30.4. Entity Bean Locking and Deadlock Detection

This section provides information on what entity bean locking is and how entity beans are accessed and locked within JBoss. It also describes the problems you may encounter as you use entity beans within your system and how to combat these issues. Deadlocking is formally defined and examined. And, finally, we walk you through how to fine tune your system in terms of entity bean locking.

30.4.1. Why JBoss Needs Locking

Locking is about protecting the integrity of your data. Sometimes you need to be sure that only one user can update critical data at one time. Sometimes, access to sensitive objects in your system need to be serialized so that data is not corrupted by concurrent reads and writes. Databases traditionally provide this sort of functionality with transactional scopes and table and row locking facilities.
Entity beans are a great way to provide an object-oriented interface to relational data. Beyond that, they can improve performance by taking the load off of the database through caching and delaying updates until absolutely needed so that the database efficiency can be maximized. But, with caching, data integrity is a problem, so some form of application server level locking is needed for entity beans to provide the transaction isolation properties that you are used to with traditional databases.