pg.ddx.io pgsql-performance@postgresql.org mailing list archive
help / color / mirror / Atom feedBitmap scan when it is not needed
2+ messages / 2 participants
[nested] [flat]
* Bitmap scan when it is not needed
@ 2005-08-28 20:48 Ilia Kantor <ilia@obnovlenie.ru>
2005-08-28 22:49 ` Re: Bitmap scan when it is not needed Tom Lane <tgl@sss.pgh.pa.us>
0 siblings, 1 reply; 2+ messages in thread
From: Ilia Kantor @ 2005-08-28 20:48 UTC (permalink / raw)
To: pgsql-performance
explain analyze select * from objects_hier where tg && array[0] and id
<10000;
Bitmap Heap Scan on objects_hier (cost=4.79..8.80 rows=1 width=337) (actual
time=0.110..0.110 rows=0 loops=1)
Recheck Cond: ((tg && '{0}'::integer[]) AND (id < 10000))
-> BitmapAnd (cost=4.79..4.79 rows=1 width=0) (actual time=0.106..0.106
rows=0 loops=1)
-> Bitmap Index Scan on gistbla2 (cost=0.00..2.10 rows=30
width=0) (actual time=0.042..0.042 rows=0 loops=1)
Index Cond: (tg && '{0}'::integer[])
-> Bitmap Index Scan on ohid (cost=0.00..2.44 rows=1240 width=0)
(actual time=0.058..0.058 rows=1255 loops=1)
Index Cond: (id < 10000)
I see, Bitmap is going to AND my indexes.. It read one with less number of
rows estimated the first (right)..
It found 0 records at gistbla2 index.
Then why is it reading ohid ?
Maybe a quickfix is possible for cases when 0 records is found to stop
reading other AND elements..
^ permalink raw reply [nested|flat] 2+ messages in thread
* Re: Bitmap scan when it is not needed
2005-08-28 20:48 Bitmap scan when it is not needed Ilia Kantor <ilia@obnovlenie.ru>
@ 2005-08-28 22:49 ` Tom Lane <tgl@sss.pgh.pa.us>
0 siblings, 0 replies; 2+ messages in thread
From: Tom Lane @ 2005-08-28 22:49 UTC (permalink / raw)
To: Ilia Kantor <ilia@obnovlenie.ru>; +Cc: pgsql-performance
"Ilia Kantor" <ilia@obnovlenie.ru> writes:
> Maybe a quickfix is possible for cases when 0 records is found to stop
> reading other AND elements..
Not sure how useful this will be in practice (since the planner tends
not to bother ANDing unselective indexes at all), but it's easy enough
to do ... so I did it.
regards, tom lane
^ permalink raw reply [nested|flat] 2+ messages in thread
end of thread, other threads:[~2005-08-28 22:49 UTC | newest]
Thread overview: 2+ messages (download: mbox mbox.gz follow: Atom feed)
-- links below jump to the message on this page --
2005-08-28 20:48 Bitmap scan when it is not needed Ilia Kantor <ilia@obnovlenie.ru>
2005-08-28 22:49 ` Tom Lane <tgl@sss.pgh.pa.us>
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox