Whoops, wrong thread.
On Mon, May 17, 2010 at 2:52 AM, Scott Marlowe <scott.marlowe@gmail.com> wrote:
> On Mon, May 17, 2010 at 2:10 AM, Scott Marlowe <scott.marlowe@gmail.com> wrote:
>> On Mon, May 17, 2010 at 2:06 AM, Piotr Legiecki <piotrlg@ams.edu.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@postgresql.org/msg93043.html
