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Oracle10g Grid Computing with RAC
Chapter 3 - High Performance and Highly Available
Database Clusters

Oracle Database Service in HA Cluster

  • Multiple Instances exist at the same time accessing a single database. (Data files are common to the multiple instances).

  • Multiple nodes have read/write access to the shared storage at the same time. Data blocks are read and updated by multiple nodes.

  • Should a failure occur in a node and the oracle instance is not usable or has crashed, the surviving node performs recovery for the crashed instance. There is no need to restart the instance on the surviving node, a parallel instance is already running there.

  • All the client connections continue to access the database through the surviving node/instance. With the help TAF (Transparent Application Failover) facility, clients will be able to move over to the surviving instance near instantaneously.

  • There is no such thing as the moving of Volumes and File system to the surviving node.

Issues with FO Clusters – Hidden Risks

No doubt, there is wide acceptance of failover clusters, and in most situations, FO clusters provide an excellent failover mechanism, but there are some hidden risks with the nature and implementation of FO clusters. 

The hidden risks with FO clusters are as follows:

  • Database Failover is a time consuming process. It is usually a cold a fail-over (Active/passive). A fresh database instance starts on the surviving node. For example, the un-mounting of a file system may hang and as a result, off-line activity may take longer time.

  • The entire process of monitoring and failover depends on scripts. Scripts can become problematic with bugs and sometimes they may not take care of all situations.

  • Cluster technology cannot protect against software corruption and human-induced failures. If the server operating system crashes in such a manner that it corrupts the file system, recovery by the other member of a cluster may not be possible.

  • If the owner of a file accidentally deletes it from the file system, the cluster will be unable to recover the file. Even after failing over to second node, the same problem of file loss exists.

For more information, see the book Oracle 11g Grid and Real Application Clusters 30% off if you buy it directly from Rampant TechPress . 

Written by top Oracle experts, this RAC book has a complete online code depot with ready to use RAC scripts.

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Burleson Oracle Consulting offers Senior Oracle consultants which are available for all areas of Oracle support.  Common Oracle consulting support activities include short-term Oracle tuning, Oracle database troubleshooting, Oracle9i and Oracle10g migration, Oracle9iAS App Server consulting, Oracle design reviews and Oracle requirements evaluation support. Oracle support and Oracle consulting services are priced by the hour, so you only pay for what you need. These one-time Oracle consulting services commonly include:

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  • Repairing down production Oracle database systems

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