[Mono-aspnet-list] issues with intermittent apache hangups

Dan parnham at gmail.com
Fri Jul 22 05:32:22 EDT 2011

An update on where we are with this issue!

The libraries that we are now using are as follows:
mono 2.10.2
fluent nhibernate 1.2 (nhibernate 3.1)

We've spent the past couple of months trying to figure out why our
applications are leaking memory and have found a few worrying issues. I
won't go into details about some of the problems we've seen but will
concentrate on the leaks since they cause the web applications to gradually
grind to a halt.

I developed a test application (MVC 2 & 3) which contained some simple
javascript to poll the server very quickly. Monitoring this with the mono
profiler we found that it never seemed to be garbage collecting the
CacheItems. However it didn't leak at the same rate as our full web
applications so something else was going on too.

Finally with a lot of experimentation we have found that if we switch our
web applications to sessionless (sessionState mode="Off" in Web.config) they
no longer seemed to leak CacheItems and we found that running nhibernate in
"thread_static" mode did not seem to leak but "web" did. Since we couldn't
leave it as thread_static for the web applications we switched to our own
simplified CurrentSessionContext implementation. 

With those changes our web applications appeared to no longer leak, but in
fact the applications stopped leaking when running in XSP and as soon as we
deploy to mod_mono they happily start chewing up memory again.

We are also developing a daemon to run alongside the web applications that
uses the same fluent based data provider as the web application (although
running in thread_static mode) and the memory usage for that appears to be
solid, so we know it is not a problem with our data provider implementation.
All the evidence seems to point towards the System.Web related libraries
(with hints of CacheItem and HashMap thrown in), but we are not familiar
enough with how it all works to even know where to begin looking, and
frankly we've wasted too much time on this already.

We have been trying to solve these issues for so long now that we're having
to seriously consider deploying to .NET, despite the fact that we've
invested a lot of time in building a linux-based server module for the
daemon and web applications. 

If we are no longer seeing leaks using XSP, is there a possibility that we
could deploy our web application using that instead of mod_mono (by setting
up apache with mod_proxy)?


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