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@xxxxxxxxxxxxx http://www.gregsmith.com Baltimore, MD
