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Re: performance problem with LIMIT (order BY in DESC order). Wrong index used?

From:	Claudio Freire <klaussfreire(at)gmail(dot)com>
To:	Dieter Rehbein <dieter(dot)rehbein(at)skiline(dot)cc>
Cc:	pgsql-performance(at)postgresql(dot)org
Subject:	Re: performance problem with LIMIT (order BY in DESC order). Wrong index used?
Date:	2011-04-12 07:42:27
Message-ID:	BANLkTik6U2MU=s9mxr3=pK3Fp+S4bAJK3Q@mail.gmail.com
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On Tue, Apr 12, 2011 at 7:20 AM, Dieter Rehbein
<dieter(dot)rehbein(at)skiline(dot)cc> wrote:
> Hi everybody,
>
> I have a performance-problem with a query using a LIMIT. There are other threads rergading performance issues with LIMIT, but I didn't find useful hints for our problem and it might
> be interesting for other postgres-users.

Did you perform an ANALYZE or VACUUM ANALYZE?
Did you try increasing the statistic targets?

AFAIK, it looks a lot like the planner is missing stats, since it
estimates the index query on idx_nfi_newsfeed will fetch 10k rows -
instead of 25.

In response to

performance problem with LIMIT (order BY in DESC order). Wrong index used? at 2011-04-12 05:20:44 from Dieter Rehbein

Responses

Re: performance problem with LIMIT (order BY in DESC order). Wrong index used? at 2011-04-12 08:59:22 from Dieter Rehbein
Re: performance problem with LIMIT (order BY in DESC order). Wrong index used? at 2011-04-12 14:38:27 from Tom Lane

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