Core Java™ Data Objects

3.14. Concurrency Control

All the examples so far have been single-user applications (only one transaction was accessing the datastore at a time). It is, of course, possible for multiple applications to be running concurrently. The JDO specification does not make any specific statements about concurrency control, because it is a feature of the underlying datastore rather than of JDO itself.

JDO does define the concept of a datastore transaction and says that access to the datastore should be done within the context of a transaction and that these transactions should exhibit ACID properties. This allows the JDO implementation to use the underlying datastore's own concurrency control mechanisms, which may be based on a pessimistic or optimistic ...