On Mon, Jun 3, 2013 at 1:20 AM, Robert Haas <robertmh...@gmail.com> wrote: > On Sun, Jun 2, 2013 at 2:44 PM, Jeff Janes <jeff.ja...@gmail.com> wrote: >> Do we know why anti-wraparound uses so many resources in the first place? >> The default settings seem to be quite conservative to me, even for a system >> that has only a single 5400 rpm hdd (and even more so for any real >> production system that would be used for a many-GB database). >> >> I wonder if there is something simple but currently unknown going on which >> is causing it to damage performance out of all proportion to the resources >> it ought to be using. > > I can't rule that out. Personally, I've always attributed it to the > fact that it's (a) long and (b) I/O-intensive. But it's not > impossible there could also be bugs lurking.
It could be related to the OS. I have no evidence for or against, but it's possible that OS write-out routines defeat the careful cost based throttling that PostgreSQL does by periodically dumping a large portion of dirty pages into the write queue at once. That does nasty things to query latencies as evidenced by the work on checkpoint spreading. Regards, Ants Aasma -- Cybertec Schönig & Schönig GmbH Gröhrmühlgasse 26 A-2700 Wiener Neustadt Web: http://www.postgresql-support.de -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers