10.5 Conclusion

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In this chapter, we discussed the various high-availability features in a clustered database solution such as RAC. Apart from the basic failover option provided by the clustered operating system, RAC provides some additional advanced features like TAF where the user sessions are migrated to another available instance and data is continuously provided. This failover without interruption to the user's original request happens behind the scene and is transparent to the user. We discussed how this feature could be implemented using the tnsnames-based configuration and how program- matically such a feature could be implemented using OCI APIs.

After the discussions on high availability we also discussed the scalabi lity features of RAC. Multinode configuration of this clustered database provides availability because if one node fails, another node could support the user's requests. Similarly, in an active/active configuration, users could access the common shared database from any of the available nodes or instances. Another important feature provided by RAC is the plug-and- play option, where a node could be added to the cluster configuration dynamically; or when a node of the cluster is dropped, RAC continues to function by dynamically reconfiguring the resources amongst the available instances.

In this chapter we discussed the architecture, configuration, and operation of the RACG. RACG's ideal configuration is a two-node configuration, where one node is configured as the primary node and the second node is configured as the secondary node. While RACG is an enhancement to the failsafe feature available in the previous versions of Oracle, the requirement to have RAC makes this an expensive solution.

A detailed discussion regarding RACG can be found in the Oracle RAC documentation.^[2]

In the next chapter, we will discuss the migration process; for example, the migration process for moving from a single instance configuration to a RAC configuration. Similarly, migrating from an OPS configuration to a RAC will also be discussed.

^[2] ''Oracle Real Application Cluster Guard_Concepts and Administration.''

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