From: Ilia Kantor <ilia@obnovlenie.ru>
To: pgsql-performance@postgresql.org
Subject: Bitmap scan when it is not needed
Date: Mon, 29 Aug 2005 00:48:40 +0400
Message-ID: <auto-000558491990@umail.ru> (raw)
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..
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To: pgsql-performance@postgresql.org
Cc: ilia@obnovlenie.ru
Subject: Re: Bitmap scan when it is not needed
In-Reply-To: <auto-000558491990@umail.ru>
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