Read-Mostly Pattern

Chapter 8 Creating J2EE Applications for BEA WebLogic

Read-Mostly Pattern

WebLogic Server does not support a read-mostly cache strategy setting in weblogic-ejb-jar.xml. However, if you have EJB data that is only occasionally updated, you can create a "read-mostly pattern" by implementing a combination of read-only and read-write EJBs.

In a read-mostly pattern, a read-only entity EJB retrieves bean data at intervals specified by read-timeout-seconds. A separate read-write entity EJB models the same data as the read-only EJB, and updates the data at required intervals. See the read-mostly EJB example in the WebLogic Server distribution for more information.

When creating a read-mostly pattern, use the following suggestions to reduce the likelihood of data consistency problems:

For all read-only EJBs, set read-timeout-seconds to the same value for all beans that may be updated in the same transaction.
For all read-only EJBs, set read-timeout-seconds to the smallest timeframe that yields acceptable performance levels.
Ensure that all read-write EJBs in the system update only the smallest portion of data necessary; avoid beans that write numerous, unchanged fields to the datastore at each ejbStore().
Ensure that all read-write EJBs update their data in a timely fashion; avoid involving read-write beans in long-running transactions that may span the read-timeout-seconds setting for their read-only counterparts.

Note that in a WebLogic Server cluster, clients of the read-only EJB benefit from using cached EJB data. Clients of the read-write EJB benefit from true transactional behavior, since the read-write EJB's state always matches the state of its data in the underlying datastore. See Entity EJBs in a Cluster for more information.