Revision as of 15:41, 12 January 2011

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Examples

• Caching

Caching

The EclipseLink cache is an in-memory repository that stores recently read or written objects based on class and primary key values. EclipseLink uses the cache to do the following:

• Improve performance by holding recently read or written objects and accessing them in-memory to minimize database access.
• Manage locking and isolation level.
• Manage object identity.

For more information about the EclipseLink cache and its default behavior, see Introduction to Cache.

EclipseLink defines the following entity caching annotations:

• @Cache
• @TimeOfDay
• @ExistenceChecking

EclipseLink also provides a number of persistence unit properties that you can specify to configure the EclipseLink cache (see How to Use the Persistence Unit Properties for Caching). These properties may compliment or provide an alternative to the usage of annotations.

For more information, see the following:

• What You May Need to Know About Overriding Annotations in JPA
• What You May Need to Know About Using EclipseLink JPA Persistence Unit Properties

EclipseLink
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EclipseLink JPA Extensions for Entity Caching

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

...
@Entity
@Cache(
  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 {
  ...
}

Optimistic Locking	Basic JPA Development	Shared and Isolated
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