On Mon, Dec 22, 2008 at 12:59 AM, Greg Smith <gsmith(at)gregsmith(dot)com> wrote:
> On Sat, 20 Dec 2008, Mark Wong wrote:
>> Here are links to how the throughput changes when increasing
>> shared_buffers: http://pugs.postgresql.org/node/505 My first glance takes
>> tells me that the system performance is quite erratic when increasing the
> If you smooth that curve out a bit, you have to throw out the 22528MB figure
> as meaningless--particularly since it's way too close to the cliff where
> performance dives hard. The sweet spot looks to me like 11264MB to 17408MB.
> I'd say 14336MB is the best performing setting that's in the middle of a
> stable area.
>> And another series of tests to show how throughput changes when
>> checkpoint_segments are increased: http://pugs.postgresql.org/node/503 I'm
>> also not what to gather from increasing the checkpoint_segments.
> What was shared_buffers set to here? Those two settings are not completely
> independent, for example at a tiny buffer size it's not as obvious there's a
> win in spreading the checkpoints out more. It's actually a 3-D graph, with
> shared_buffers and checkpoint_segments as two axes and the throughput as the
> Z value.
> Since that's quite time consuming to map out in its entirety, the way I'd
> suggest navigating the territory more efficiently is to ignore the defaults
> altogether. Start with a configuration that someone familiar with tuning
> the database would pick for this hardware: 8192MB for shared_buffers and
> 100 checkpoint segments would be a reasonable base point. Run the same
> tests you did here, but with the value you're not changing set to those much
> larger values rather than the database defaults, and then I think you'd end
> with something more interesting. Also, I think the checkpoint_segments
> values >500 are a bit much, given what level of recovery time would come
> with a crash at that setting. Smaller steps from a smaller range would be
> better there I think.
Sorry for the long delay. I have a trio of results (that I actually
ran about four weeks ago) setting the shared_buffers to 7680MB (I
don't know remember why it wasn't set to 8192MB :( ) and
checkpoint_segments to 100:
I'm also capturing the PostgreSQL parameters as suggested so we can
see what's set in the config file, default, command line etc. It's
the "Settings" link in the "System Summary" section on the report web
So about a 7% change for this particular workload:
We're re-running some filesystem tests for an upcoming conference, so
we'll get back to it shortly...
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