QUESTION POSED ON: 18 March 2005
Are there any clustering mechanism available at the Oracle application server (middle-tier level), such as in the DBMS level? We want to implement Oracle AS10g in more than one machine, as a cluster. That way if one machine crashes, the other can work without affecting the users' transactions.
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This is a big question. There are multiple levels of clustering on Oracle AS10g. Instances can be clustered so that changes made to one (deploying an application, configuration. etc) are applied to all instance in the cluster. At the OC4J level, there are islands. An island is a cluster of OC4J containers that replicate object state to all the containers in the island. If a request is made to a container that crashes to the container, a second request will be routed to another container in the island where it will find the objects in the last state and the application can continue to run. Note that the application my resent the request after the first request failed. This is explained in more detail in the Oracle documentation and in the Oracle 10g Application Server Administration Handbook by Oracle Press, of which I am one of the authors.
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