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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 08:53:49
Message-ID: AANLkTimNGmFIrYxIqmM73NahbTL1TYdBPYVghrsnEKvZ@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
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On Mon, May 17, 2010 at 2:52 AM, Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com> wrote:
> On Mon, May 17, 2010 at 2:10 AM, Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com> wrote:
>> 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.
>
> I refer you to this classic post on the subject:
> http://www.mail-archive.com/pgsql-general(at)postgresql(dot)org/msg93043.html

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