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Re: Very high effective_cache_size == worse performance?

From: Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>
To: David Kerr <dmk(at)mr-paradox(dot)net>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Very high effective_cache_size == worse performance?
Date: 2010-04-20 19:22:36
Message-ID: q2udcc563d11004201222se02e858fv50b78b96b9d2c015@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
On Tue, Apr 20, 2010 at 12:47 PM, David Kerr <dmk(at)mr-paradox(dot)net> wrote:
> On Tue, Apr 20, 2010 at 02:15:19PM -0400, Robert Haas wrote:
> - On Tue, Apr 20, 2010 at 2:03 PM, David Kerr <dmk(at)mr-paradox(dot)net> wrote:
> - > that thought occured to me while I was testing this. I ran a vacuumdb -z
> - > on my database during the load and it didn't impact performance at all.
> -
> - The window to run ANALYZE usefully is pretty short.  If you run it
> - before the load is complete, your stats will be wrong.  If you run it
> - after the select statements that hit the table are planned, the
> - updated stats won't arrive in time to do any good.
>
> right, but i'm loading 20 million records in 1000 record increments. so
> the analyze should affect all subsequent increments, no?

I keep thinking FK checks are taking a long time because they aren't
cached because in import they went through the ring buffer in pg or
some other way aren't in a buffer but large effective cache size says
it's 99.99% chance or better that it's in cache, and chooses a poor
plan to look them up.  Just a guess.

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Subject: Re: Very high effective_cache_size == worse performance?
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