Re: old server, new server, same performance

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