[jbosscache-dev] Storing k, v at root node of marshaled region and cache loaders.

[Galder Zamarreno]

Hi all,

Yesterday while looking at a support case, I discovered an awkward 
behavior when it came to root region based marshalling nodes and cache 
loaders.

Let's say you have a cache configured with a cache loader and have a 
region marshaled called starting at /me. I have created an MBean so that 
I can register/unregister classloader and activate/deactivate the region 
upon deployment/undeployment of the classes I wanna put under /me.

Now, let's say that I put a k,v in /me which will get stored in the 
cache loader. If I know touch the deployment archive to force a 
redeployment and check the contents of the cache, they're empty. If I 
try to get the k I put under /me, it'll return nothing. Why?

Simple: The cache instance is configured to preload from root (/) but 
when the region is activated, /me node is created. When the preloading 
phase comes, a check is made to see whether the node needs to be loaded:

    private boolean mustLoad(DataNode n, Object key)
    {
       if (log.isTraceEnabled())
       {
          log.trace("mustLoad called with key=" + key + " and datanode=" 
+ n);
       }
       return n == null ||
               (n.containsKey(TreeCache.UNINITIALIZED) && (key == null 
|| !n.containsKey(key)));
    }

The problem is that nothing will be preloaded for at least the /me node, 
because the node is not null, and it's not TreeCache.UNINITIALIZED. Any 
child nodes under the region node do not have issues like this.

This is likely a bug: maybe when the region is activated, the node 
should probably be created as TreeCache.UNINITIALIZED? I think this 
would work).

It's true that you could say that putting data at the root node of the 
region is not a good idea regardless, but I think deep down this is a bug.

Thoughts?

p.s. This is at least present in 1.4.x, need to check trunk. However, 
wanted to gather some thoughts before I continue debugging/fixing it.
-- 
Galder Zamarreño
Sr. Software Maintenance Engineer
JBoss, a division of Red Hat