On Oct 30, 2012, at 12:12 PM, David Gerard <dgerard(a)gmail.com> wrote:
On 29 October 2012 23:56, Dave Humphrey
<dave(a)uesp.net> wrote:
As a rough guess at what to set MaxClients to use
"top" and look at the
difference between the RES and SHR columns of all httpd processes. I
believe this is roughly the amount of non-shared memory each of the child
Apache processes are using (for example, I'm averaging 10 MB per process).
Take the maximum amount of RAM you want Apache to use and divide it by this
memory to get a rough number for MaxClients. You can monitor memory usage
and adjust this as needed or through load testing.
I just set MaxClients 50 (on the basis of fat apache2 processes having
~50MB discrepancy between RES and SHR). Let's see what happens.
Of course, this is a solution to the usage of
swap and not the actual issue
you are having. I would continue to look at what is causing the surge in
requests. Is it a DoS of some sort (either accidental or on purpose) or is
some part of the server stalling which is causing requests to pile up and
overflow? For example, if the database is having an issue (a bunch of long
queries) then all Apache requests will start piling up until you hit swap
or the database issue resolves itself.
I see that in busy times, the CPU usage goes way up and a chunk of it
is MySQL. I could be wrong, but this suggests to me complex requests
to MediaWiki (e.g. logged in editors right-clicking diffs on an
obscure page). I should probably profile MediaWiki, given we have a
pile of custom extensions.
Along these lines I would suggest some sort of
monitoring/logging service
like Zabbix or Nagois (to name just two, there are many similar options to
choose from). This helps you on two fronts: 1) Logging of Parameters and 2)
I live on our Munin graphs :-)
I know it's heretically commercial software, but I believe in and have used New Relic
at several client sites, and their free "lite" service level might well help
diagnose further...
George William Herbert
Sent from my iPhone
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