On Sat, Aug 04, 2007 at 11:39:31PM +0200, Adriaan van Os wrote: > Kevin Grittner wrote: > >>>>On Mon, Jul 16, 2007 at 7:18 PM, in message > >>>><25418.1184631498@xxxxxxxxxxxxx>, > >Tom Lane <tgl@xxxxxxxxxxxxx> wrote: > >>Somehow, autovac is doing something that makes the filesystem go nuts > >>every so often, and take an astonishingly long time to create an empty > >>file. But autovac itself doesn't create or delete any files, so what's > >>up here? > > > >Have you ruled out checkpoints as the culprit? > > That's a good question. I will do some more tests, but I also suspect fsync > "cascading" > <http://www.uwsg.iu.edu/hypermail/linux/kernel/0708.0/1435.html>. Interesting. I'm guessing that ext3 has to sync out the entire journal up to the point in time that fsync() is called, regardless of what files/information the journal contains. Fortunately I think it's common knowledge to mount PostgreSQL filesystems with data=writeback, which hopefully eliminates much of that bottleneck... but if you don't do noatime you're probably still spewing a lot out to the drive. -- Decibel!, aka Jim Nasby decibel@xxxxxxxxxxx EnterpriseDB http://enterprisedb.com 512.569.9461 (cell)
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