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'''In progress'''
==How to use EclispeLink Caching==
==How to use EclispeLink Caching==

Revision as of 11:31, 25 November 2009

How to use EclispeLink Caching

By default EclipseLink uses a shared object cache, that caches a subset of all objects read and persisted for the persistence unit. The EclipseLink shared cache differs from the local EntityManager cache. The shared cache exists for the duration of the persistence unit (EntityManagerFactory, or server) and is shared by all EntityManagers and users of the persistence unit. The local EntityManager cache is not shared, and only exists for the duration of the EntityManager or transaction.

The benefit of the shared cache, is that once an object has been read, if it is read again using the find operation, the database does not need to be accessed. Also if the object is read through any Query, it will not need to be rebuilt, and its relationships will not need to be re-fetched.

The limitation of the shared cache, is that if the database is changed directly through JDBC, or by another application or server, the objects in the shared cache will be stale.

EclipseLink offers several mechanism to deal with stale data including:

  • Refreshing
  • Invalidation
  • Optimistic locking
  • Cache coordination

The shared cache can also be disabled. This can be done using the persistence unit property:

<property name="eclipselink.cache.shared.default" value="false"/>

Or can be selectively enabled/disabled using the @Cache annotation.

EclipseLink also offers several different caching strategies, the configure how many objects are cached, and how much memory is used.

Note, the CacheType NONE should not be used to disable the cache, instead shared should be set to false.

See Introduction to Cache for details on these types.

Using the @Cache Annotation

You may define the @Cache annotation on the following:

  • @Entity
  • @MappedSuperclass;
  • the root of the inheritance hierarchy (if applicable).

If you define the @Cache annotation on an inheritance subclass, the annotation will be ignored. If you define the @Cache annotation on @Embeddable EclipseLink will throw an exception.

Example of @Cache Annotation

  type=CacheType.SOFT, // Cache everything until the JVM decides memory is low.
  size=64000  // Use 64,000 as the initial cache size.
  expiry=36000000,  // 10 minutes
  coordinationType=CacheCoordinationType.INVALIDATE_CHANGED_OBJECTS  // if cache coordination is used, only send invalidation messages.
public class Employee {

Attributes of the @Cache Annotation

Attribute Description Default Required or Optional Override with Persistence Unit Property


Set this attribute to the type (org.eclipse.persistence.annotations.CacheType enumerated type) of the cache that you will be using:

  • FULL
  • WEAK
  • SOFT
  • NONE



  • eclipselink.cache.type.<ENTITY>
  • eclipselink.cache.type.default


Set this attribute to an int value to define the size of cache to use (number of objects).



Indicate whether cached instances should be in the shared cache or in a client isolated cache (see Isolated Client Session Cache).

  • true - use shared cache for cached instances;
  • false - use client isolated cache for cached instances.




The int value to enable the expiration of the cached instance after a fixed period of time (milliseconds). Queries executed against the cache after this will be forced back to the database for a refreshed copy.

-1 (no expiry)



Specific time of day (org.eclipse.persistence.annotations.TimeOfDay) when the cached instance will expire. Queries executed against the cache after this will be forced back to the database for a refreshed copy.




Set to a boolean value of true to force all queries that go to the database to always refresh the cache.




Set to a boolean value of true to force all queries that go to the database to refresh the cache only if the data received from the database by a query is newer than the data in the cache (as determined by the optimistic locking field).

Note: This option only applies if one of the other refreshing options, such as alwaysRefresh, is already enabled.

Note: A version field is necessary to apply this feature.




Set to a boolean value of true to force all queries to bypass the cache for hits, but still resolve against the cache for identity. This forces all queries to hit the database.




Set this attribute to the cache coordination mode (org.eclipse.persistence.annotations.CacheCoordinationType enumerated type).



Caching in Clustered Environments

Relevant API