Controlling concurrent access locks. This is (Web host music) almost always
Controlling concurrent access locks. This is almost always a performance bottleneck; every data access involves additional lock checks to a synchronized lock manager. Optimistic locking, however, is the perfect concurrency control strategy and performs well in long-running conversations. Depending on your conflict-resolution options (that is, if you had enough time to implement merge changes), your application users are as happy with it as with blocked concurrent access. They may also appreciate not being locked out of particular screens while others look at the same data. Java Persistence defines LockModeType.READ for the same purpose, and the EntityManager also has a lock() method. The specification doesn t require that this lock mode is supported on nonversioned entities; however, Hibernate supports it on all entities, because it defaults to a pessimistic lock in the database. The Hibernate lock modes Hibernate supports the following additional LockModes: LockMode.NONE Don t go to the database unless the object isn t in any cache. LockMode.READ Bypass all caches, and perform a version check to verify that the object in memory is the same version that currently exists in the database. LockMode.UPDGRADE Bypass all caches, do a version check (if applicable), and obtain a database-level pessimistic upgrade lock, if that is supported. Equivalent to LockModeType.READ in Java Persistence. This mode transparently falls back to LockMode.READ if the database SQL dialect doesn t support a SELECT … FOR UPDATE option. LockMode.UPDGRADE_NOWAIT The same as UPGRADE, but use a SELECT … FOR UPDATE NOWAIT, if supported. This disables waiting for concurrent lock releases, thus throwing a locking exception immediately if the lock can t be obtained. This mode transparently falls back to LockMode.UPGRADE if the database SQL dialect doesn t support the NOWAIT option. LockMode.FORCE Force an increment of the objects version in the database, to indicate that it has been modified by the current transaction. Equivalent to LockModeType.WRITE in Java Persistence. LockMode.WRITE Obtained automatically when Hibernate has written to a row in the current transaction. (This is an internal mode; you may not specify it in your application.)
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