Persisting a domain model with JDO 2.0 - POJOs in Action: Developing Enterprise Applications with Lightweight Frameworks - page 191

list of field names. PlaceOrderFieldProxyCreator applies the KodoFetch-
GroupInterceptor to the PlaceOrderService .
Each time the PlaceOrderService is called, the KodoFetchGroupIntercep-
tor will add the specified fields to the FetchConfiguration , which will cause
them to be eagerly loaded. If the UI design changes and requires different fields
to be loaded, you will just need to edit the Spring bean definition and not modify
any code.
You will be able to configure JDO 2.0 fetch groups using a similar AOP -based
approach. Instead of configuring individual fields, the interceptor will use the
JDO 2.0 API s to configure the active fetch groups. Eager loading is only one way to
improve performance. Another option is to use process-level caching.

5.4.2 Using a PersistenceManagerFactory-level cache

By default, a JDO implementation only caches objects in PersistenceManager . It
looks in the PersistenceManager cache before loading an object from the data-
base. In addition to ensuring that there is at most one in-memory representation
of a persistent object, the cache improves performance by reducing database
accesses. However, the PersistenceManager cache is flushed when a transaction
ends, which means that the next time the application accesses an object the JDO
implementation has to load it from the database. In a JDO application, you can
often improve performance significantly by caching frequently accessed but rarely
modified objects in the PersistenceManagerFactory -level cache, which is JDO' s
way of providing process-level caching.

Overview of the PersistenceManagerFactory-level cache
The JDO implementation looks in the PersistenceManagerFactory -level cache
after checking the PersistenceManager cache but before accessing the database.
This cache is not flushed when a transaction commits and consequently contains
objects accessed by multiple transactions. Enabling the PersistenceManager-
Factory -level cache can often increase performance significantly by reducing the
number of database accesses.
The JDO specification does not define the detailed behavior of the Persis-
tenceManagerFactory -level cache or how to configure it. You must typically con-
figure the cache by using a combination of vendor-specific Persistence-
ManagerFactory properties and XML metadata. For example, the Kodo JDO
PersistenceManagerFactory cache is enabled using the following Persis-
tenceManagerFactory properties: