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Date: Tue, 12 Apr 2011 11:33:31 +0200
Subject: Re: performance problem with LIMIT (order BY in DESC
	order). Wrong index used?
From: tv@fuzzy.cz
To: "Claudio Freire" <klaussfreire@gmail.com>
Cc: "Dieter Rehbein" <dieter.rehbein@skiline.cc>,
	pgsql-performance@postgresql.org
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> On Tue, Apr 12, 2011 at 10:59 AM, Dieter Rehbein
> <dieter.rehbein@skiline.cc> wrote:
>> I just executed a VACUUM ANALYZE and now everything performs well. hm,
>> strange.
>
> That probably means you need more statistics - try increasing the
> newsfeed's statistics target count.
>
> ALTER TABLE newsfeed_item ALTER COLUMN newsfeed SET STATISTICS <n>;
>
> Try different <n> numbers, you can crank it up to 4000 or perhaps more
> in 9.0, but you should start lower I guess.

AFAIK the max value is 10000 and the default is 100. Higher numbers mean
higher overhead, so do not jump to 10000 directly. Set it to 1000 and see
if that helps, etc.

regards
Tomas