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Re: old server, new server, same performance

From: Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>
To: Piotr Legiecki <piotrlg(at)ams(dot)edu(dot)pl>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: old server, new server, same performance
Date: 2010-05-17 08:10:58
Message-ID: AANLkTilnF7pHezPdQjvoKq8slPr34uG_ZoSTv1ntKxi_@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
On Mon, May 17, 2010 at 2:06 AM, Piotr Legiecki <piotrlg(at)ams(dot)edu(dot)pl> wrote:
> 2. select count(*) from some_table; runs in a fraction of a second on the
> console on both servers (there are only 4000 records, the second longer
> table has 50000 but it does not matter very much). From pg_admin the results
> are:
> - slow server (and the longest table in my db) 938ms (first run) and about
> 40ms next ones
> - fast server 110ms first run, about 30ms next ones.
> Well, finally my new server deservers its name ;-) The later times as I
> understand are just cache readings from postgresql itself?
SNIP
> So the server itself seems faster.
> So still I don't get this: select * from table; on old server takes 0,5 sec,
> on new one takes 6sec. Why there is so big difference? And it does not
> matter how good or bad select is to measure performance, because I don't
> measure  the performance, I measure the relative difference. Somwhere there
> is a bottleneck.

Yep, the network I'd say.  How fast are things like scp between the
various machines?

> 4. Machine. The new server has 5 SAS disks (+ 1 spare), but I don't remember
> how they are set up now (looks like mirror for system '/' and RAID5 for rest
> - including DB). size of the DB is 405MB

Get off of RAID-5 if possible.  A 3 Disk RAID-5 is the slowest
possible combination for RAID-5 and RAID-5 is generally the poorest
choice for a db server.

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