On Wed, Aug 17, 2011 at 12:56 PM, Tomas Vondra <t...@fuzzy.cz> wrote: > > I think you've mentioned the database is on 6 drives, while the other > volume is on 2 drives, right? That makes the OS drive about 3x slower > (just a rough estimate). But if the database drive is used heavily, it > might help to move the xlog directory to the OS disk. See how is the db > volume utilized and if it's fully utilized, try to move the xlog > directory. > > The only way to find out is to actualy try it with your workload.
This is a very important point. I've found on most machines with hardware caching RAID and 8 or fewer 15k SCSI drives it's just as fast to put it all on one big RAID-10 and if necessary partition it to put the pg_xlog on its own file system. After that depending on the workload you might need a LOT of drives in the pg_xlog dir or just a pair. Under normal ops many dbs will use only a tiny % of a dedicated pg_xlog. Then something like a site indexer starts to run, and writing heavily to the db, and the usage shoots to 100% and it's the bottleneck. -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
