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Re: PG 8.3 and large shared buffer settings

From: Dan Sugalski <dan(at)sidhe(dot)org>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: PG 8.3 and large shared buffer settings
Date: 2009-09-25 10:05:38
Message-ID: a06240803c6e23fd57b77@[172.16.5.2] (view raw, whole thread or download thread mbox)
Thread:
Lists: pgsql-performance
At 12:36 AM -0400 9/25/09, Tom Lane wrote:
>Dan Sugalski <dan(at)sidhe(dot)org> writes:
>>  Is there any practical limit to the number of shared buffers PG 8.3.7
>>  can handle before more becomes counter-productive?
>
>Probably, but I've not heard any definitive measurements showing an
>upper limit.  The traditional wisdom of limiting it to 1G or so dates
>from before the last rounds of revisions to the bufmgr logic.

Excellent.

>  > My production DB's around 200G, and the box hosting it has 192G of
>>  memory on it, running a 64 bit AIX build of 8.3.7.
>
>Yowza.  You might be able to do measurements that no one has done
>before.  Let us know what you find out.

:) It's a machine of non-trivial size, to be sure. I'll give the 
buffer setting a good bump and see how it goes. I may be able to take 
one of the slony replicas off-line the next holiday and run some 
performance tests, but that won't be for a while.

>BTW, does AIX have any provision for locking shared memory into RAM?
>One of the gotchas for large shared memory has always been the risk
>that the kernel would decide to swap some of it out.

I'll have to go check, but I think it does. This box hasn't actually 
hit swap since it started --  a good chunk of that RAM is used as 
semi-permanent disk cache but unfortunately the regular day-to-day 
use of this box (they won't let me have it as a dedicated DB-only 
machine. Go figure :) doing other stuff the cache tends to turn over 
pretty quickly.
-- 
				Dan

--------------------------------------it's like this-------------------
Dan Sugalski                          even samurai
dan(at)sidhe(dot)org                         have teddy bears and even
                                       teddy bears get drunk

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