From: Tom Lane <tgl@sss.pgh.pa.us>
To: Miernik <public@public.miernik.name>
Cc: pgsql-performance@postgresql.org
Subject: Re: why query plan for the inner SELECT of WHERE x IN is wrong, but when run the inner query alone is OK?
Date: Sat, 09 Aug 2008 16:57:58 -0400
Message-ID: <11224.1218315478@sss.pgh.pa.us> (raw)
In-Reply-To: <20080809203435.7227.0.NOFFLE@turbacz.local>
References: <20080809203435.7227.0.NOFFLE@turbacz.local>
Miernik <public@public.miernik.name> writes:
> miernik=> EXPLAIN UPDATE cnts SET p0 = FALSE WHERE uid IN (SELECT uid FROM alog WHERE pid = 3452654 AND o = 1);
> QUERY PLAN
> -----------------------------------------------------------------------------------------------
> Nested Loop IN Join (cost=0.00..3317.34 rows=1 width=44)
> -> Seq Scan on cnts (cost=0.00..36.00 rows=2000 width=44)
> -> Index Scan using alog_uid_idx on alog (cost=0.00..296.95 rows=1 width=4)
> Index Cond: ((alog.uid)::integer = (cnts.uid)::integer)
> Filter: ((alog.pid = 3452654::numeric) AND (alog.o = 1::numeric))
> (5 rows)
> But if I give him only the inner part, it makes reasonable assumptions
> and runs OK:
What's the results for
explain select * from cnts, alog where alog.uid = cnts.uid
?
If necessary, turn off enable_hashjoin and enable_mergejoin so we can
see a comparable plan. I'm suspecting it thinks the condition on
uid is more selective than the one on the other index.
regards, tom lane
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, public@public.miernik.name
Subject: Re: why query plan for the inner SELECT of WHERE x IN is wrong, but when run the inner query alone is OK?
In-Reply-To: <11224.1218315478@sss.pgh.pa.us>
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