[rules-users] ArrayIndexOutOfBounds when calling addKnowledgePackage?

[malkhafaji]

For those that are interested. I solved the problem. Basically I got over the
following inherent problems in Drools (not that they are bugs, but they did
not suit my application requirements):

1. A new class loader for each KnowledgeBase. This caused about 20-30K
classes loaded per KnowledgeBase causing me the Perm gen errors. If I
increased the Perm gen memory parameters, I got hit on the native thread
creation issue (the more memory your application consumes, the less threads
you can instantiate because you will have less memory to work with).

2. The time taken to compile the KnowledgePackages AND to add them to each
KnowledgeBase.

So, what I did was a combination of a few things:

1. I created one KnowledgeBase and loaded all the KnowledgePackages that I
needed to load in it. Serialized it to a file. And retrieved X instances and
added them to a pool. Now, I have X KnowledgeBase instances without the
heavy class loading that comes with creating each one if you use the regular
way of creating it from scratch. When you de-serialize it, there are a lot
less classes loaded. Doing this also allowed me to avoid compiling the
KnowledgePackages on start up, and now my application starts up immediately
like a bullet :)

2. I changed some of my JVM parameters to add very aggressive GC parameters.
The fact that I was able to avoid using many class loaders for each
instantiation of a KnowledgeBase allowed me to reduce the Perm Gen memory
setting which allowed me more memory for my threads :) my application is
actually thread heavy, and why not when we have an 8-core server!!

I am using the following JVM parameters for anyone interested:

-XX:+CMSClassUnloadingEnabled -XX:+UseParallelOldGC -XX:ParallelGCThreads=8

You can look up their definitions. Now I am golden!!! 
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