From: Gregory Stark <stark@enterprisedb.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Gaetano Mendola <mendola@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: shared_buffers performance
Date: Mon, 14 Apr 2008 20:58:21 +0100
Message-ID: <874pa4gqea.fsf@oxford.xeocode.com> (raw)
In-Reply-To: <21220.1208201514@sss.pgh.pa.us>
References: <48032021.90704@gmail.com>
<87r6d8hfgw.fsf@oxford.xeocode.com>
<21220.1208201514@sss.pgh.pa.us>
"Tom Lane" <tgl@sss.pgh.pa.us> writes:
> Gregory Stark <stark@enterprisedb.com> writes:
>> The transition domain where performance drops dramatically as the database
>> starts to not fit in shared buffers but does still fit in filesystem cache.
>
> It looks to me like the knee comes where the DB no longer fits in
> filesystem cache.
That does seem to make a lot more sense. I think I misread the units of the
size of the accounts table. Reading it again it seems to be in the 1.5G-2G
range for the transition which with indexes and other tables might be starting
to stress the filesystem cache -- though it still seems a little low.
I think if I squint I can see another dropoff at the very small scaling
numbers. That must be the point where the database is comparable to the shared
buffers size. Except then I would expect the green and blue curves to be
pushed to the right a bit rather than just havin a shallower slope.
--
Gregory Stark
EnterpriseDB http://www.enterprisedb.com
Ask me about EnterpriseDB's On-Demand Production Tuning
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To: pgsql-performance@postgresql.org
Cc: stark@enterprisedb.com, tgl@sss.pgh.pa.us, mendola@gmail.com
Subject: Re: shared_buffers performance
In-Reply-To: <874pa4gqea.fsf@oxford.xeocode.com>
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