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Re: General performance questions about postgres on Apple

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Sean Shanny <shannyconsulting(at)earthlink(dot)net>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: General performance questions about postgres on Apple
Date: 2004-02-23 03:24:29
Message-ID: 20382.1077506669@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-performance
Sean Shanny <shannyconsulting(at)earthlink(dot)net> writes:
> We have the following setting for random page cost:
> random_page_cost = 1            # units are one sequential page fetch cost
> Any suggestions on what to bump it up to?

Well, the default setting is 4 ... what measurements prompted you to
reduce it to 1?  The particular example you showed suggested that the
true value on your setup might be 10 or more.

Now I would definitely not suggest that you settle on any particular
value based on only one test case.  You need to try to determine an
appropriate average value, bearing in mind that there's likely to be
lots of noise in any particular measurement.

But in general, setting random_page_cost to 1 is only reasonable when
you are dealing with a fully-cached-in-RAM database, which yours isn't.

			regards, tom lane

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