Java Persistence with Hibernate

10.2. Controlling concurrent access

Databases (and other transactional systems) attempt to ensure transaction isolation, meaning that, from the point of view of each concurrent transaction, it appears that no other transactions are in progress. Traditionally, this has been implemented with locking. A transaction may place a lock on a particular item of data in the database, temporarily preventing access to that item by other transactions. Some modern databases such as Oracle and PostgreSQL implement transaction isolation with multiversion concurrency control (MVCC) which is generally considered more scalable. We'll discuss isolation assuming a locking model; most of our observations are also applicable to multiversion concurrency, however.