Обсуждение: EXPLAIN ANALYZE for bitmapAnd and bitmapOr scans always reports rows = 0

From this snipped you can see that the Bitmap Heap scan returns 123
rows, but the BitmapAnd under it returns 0.  I would find it useful to
determine how many rows were thrown out by the recheck.

                      ->  Bitmap Heap Scan on d  (cost=4959.18..16848.23
rows=754 width=10) (actual time=344.126..1534.198 rows=123 loops=1)
                            Recheck Cond: ((s = $0) AND (sdate >=
'2007-06-30'::date) AND (sdate <= '2007-07-30'::date))
                            Filter: (snipped filter conditions here)
                            ->  BitmapAnd  (cost=4959.18..4959.18
rows=3218 width=0) (actual time=337.002..337.002 rows=0 loops=1)
                                  ->  Bitmap Index Scan on d_idx1
(cost=0.00..1035.58 rows=54796 width=0) (actual time=96.478..96.478
rows=30338 loops=1)
                                        Index Cond: (s = $0)
                                  ->  Bitmap Index Scan on d_idx2
(cost=0.00..3922.98 rows=183437 width=0) (actual time=235.680..235.680
rows=181322 loops=1)
                                        Index Cond: ((sdate >=
'2007-06-30'::date) AND (sdate <= '2007-07-30'::date))

This was on:
PostgreSQL 8.2.4 on x86_64-unknown-linux-gnu, compiled by GCC gcc (GCC)
3.4.6 20060404 (Red Hat 3.4.6-3)

Joseph S wrote:
> From this snipped you can see that the Bitmap Heap scan returns 123
> rows, but the BitmapAnd under it returns 0.  I would find it useful to
> determine how many rows were thrown out by the recheck.

Yeah, it would be nice. Unfortunately there's some problems with that,
see previous discussion on that:
http://archives.postgresql.org/pgsql-bugs/2007-04/msg00029.php

--
  Heikki Linnakangas
  EnterpriseDB   http://www.enterprisedb.com