Re: dbt2 NOTPM numbers

On Tue, 5 Jun 2007, Markus Schiltknecht wrote:

> I'm really wondering, if the RAID 6 of the ARECA 1260 hurts so badly

All of your disk performance tests look reasonable; certainly not slow
enough to cause the issue you're seeing. The only thing I've seen in this
thread that makes me slightly suspicious is:

> Oh, something else that's probably worth thinking about (and just came
> to my mind again): the XFS is on a lvm2, on that RAID6.

There have been reports here from reliable sources that lvm can introduce
performance issues;
http://archives.postgresql.org/pgsql-performance/2006-07/msg00276.php is
one example. Your dd test results suggest you're getting decent thoughput
though, so you don't seem to be suffering too much from that.

Anyway, did you post your postgresql.conf yet? I don't remember seeing
it. From looking at your latest data, my first guess would be there's
something wrong there that's either causing a) the system to be
checkpointing constantly, or b) not enough memory allocated to allow
queries to execute properly. The fact that all your long statement times
come from SELECTs suggests to me that playing with the WAL parameters like
fsync isn't likely to help here.

--
* Greg Smith gsmith(at)gregsmith(dot)com http://www.gregsmith.com Baltimore, MD