thout blocking
 other transactions reading the data. A lock with
 <code>LockModeType.PESSIMISTIC_WRITE</code> can be used when querying data and
 there is a high likelihood of deadlock or update failure among
 concurrent updating transactions.
 
 <p> The persistence implementation must support use of locks of type
 <code>LockModeType.PESSIMISTIC_READ</code> 
 <code>LockModeType.PESSIMISTIC_WRITE</code> on a non-versioned entity as well as
 on a versioned entity.

 <p> When the lock cannot be obtained, and t