As long as I know there are generally two methods of synchronization
in distributed environments:
1- Shared memory
2- Messaging
The first method is usually faster in small clusters, but it has a two
disadvantages you can't have benefits of clustering failover, in large
number of servers this shared memory becomes the bottleneck.
Second methods is usually slower but if implemented correctly it may
enable you to have a cluster of equal servers with fail over benefits,
and the performance is not dropping much by increase in number of servers.
I want to know what method is every one using and compare odds and
even of those methods in an article, but it looks like except few
developers must of them are totally ignoring the synchronization  issue!
I want to ask EJB 3.0 spec members to clarify synchronization
mechanism of j2ee.
Do you have any suggestions on this?