Heap Blocks:"); + if (planstate->unfetched_pages > 0) + appendStringInfo(es->str, " unfetched=%ld", + planstate->unfetched_pages); if (planstate->exact_pages > 0) appendStringInfo(es->str, " exact=%ld", planstate->exact_pages); if (planstate->lossy_pages > 0) diff --git a/src/backend/executor/nodeBitmapHeapscan.c b/src/backend/executor/nodeBitmapHeapscan.c index ae8a11da30..dce955636f 100644 --- a/src/backend/executor/nodeBitmapHeapscan.c +++ b/src/backend/executor/nodeBitmapHeapscan.c @@ -231,14 +231,14 @@ BitmapHeapNext(BitmapHeapScanState *node) * node->return_empty_tuples. */ node->return_empty_tuples = tbmres->ntuples; + node->unfetched_pages++; } else if (!table_scan_bitmap_next_block(scan, tbmres)) { /* AM doesn't think this block is valid, skip */ continue; } - - if (tbmres->ntuples >= 0) + else if (tbmres->ntuples >= 0) node->exact_pages++; else node->lossy_pages++; @@ -734,6 +734,7 @@ ExecInitBitmapHeapScan(BitmapHeapScan *node, EState *estate, int eflags) scanstate->pvmbuffer = InvalidBuffer; scanstate->exact_pages = 0; scanstate->lossy_pages = 0; + scanstate->unfetched_pages = 0; scanstate->prefetch_iterator = NULL; scanstate->prefetch_pages = 0; scanstate->prefetch_target = 0; diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h index cd3ddf781f..32400be08c 100644 --- a/src/include/nodes/execnodes.h +++ b/src/include/nodes/execnodes.h @@ -1567,6 +1567,7 @@ typedef struct ParallelBitmapHeapState * pvmbuffer ditto, for prefetched pages * exact_pages total number of exact pages retrieved * lossy_pages total number of lossy pages retrieved + * unfetched_pages total number of pages not retrieved due to vm * prefetch_iterator iterator for prefetching ahead of current page * prefetch_pages # pages prefetch iterator is ahead of current * prefetch_target current target prefetch distance @@ -1591,6 +1592,7 @@ typedef struct BitmapHeapScanState Buffer pvmbuffer; long exact_pages; long lossy_pages; + long unfetched_pages; TBMIterator *prefetch_iterator; int prefetch_pages; int prefetch_target; -- 2.17.1