[pmwiki-users] pmwiki.org web server instability

Patrick R. Michaud pmichaud at pobox.com
Fri May 28 17:48:06 CDT 2010

On Fri, May 28, 2010 at 10:46:20AM -0400, DaveG wrote:
> Same -- large number of timeouts, usually lasting around 5-10
> minutes. Several per day, over the last 10 days or so.

The virtual private server (VPS) software that pmwiki.org is under
watches memory usage, and when it exceeds a certain threshhold limit 
(burst mode) the controller starts killing off processes somewhat randomly
to bring total memory usage back under the limit.  Other processes
run from time to time to bring key services (such as the webserver)
back online if they were killed.

I've never been able to determine exactly what causes the server to
hit the limits.  I know that some of the automated cpanel updates
and system maintenance utilities often cause the memory limit
to be exceeded (which I find frankly annoying, since I don't have
much control over those).

Also, if pmwiki.org (or the other sites I host on the VPS) gets 
flooded with a lot of HTTP requests (e.g. from poorly-behaved spiders) 
then memory usage can go up dramatically as well.  This is especially
true if those requests are for things like pagelists and search
results that require a lot of memory to generate.

I just checked with my service provider, and they apparently have
new hosting packages that eliminate the burst mode problem and are 
also $30/mo *cheaper* than what I currently have.  So, the solution 
looks to me like I should migrate pmwiki.org and my other sites
to a new server package, and this should resolve a lot of our 
service issues.  (It would also upgrade me to later versions
of the OS and control panels and give me a good reason to clean
up many things on the overall system, which should increase 
security and performance a fair bit.)

I'll work on that over the next few days.


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