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Re: Very high effective_cache_size == worse performance?

From: David Kerr <dmk(at)mr-paradox(dot)net>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: Very high effective_cache_size == worse performance?
Date: 2010-04-20 18:47:27
Message-ID: 20100420184727.GE53489@mr-paradox.net (view raw or flat)
Thread:
Lists: pgsql-performance
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 did turn on log_min_duration_statement but that caused performance to be unbearable,
- > but i could turn it on again if it would help.
- 
- I think you need to find a way to identify exactly which query is
- running slowly.  You could sit there and run "select * from
- pg_stat_activity", or turn on log_min_duration_statement, or have your
- application print out timestamps at key points, or some other
- method...

I'm on it.

Dave

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