Greg Stark escribió: > On Tue, Mar 16, 2010 at 2:30 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: > > "Pierre C" <li...@peufeu.com> writes: > >> Does PG issue checkpoint writes in "sorted" order ? > > > > No. IIRC, a patch for that was submitted, and rejected because no > > significant performance improvement could be demonstrated. We don't > > have enough information about the actual on-disk layout to be very > > intelligent about this, so it's better to just issue the writes and > > let the OS sort them. > > Keep in mind that postgres is issuing writes to the OS buffer cache. > It defers fsyncing the files as late as it can in the hopes that most > of those buffers will be written out by the OS before then. That gives > the OS a long time window in which to flush them out in whatever order > and whatever schedule is most convenient.
Maybe it would make more sense to try to reorder the fsync calls instead. -- Alvaro Herrera http://www.CommandPrompt.com/ The PostgreSQL Company - Command Prompt, Inc. -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
