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Re: [PATCHES] Better default_statistics_target

From: Gregory Stark <stark(at)enterprisedb(dot)com>
To: "Decibel!" <decibel(at)decibel(dot)org>
Cc: "Christopher Browne" <cbbrowne(at)gmail(dot)com>, "Guillaume Smet" <guillaume(dot)smet(at)gmail(dot)com>, "Greg Sabino Mullane" <greg(at)turnstep(dot)com>, <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [PATCHES] Better default_statistics_target
Date: 2008-01-30 23:08:45
Message-ID: 873asevrlu.fsf@oxford.xeocode.com (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-patches
"Decibel!" <decibel(at)decibel(dot)org> writes:

> I think that before doing any of that you'd be much better off
> investigating how much performance penalty there is for maxing out
> default_statistict_target. If, as I suspect, it's essentially 0 on
> modern hardware, then I don't think it's worth any more effort.

That's not my experience. Even just raising it to 100 multiplies the number of
rows ANALYZE has to read by 10. And the arrays for every column become ten
times larger. Eventually they start being toasted...

> BTW, that investigation wouldn't just be academic either; if we could
> convince ourselves that there normally wasn't any cost associated with a
> high default_statistics_target, we could increase the default, which
> would reduce the amount of traffic we'd see on -performance about bad
> query plans.

I suspect we could raise it, we just don't know by how much.

-- 
  Gregory Stark
  EnterpriseDB          http://www.enterprisedb.com
  Ask me about EnterpriseDB's 24x7 Postgres support!

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