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From: Tom Lane <[email protected]>
To: Christian Bucanac <[email protected]>
Cc: Pgsql-General (E-mail) <[email protected]>
Subject: Re: Performance tuning for linux, 1GB RAM, dual CPU?
Date: Wed, 11 Jul 2001 12:51:59 -0400
Message-ID: <[email protected]> (raw)
In-Reply-To: <5146853DD571D411AC54000102070D611C7F10@MINGBGNTS02>
References: <5146853DD571D411AC54000102070D611C7F10@MINGBGNTS02>

Christian Bucanac <[email protected]> writes:
>> I am going to try 768M (98304) for buffers and 6144 (6144 * 32 = 192M)
>> for sort mem. This way with the DB server serving a max of 32 application
>> servers the kernel and other processes should still have the last 64Mb RAM.

This is almost certainly a lousy idea.  You do *not* want to chew up all
available memory for PG shared buffers; you should leave a good deal of
space for kernel-level disk buffers.

Other fallacies in the above: (1) you're assuming the SortMem parameter
applies once per backend, which is not the case (it's once per sort or
hash step in a query, which could be many times per backend); (2) you're
not allowing *anything* for any space usage other than shared disk
buffers and sort memory.

The rule of thumb I recommend is to use (at most) a quarter of real RAM
for shared disk buffers.  I don't have hard measurements to back that
up, but I think it's a lot more reasonable as a starting point than
three-quarters of RAM.

			regards, tom lane

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