 T1 reads a row. Another
 transaction T2 then modifies or deletes that row, before T1 has
 committed or rolled back.
 </ul>

 <p> A lock with <code>LockModeType.PESSIMISTIC_WRITE</code> can be obtained on
 an entity instance to force serialization among transactions
 attempting to update the entity data. A lock with
 <code>LockModeType.PESSIMISTIC_READ</code> can be used to query data using
 repeatable-read semantics without the need to reread the data at
 the end of the transaction to obtain a lock, and wi