From: | "Scott Marlowe" <smarlowe(at)qwest(dot)net> |
---|---|
To: | "Merlin Moncure" <merlin(dot)moncure(at)rcsonline(dot)com> |
Cc: | "Marius Andreiana" <mandreiana(at)rdslink(dot)ro>, pgsql-performance(at)postgresql(dot)org |
Subject: | Re: NOT IN query takes forever |
Date: | 2004-08-03 18:26:28 |
Message-ID: | 1091557588.27166.94.camel@localhost.localdomain |
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Lists: | pgsql-performance |
On Tue, 2004-08-03 at 10:10, Merlin Moncure wrote:
> > > Try bumping up shared buffers some and sort mem as much as you
> safely
> > > can.
> > Thank you, that did it!
> >
> > With
> > shared_buffers = 3000 # min 16, at least max_connections*2,
> 8KB
> > each
> > sort_mem = 128000 # min 64, size in KB
> >
> > it takes <3 seconds (my hardware is not server-class).
>
> Be careful...sort_mem applies to each connection and (IIRC) in some
> cases more than once to a connection. Of all the configuration
> parameters, sort_mem (IMO) is the most important and the hardest to get
> right. 128k (or 128MB) is awfully high unless you have a ton of memory
> (you don't) or you are running in single connection scenarios. Do some
> experimentation by lowering the value until you get a good balance
> between potential memory consumption and speed.
Minor nit, sort_mem actually applies to EACH sort individually, so a
query that had to run three sorts could use 3 x sort_mem.
Note that one can set sort_mem per backend connection with set
sort_mem=128000 if need be so as not to use up all the memory with other
backends.
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