From: | Ed Tyrrill <tyrrill_ed(at)emc(dot)com> |
---|---|
To: | Stephen Frost <sfrost(at)snowman(dot)net> |
Cc: | pgsql-performance(at)postgresql(dot)org |
Subject: | Re: |
Date: | 2007-06-25 23:39:02 |
Message-ID: | 1182814742.6477.5.camel@nickel.avamar.com |
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Thread: | |
Lists: | pgsql-performance |
On Mon, 2007-06-25 at 17:56 -0400, Stephen Frost wrote:
> Was the 'work_mem' set to the same thing on all these runs? Also, you
> might try increasing the 'work_mem' under 8.2.4, at least for this query
> (you can set it by just doing: set work_mem = '2GB'; or similar in psql,
> or you can change the default in postgresql.conf).
>
> The big thing of note, it seems, is that you've got enough memory and
> it's coming out faster when doing a hash-join vs. a sort + merge-join.
> Could likely be because it doesn't think there's enough work memory
> available for the hash, which might change based on the values it gets
> from the statistics on how frequently something shows up, etc.
>
> Enjoy,
>
> Stephen
Yes, work_mem was set to 128MB for all runs. All settings were the same
except for the change to default_statistics_target. I'm certainly
memory constrained, but giving 2GB to one one session doesn't allow
other sessions to do anything. Possibly when we upgrade to 16GB. :-)
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