[Mono-dev] High Traffic Site (for Harry Potter 7) is crashing!

[Gonzalo Paniagua Javier]

On Tue, 2010-10-26 at 13:59 -0700, Matthew Urbano wrote:
> I've created a site for the new Harry Potter movie which is expected
> to get a high volume of traffic, and on launch day we are now
> crashing.

> We are getting the following errors on the webservers due to traffic:
> 
> Maximum number of concurrent mod_mono requests
> to /tmp/mod_mono_dashboard_default_2.lock reached (20 active, 20
> waiting). Request dropped.
> 
> I have the following config:
> 
> User nobody
> 
> Group nobody
> 
> include /etc/httpd/conf/mod_mono.conf
> 
> MonoSetEnv MONO_THREADS_PER_CPU=500

> And have also added this: 
> 
> MonoMaxActiveRequests 0
> 
> MonoMaxWaitingRequests 0

These settings should get rid of the warning after an apache restart.
Make sure there are no mod-mono-server processes around after you stop
apache.

If they don't work, try adding the optional server alias like this:
MonoMaxActiveRequests default 0
MonoMaxWaitingRequests default 0

Also add the server alias to MonoSetEnv.

> These settings do not seem to be taking affect.  What other steps
> should we take to allow mono to handle the traffic?

The real "fix" would be to upgrade to Mono 2.8. Those 3 settings were
recommended prior to mono 2.8 to be able to deal with high traffic due
to limitations in our thread pool implementation.

Mono 2.8+ has a new thread pool implementation and mod_mono 2.8+
defaults to 0 for those two MonoMax* directives (which should be
obsoleted soon).

Let us know if either adding the server alias or upgrading to mono 2.8
fixes your problem.

-Gonzalo