Performance-Related Features

The Enterprise Server provides the following features to enhance performance or allow more fine-grained data checking. These features are supported only for entity beans with container managed persistence.

• Version Column Consistency Checking

• Relationship Prefetching

• Read-Only Beans

• Default Fetch Group Flags

Version Column Consistency Checking

The version consistency feature saves the bean state at first transactional access and caches it between transactions. The state is copied from the cache instead of being read from the database. The bean state is verified by primary key and version column values at flush for custom queries (for dirty instances only) and at commit (for clean and dirty instances).

To Use Version Consistency

1. Create the version column in the primary table.

2. Give the version column a numeric data type.

3. Provide appropriate update triggers on the version column.

   These triggers must increment the version column on each update of the specified row.

4. Specify the version column.

   This is specified in the check-version-of-accessed-instances subelement of the consistency element in the sun-cmp-mappings.xml file. See consistency in Sun GlassFish Enterprise Server v3 Application Deployment Guide.

5. Map the CMP bean to an existing schema.

   Automatic schema generation is not supported for beans with version column consistency checking. Instead, work with your database administrator to create the schema and add the required triggers.

Relationship Prefetching

In many cases when an entity bean’s state is fetched from the database, its relationship fields are always accessed in the same transaction. Relationship prefetching saves database round trips by fetching data for an entity bean and those beans referenced by its CMR fields in a single database round trip.

To enable relationship prefetching for a CMR field, use the default subelement of the fetched-with element in the sun-cmp-mappings.xml file. By default, these CMR fields are prefetched whenever findByPrimaryKey or a custom finder is executed for the entity, or when the entity is navigated to from a relationship. (Recursive prefetching is not supported, because it does not usually enhance performance.) See fetched-with in Sun GlassFish Enterprise Server v3 Application Deployment Guide.

To disable prefetching for specific custom finders, use the prefetch-disabled element in the sun-ejb-jar.xml file. See prefetch-disabled in Sun GlassFish Enterprise Server v3 Application Deployment Guide.

Multilevel relationship prefetching is supported for CMP 2.1 entity beans. To enable multilevel relationship prefetching, set the following property using the asadmin create-jvm-options command:

asadmin create-jvm-options -Dcom.sun.jdo.spi.persistence.support.sqlstore.MULTILEVEL_PREFETCH=true

Read-Only Beans

Another feature that the Enterprise Server provides is the read-only bean, an entity bean that is never modified by an EJB client. Read-only beans avoid database updates completely.

A read-only bean can be used to cache a database entry that is frequently accessed but rarely updated (externally by other beans). When the data that is cached by a read-only bean is updated by another bean, the read-only bean can be notified to refresh its cached data.

The Enterprise Server provides a number of ways by which a read-only bean’s state can be refreshed. By setting the refresh-period-in-seconds element in the sun-ejb-jar.xml file and the trans-attribute element (or @TransactionAttribute annotation) in the ejb-jar.xml file, it is easy to configure a read-only bean that is one of the following:

• Always refreshed

• Periodically refreshed

• Never refreshed

• Programmatically refreshed

Access to CMR fields of read-only beans is not supported. Deployment will succeed, but an exception will be thrown at runtime if a get or set method is invoked.

Read-only beans are best suited for situations where the underlying data never changes, or changes infrequently. For further information and usage guidelines, see Using Read-Only Beans.