I had a server constantly running out of memory and I just couldn't figure out what was wrong. The first thing I did, thanks to Steven Erat, was enable the jrun metrics to monitor threads, sessions, and jvm memory. You do this by editing the \runtime\servers\coldfusion\SERVER-INF\jrun.xml and set <attribute name="metricsEnabled">true</attribute>. I debugged my caching system, fixed some garbage collection issues, but it still did not completely fixed my problem.
A few days later, I got an insight: the onSessionStart and onSessionEnd functions.
I had the following functions defined:
<!--- on Session Start --->
<cffunction name="onSessionStart">
<cfscript>
application.com.objectFactory.getInstance('session').addSession(session);
</cfscript>
</cffunction>
<!--- on Session End --->
<cffunction name="onSessionEnd">
<cfargument name="SessionScope" required="Yes" />
<cfargument name="ApplicationScope" required="No" />
<cfscript>
ApplicationScope.com.objectFactory.getInstance('session').delSession(arguments.SessionScope.sessionId);
</cfscript>
</cffunction>
Well, guess what, it seems like even after removing the reference to the specific session, ColdFusion failed to destroy it. I would have assumed that ColdFusion would just destroy the session, and if I happen to still be pointing to it I would get the famous null pointer exception, but no, ColdFusion kept a copy of some sort draining all my memory. As soon as I removed the reference to the session, the jrun garbage collection did its job and memory because stable again.
I will try to look further into this behavior using the Scorpio Server Monitoring, which includes really nice tools to analyze what's using your precious RAM.
