3.5.1 Dependent Data Service Using Another Back-End Data Service

Some data services store no data directly themselves, but instead depend upon another back-end data service to store all their data. Such a data service translates all read and update requests into calls on the back-end data service. For example, consider a hypothetical client-server appointment calendar service that keeps all of its data in an SQL database such as Oracle. The appointment calendar service has its own client-server network protocol. For example, it might have defined its protocol using an RPC specification language, such as ONC^TM RPC.

In the Sun Cluster environment, you can use HA-DBMS for ORACLE7 to make the back-end Oracle database highly available. Then, you can write simple methods for starting and stopping the appointment calendar daemon. You can register the appointment calendar data service with Sun Cluster as one that depends upon another Sun Cluster data service, HA-DBMS for ORACLE7. Specify this dependency using the -d option to hareg(1M).

The start method for Oracle might initiate only database recovery and might not wait for the recovery to complete. Therefore, our calendar data service daemon, once it has been started, must poll waiting for the Oracle database to become available.