From: Vitalii Tymchyshyn <tivv00@gmail.com>
To: Josh Berkus <josh@agliodbs.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: 8.4/9.0 simple query performance regression
Date: Tue, 07 Jun 2011 11:19:29 +0300
Message-ID: <4DEDDF11.2020801@gmail.com> (raw)
In-Reply-To: <4DED4A87.7000901@agliodbs.com>
References: <4DED4A87.7000901@agliodbs.com>
07.06.11 00:45, Josh Berkus написав(ла):
> All,
>
> Just got this simple case off IRC today:
>
> 8.4.4
> This plan completes in 100ms:
> Filter: (NOT (hashed SubPlan 1))
> 9.0.2
> This plan does not complete in 15 minutes or more:
> Filter: (NOT (SubPlan 1))
"Hashed" is the key. Hashed subplans usually has much better performance.
You need to increase work_mem. I suppose it is in default state as you
need not too much memory for hash of 70K integer values.
BTW: Why do it want to materialize a result of seq scan without filter.
I can see no benefits (or is it more narrow rows?)
Best regards, Vitalii Tymchyshyn
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Subject: Re: 8.4/9.0 simple query performance regression
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