Manik,

Many thanks for your reply - just to let you know we found out what the problem 
was.

We have a listener attached to each cache which helps us manage indexes on the 
cache (we index some entities to prevent us having to traverse the all the 
entities when retrieving a selection of items - through jboss cache we have 
pretty much killed off any need to access the database with the exception of 
the inital load, writes and updates)

Within the listener there was a HashMap instance variable - it was this 
variable which was causing JVM to lock up - when we did a thread dump we 
noticed that the replication thread was getting stuck on the put method of this 
HashMap at the same time as another normal application thread was - hence the 
replication queue was backing up and causing the replication exceptions to be 
thrown to the other nodes on the cluster. Searching the net I found a number of 
instances where hashmap can spin out of control if two thread hit the rebuild 
method of the hashmap. We have since adding read/write lock to this variable 
and we have yet to experience this issue again. Unfortunately it was fairly 
hard to find as you would have expected to see a deadlock - and it was only 
when we did a number of thread over a minute that we picked this up.

We have briefly tried the version three and things seem go really well until 
ramped up the load on the clustered cache (the local caches where absolutely 
flying) it started to through lock errors (which was actually the last issue I 
was expecting given the new locking system - before pointing the figure at the 
new version I want to do more analysis at our end as it could be some silly 
code at our end or the database running really slowly).

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