Oracle9i Real Application Clusters Concepts
Release 1 (9.0.1)

Part Number A89867-02
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12
Oracle Real Application Clusters Guard Operation

This chapter describes the operation of Oracle Real Application Clusters Guard. It contains the following sections:

Overview of Oracle Real Application Clusters Guard Operation

This chapter describes the operation of Oracle Real Application Clusters Guard. It is important to distinguish between the automatic actions of Oracle Real Application Clusters Guard and the actions that the user can take when Oracle Real Application Clusters Guard prompts the user. The most typical case is what happens when the primary instance fails, and it illustrates the automatic actions of Oracle Real Application Clusters Guard as well as the control that the user has over the final outcome.

See Also:

Oracle Real Application Clusters Guard Administration and Reference Guide for detailed information about using PFSCTL commands 

Failure of the Primary Instance

Figure 12-1 shows what happens when the primary instance fails. During normal operation, both Node A and Node B are operational. Pack A is running on its home node, Node A, and has the primary instance role. It contains the primary instance and an IP address. Pack B is running on its home node, Node B, and has the secondary instance role. It contains the secondary instance and an IP address.

Figure 12-1 Failure of the Primary Instance


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If the primary instance fails, then Oracle Real Application Clusters Guard automatically does the following:

Now both Pack A and Pack B are running on Node B. Pack B contains the primary instance and its IP address. Pack A contains only an IP address. Nothing is running on Node A.

A notification about the failure is sent to the PFS log. If the user has customized the Oracle Real Application Clusters Guard call-home script to notify an administrator of the failure, then the administrator can use the RESTORE command to restore the secondary instance role. Oracle Real Application Clusters Guard starts Pack A on Node A. Because the instance on Node B now has the primary instance role, the instance associated with Pack A assumes the secondary instance role when it restarts. When both instances are up and operating, the system has resilience.

See Also:

Oracle9i Real Application Clusters Administration for detailed information about using PFSCTL commands and more information about how the call-home feature works in Oracle Real Application Clusters Guard 

Restoring the Nodes to their Original Roles

After Oracle Real Application Clusters Guard fails over the primary instance role and the user restores the secondary instance role, the system is resilient and the Packs are on their home nodes, but the instance roles are reversed. If you want the primary instance to run on the preferred primary node, then you must use the MOVE_PRIMARY and RESTORE commands. Figure 12-2 shows what happens when you return the roles to their preferred nodes.

Figure 12-2 Returning the Packs to Their Home Nodes


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Pack A is on Node A and has the secondary instance role. Pack B is on Node B and has the primary instance role. When the user enters the MOVE_PRIMARY command, Oracle Real Application Clusters Guard halts Pack B, making the secondary instance, which is running on Node A, becomes the primary instance.

When the user enters the RESTORE command, Oracle Real Application Clusters Guard starts Pack B on Node B. Pack B assumes the secondary instance role.

The packs are now running on their home nodes with their original roles.

Failure of the Secondary Instance

Figure 12-3 shows what happens when the secondary instance fails.

Figure 12-3 Failure of the Secondary Instance


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When the secondary instance fails, Oracle Real Application Clusters Guard sends a notification of the failure to the PFS log. The user must enter the RESTORE command to restore the secondary instance role to Node B. Both packs retain their original roles on their home nodes.


Note:

When there is any failure in the system, it is important to analyze the cause and repair the problem, as well as to restore resilience. For information about troubleshooting, refer to Oracle9i Real Application Clusters Deployment and Performance. 


Failure of Both Instances

Figure 12-4 shows what happens when both instances fail.

Figure 12-4 Failure of Both Instances


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Initially, Pack A is on Node A and has the primary instance role. Pack B is on Node B and has the secondary instance role. If the primary instance fails, then the secondary instance assumes the primary instance role and Pack A starts on Node B with only its IP address active.

If the other instance fails and cannot be restarted, then Pack A remains on Node B and Pack B is started on Node A. Because both packs are on their foreign nodes, only their IP addresses are activated. No instances are running.

Because the Packs are still up, the user must halt them with the PFSHALT command. If the user tries to start the instances with the PFSBOOT command before halting the packs, then the PFSBOOT command will fail.

See Also:

Oracle Real Application Clusters Guard Administration and Reference Guide for information about how to use PFSCTL commands 


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