Oracle Failover options tips Server Tips by Burleson Consulting December 24, 2003

There are four levels of failover technology within the Oracle software.  Each failover option has it's own costs, advantages and disadvantages.

• Oracle9i RAC - This is the most power and complex of the failover solutions and offers continuous availability using Transparent Application Failover (TAF).  Click here to learn how RAC achieves fast failover. Oracle9i Real Application Clusters is an extra-cost option.  The RAC prices are listed in the link below.

E-Business Global Price List Software Investment Guide

• Oracle Streams - This is a high-speed replication solution that takes SQL directly from the log_buffer RAM area and replicates transactions to a remote database.  During a server crash, transactions can be quickly redirected to the replicated system.
   

• Oracle DataGuard - This is a free option with Oracle Enterprise Edition and provides for a automated standby database.  Upon server failure, a series of database procedures synchronizes the standby database and opens it to accept connections. Oracle DataGuard is free with Enterprise Edition.
   

• Oracle Standby Database - This is not an Oracle product, and it is a procedure used prior to Oracle Data Guard to create a standby database.  Oracle7 introduced mechanisms that allow a standby database to be constantly in recovery mode and to be refreshed from Oracle’s archived redo logs. In case of failure, the last redo log could be added to the standby database, and the database could be started in just a few minutes.

Note: Oracle standby servers need to be fully licensed if they are “hot standby” servers that can be used for queries.  Cold standby servers used less than 10 days per year do not need to be licensed.

Also see these related notes on Oracle failover:

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