1 Feb
2010
1 Feb
'10
3:02 p.m.
** Hugo Mills <hugo-bf(a)carfax.org.uk> [2010-02-01 14:20]:
On Mon, Feb 01, 2010 at 03:07:26PM +0100, Conrad Wood
wrote:
<snip>
I'd say apache pid 27046 is waiting for IO
after it requested more
memory and the kernel trying to free some by utilising swap.
After 11 seconds (of doing IO) it complained.
_If_ my analysis is correct, you'd have the following Options:
* add more ram
* reduce amount of ram required
* increase IO Speed (new kernel/drivers/etc..)
* Reduce the footprint of Apache to fit in the RAM you've got.
What happens is, when you get spike in load (from a badly-written
spider, or a little light slashdotting), apache spawns more processes
to cope. This takes up RAM, and eventually pushes you into swap. Of
course, that then slows down the processing by several orders of
magnitude, ensuring that it falls even further behind, attempting to
spawn even more processes to keep up, and finally the system collapses
completely.
Bringing down the maximum number of processes that Apache will
consider serving so that they all fit in RAM prevents this from
happening.
<snip>
** end quote [Hugo Mills]
Interesting thought. I've been experiencing this sort of problem on a regular
basis, although not had the time to investigate. I've noted similar errors, but
not based on a specific application, and after finding some references to
problems with Ubuntu virtualisation with Xen have assumed that when I get round
to it I'll be looking for a base OS configuration issue.
I've migrated from another company who originally used UML, although they
experimented with Xen and seem to be useing KVM now. I believe I was still on
the UML setup, since I don't remember being advised of a mirgation. That ran
the same services with no problems on the same basic virtual hardware spec.
I really need to start investigating now as although I'm monitoring it, it is
far from ideal. Being impressed with a 2 day uptime is a sad state of affairs!
--
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