| From: | Jim Nasby <jim(at)nasby(dot)net> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Simon Riggs <simon(at)2ndquadrant(dot)com>, Greg Smith <greg(at)2ndquadrant(dot)com>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Spread checkpoint sync |
| Date: | 2011-01-17 23:07:38 |
| Message-ID: | 6CF4BB73-93EB-4036-AE89-F40A81A4DE97@nasby.net |
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| Lists: | pgsql-hackers |
On Jan 15, 2011, at 8:15 AM, Robert Haas wrote:
> Well, the point of this is not to save time in the bgwriter - I'm not
> surprised to hear that wasn't noticeable. The point is that when the
> fsync request queue fills up, backends start performing an fsync *for
> every block they write*, and that's about as bad for performance as
> it's possible to be. So it's worth going to a little bit of trouble
> to try to make sure it doesn't happen. It didn't happen *terribly*
> frequently before, but it does seem to be common enough to worry about
> - e.g. on one occasion, I was able to reproduce it just by running
> pgbench -i -s 25 or something like that on a laptop.
Wow, that's the kind of thing that would be incredibly difficult to figure out, especially while your production system is in flames... Can we change ereport that happens in that case from DEBUG1 to WARNING? Or provide some other means to track it?
--
Jim C. Nasby, Database Architect jim(at)nasby(dot)net
512.569.9461 (cell) http://jim.nasby.net
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