From: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
---|---|
To: | Mark Wong <markwkm(at)gmail(dot)com> |
Cc: | "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org>, Selena Deckelmann <selenamarie(at)gmail(dot)com>, Gabrielle Roth <gorthx(at)gmail(dot)com> |
Subject: | Re: dbt-2 tuning results with postgresql-8.3.5 |
Date: | 2008-12-24 14:14:06 |
Message-ID: | 1230128046.4793.1145.camel@ebony.2ndQuadrant |
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Thread: | |
Lists: | pgsql-performance |
Hi Mark,
Good to see you producing results again.
On Sat, 2008-12-20 at 16:54 -0800, Mark Wong wrote:
> Here are links to how the throughput changes when increasing shared_buffers:
>
> http://pugs.postgresql.org/node/505
Only starnge thing here is the result at 22528MB. It's the only normal
one there. Seems to be a freeze occurring on most tests around the 30
minute mark, which delays many backends and reduces writes.
Reduction in performance as shared_buffers increases looks normal.
Increase wal_buffers, but look for something else as well. Try to get a
backtrace from when the lock up happens. It may not be Postgres?
> And another series of tests to show how throughput changes when
> checkpoint_segments are increased:
>
> http://pugs.postgresql.org/node/503
>
> The links go to a graphical summary and raw data. Note that the
> maximum theoretical throughput at this scale factor is approximately
> 12000 notpm.
>
> My first glance takes tells me that the system performance is quite
> erratic when increasing the shared_buffers. I'm also not what to
> gather from increasing the checkpoint_segments. Is it simply that the
> more checkpoint segments you have, the more time the database spends
> fsyncing when at a checkpoint?
I would ignore the checkpoint_segment tests because you aren't using a
realistic value of shared_buffers. I doubt any such effect is noticeable
when you use a realistic value determined from set of tests 505.
--
Simon Riggs www.2ndQuadrant.com
PostgreSQL Training, Services and Support
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