On Mon, 2006-06-26 at 08:59, Tony Caduto wrote: > MG wrote: > > Hello, > > > > we are using PostgreSQL 8.0.3 together with RAID on OpenServer 6. > > > > When we do a big SELECT-query the whole maschine becomes very very > > very slowly or stands. > > The maschine has 3 GB RAM, so we suppose it`s the RAID. > > > > Has anyone some experience with RAID + PostgreSQL? > > > > Where does PostgreSQL saves his temporary files? Perhaps these are the > > reason for the bad performance. > > > > Greetings > > > > Michaela > What kind of RAID? I know if you have it set up to mirror it becomes > slow as pond water.
I have to say this has NOT been my experience. With a pair of U320 drives on an LSI-Megaraid with battery backed cache (256M or 512M, not sure which it was, it's been a few years) our pg server was noticeable faster with a mirror set than with a single IDE drive (with cache disabled) on the same machine. And faster than a single SCSI drive with no RAID controller as well. > I have a server that was a hand me down so I did not have a choice in > the RAID and it was set up to mirror with two drives and > the performance on large selects was very bad. Wow, something's wrong then. normally, selects are much faster on mirror sets rather than on a single drive. Do you have a lot of sorts spilling onto disc? > The performance would > increase by 50 or more percent if > fsync = off is set in the postgresql.conf file. Of selects? Or performance in general? I can see if for performance in general, but selects really shouldn't be greatly affected by fsync. In another vein, I agree with Joshua. There could be LOTS of causes of poor performance. I wouldn't just assume it's RAID until it's been proven to be the cause of the problem. ---------------------------(end of broadcast)--------------------------- TIP 6: explain analyze is your friend
