2010/2/18 Fujii Masao <masao.fu...@gmail.com>: > On Thu, Feb 18, 2010 at 7:04 PM, Heikki Linnakangas > <heikki.linnakan...@enterprisedb.com> wrote: >> Magnus Hagander wrote: >>> O_DIRECT helps us when we're not going to read the file again, because >>> we don't waste cache on it. If we are, which is the case here, it >>> should be really bad for performance, since we actually have to do a >>> physical read. >>> >>> Incidentally, that should also apply to general WAL when archive_mdoe >>> is on. Do we optimize for that? >> >> Hmm, no we don't. We do take that into account so that we refrain from >> issuing posix_fadvice(DONTNEED) if archive_mode is on, but we don't >> disable O_DIRECT. Maybe we should.. > > Since the performance of WAL write is more important than that of WAL > archiving in general, that optimization might offer little benefit.
Well, it's going to make the process that reads the WAL cause actual physical I/O... That'll take a chunk out of your total available I/O, which is likely to push you to the limit of your I/O capacity much quicker. -- Magnus Hagander Me: http://www.hagander.net/ Work: http://www.redpill-linpro.com/ -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
