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Fix EXPLAIN Bitmap heap scan to count pages with no visible tuples 

Previously, bitmap heap scans only counted lossy and exact pages for
explain when there was at least one visible tuple on the page.

heapam_scan_bitmap_next_block() returned true only if there was a
"valid" page with tuples to be processed. However, the lossy and exact
page counters in EXPLAIN should count the number of pages represented
in a lossy or non-lossy way in the constructed bitmap, regardless of
whether or not the pages ultimately contained visible tuples.

Backpatch to all supported versions.

Author: Melanie Plageman
Discussion: https://www.postgresql.org/message-id/CAAKRu_ZwCwWFeL_H3ia26bP2e7HiKLWt0ZmGXPVwPO6uXq0vaA@mail.gmail.com
Discussion: https://www.postgresql.org/message-id/CAAKRu_bxrXeZ2rCnY8LyeC2Ls88KpjWrQ%2BopUrXDRXdcfwFZGA@mail.gmail.com
This commit is contained in:
Heikki Linnakangas 2024-03-18 14:04:28 +02:00
parent 82c87af7a0
commit f3e4581acd
2 changed files with 9 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
src/backend/executor/nodeBitmapHeapscan.c
View File

@ -208,6 +208,11 @@ BitmapHeapNext(BitmapHeapScanState *node)
BitmapAdjustPrefetchIterator(node, tbmres);
if (tbmres->ntuples >= 0)
node->exact_pages++;
else
node->lossy_pages++;
/*
* We can skip fetching the heap page if we don't need any fields
* from the heap, and the bitmap entries don't need rechecking,
@ -239,11 +244,6 @@ BitmapHeapNext(BitmapHeapScanState *node)
continue;
}
if (tbmres->ntuples >= 0)
node->exact_pages++;
else
node->lossy_pages++;
/* Adjust the prefetch target */
BitmapAdjustPrefetchTarget(node);
}

5
src/test/regress/expected/partition_prune.out
View File

@ -2964,6 +2964,7 @@ update ab_a1 set b = 3 from ab where ab.a = 1 and ab.a = ab_a1.a;
Index Cond: (a = 1)
-> Bitmap Heap Scan on ab_a1_b3 ab_a1_b3_1 (actual rows=0 loops=1)
Recheck Cond: (a = 1)
Heap Blocks: exact=1
-> Bitmap Index Scan on ab_a1_b3_a_idx (actual rows=1 loops=1)
Index Cond: (a = 1)
-> Materialize (actual rows=1 loops=1)
@ -2985,14 +2986,16 @@ update ab_a1 set b = 3 from ab where ab.a = 1 and ab.a = ab_a1.a;
Index Cond: (a = 1)
-> Bitmap Heap Scan on ab_a1_b3 ab_a1_b3_1 (actual rows=0 loops=1)
Recheck Cond: (a = 1)
Heap Blocks: exact=1
-> Bitmap Index Scan on ab_a1_b3_a_idx (actual rows=1 loops=1)
Index Cond: (a = 1)
-> Materialize (actual rows=0 loops=1)
-> Bitmap Heap Scan on ab_a1_b3 (actual rows=0 loops=1)
Recheck Cond: (a = 1)
Heap Blocks: exact=1
-> Bitmap Index Scan on ab_a1_b3_a_idx (actual rows=1 loops=1)
Index Cond: (a = 1)
(65 rows)
(68 rows)
table ab;
a | b