Oracle has a number of features that contribute to high availability:
Standby database
Oracle can provide database redundancy by maintaining a copy of the primary
database on another machine, usually at another site. Redo logs from the primary
server are shipped to the standby server and applied there to duplicate the
production activity. Oracle8i introduced the automated shipping of redo logs to
the standby site and the ability to open the standby database for read-only access
for reporting.
Oracle9i Release 2 introduced the concept of logical standby. With a logical
standby database the changes are propagated with SQL statements, rather than
redo logs, which allow the logical standby database to be used for other database
operations.
Transparent Application Failover (TAF)
TAF is a programming interface that automatically connects a user session to
another Oracle instance should the primary instance fail. Any queries that were
in process are resumed from the point of the last row fetched for the result set.
218 | Chapter 9: Oracle and Transaction Processing
Oracle Streams/Advanced Queuing (AQ)
AQ in Oracle Streams provides a method for asynchronous, or deferred, intersystem
communication, allowing systems to operate more independently.
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