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Re: Recommendations for set statistics

From: Josh Berkus <josh(at)agliodbs(dot)com>
To: Christopher Browne <cbbrowne(at)acm(dot)org>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: Recommendations for set statistics
Date: 2005-05-13 16:22:11
Message-ID: 200505130922.11582.josh@agliodbs.com (view raw or flat)
Thread:
Lists: pgsql-performance
Chris,

> It is widely believed that a somewhat larger default than 10 would be
> a "good thing," as it seems to be fairly common for 10 to be too small
> to allow statistics to be stable.  But nobody has done any formal
> evaluation as to whether it would make sense to jump from 10 to:
>
>  - 15?
>  - 20?
>  - 50?
>  - 100?
>  - More than that?

My anecdotal experience is that if more than 10 is required, you generally 
need to jump to at least 100, and more often 250.   On the other end, I've 
generally not found any difference between 400 and 1000 when it comes to 
"bad" queries.

I have an unfinished patch in the works which goes through and increases the 
stats_target for all *indexed* columns to 100 or so.   However, I've needed 
to work up a test case to prove the utility of it.

-- 
Josh Berkus
Aglio Database Solutions
San Francisco

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