How Failover Works in a Rack-Mounted Directory Server Environment

In a rack-mounted environment, the OID Monitor on each node reports to the other nodes that it is running by sending a message to the Oracle9i Database Server every 10 seconds. When it does this, it also polls the database server to verify that all other directory server nodes are also running. If, after 250 seconds, an OID Monitor on one of the nodes has not reported that it is running, then the other directory server nodes regard it as having failed. At this point, the following occurs on one of the other nodes that are still running:

1. The OID Monitor on that node brings up the processes that were running on the failed node.

2. The directory server on that node continues processing the operations that were previously underway on the failed node.

3. The OID Monitor on that node logs that it has brought up the processes that were previously running on the failed node.

Figure 27-4 and the accompanying text exemplify this process on two hypothetical nodes, Node A and Node B.

Figure 27-4 Example of Failover in a Rack-Mounted Environment

Text description of the illustration oidag101.gif

As the example in Figure 27-4 shows, the failover process in a rack-mounted environment follows this process:

1. Every 10 seconds, the OID Monitor on Node A reports that it is running by sending a message to the database.

2. The OID Monitor on Node B polls the database to learn which, if any, of the other nodes may have failed.

3. When OID Monitor on Node B learns that Node A has not responded for 250 seconds, it regards Node A as having failed. It then retrieves from the database the necessary information about the Oracle Internet Directory servers that were running on Node A. In this example, it learns that the directory replication server had been running on Node A.

4. Because a directory replication server was not already running on Node B, the OID Monitor on Node B starts a directory replication server that corresponds to the directory replication server previously running on Node A.

   See Also: "Oracle Internet Directory Architecture" for information about directory server nodes, directory server instances, and the kinds of directory metadata stored in the database