Aidan Van Dyk wrote:
Sure, if your WAL is on the same FS as your data, you're going to get hit, and *especially* on ext3... But, I think that's one of the reasons people usually recommend putting WAL separate.
Separate disks can actually concentrate the problem. The writes to the data disk by checkpoints will also have fsync behind them eventually, so splitting out the WAL means you just push the big write backlog to a later point. So less frequently performance dives, but sometimes bigger. All of the systems I was mentioning seeing >10 second pauses on had a RAID-1 pair of WAL disks split from the main array.
-- Greg Smith 2ndQuadrant Baltimore, MD PostgreSQL Training, Services and Support greg@xxxxxxxxxxxxxxx www.2ndQuadrant.com -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
