On Aug 17, 2011, at 2:14 PM, Scott Marlowe wrote: > On Wed, Aug 17, 2011 at 12:56 PM, Tomas Vondra <tv@xxxxxxxx> 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. I suppose this is my confusion. Or rather I am curious about this. On my current production database the pg_xlog directory is 8Gb (our total database is 200Gb). Does this warrant a totally separate setup (and hardware) than PGDATA? -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
