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

diff --git a/src/backend/executor/nodeBitmapHeapscan.c b/src/backend/executor/nodeBitmapHeapscan.c
index f62105f5284007ed2af0fb36c9feb0289b098a69..15abed130414d5034c488dad8109b6cb00f410f5 100644 (file)
--- a/src/backend/executor/nodeBitmapHeapscan.c
+++ b/src/backend/executor/nodeBitmapHeapscan.c
@@ -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);
        }

diff --git a/src/test/regress/expected/partition_prune.out b/src/test/regress/expected/partition_prune.out
index 7fde46113ea87f48d4a150c9820923ee0bb749f3..d5b009077bbc98b33304b08d9479b3dec3c2ee2b 100644 (file)
--- a/src/test/regress/expected/partition_prune.out
+++ b/src/test/regress/expected/partition_prune.out
@@ -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