Logical standby database
Oracle Data Guard also offers a logical standby database capability. With this capability,
the standard Oracle archive logs are transformed into SQL transactions, and
these are applied to an open standby database. The logical standby database is different
physically from the primary standby database and can be used for different tasks.
For example, the primary database might be indexed for transaction processing while
the standby database might be indexed for data warehousing. Although physically
different from the primary database, the secondary database is logically the same and
can take over processing in case the primary fails. As archive logs are shipped from
the primary to the secondary, undo records in the shipped archive log can be compared
to the logical standby undo records to guard against potential corruption. As
of Oracle Database 10g, youcan instantiate the logical standby database without
quiescing the primary.
Figure 11-10. Standby database
??? Production database is copied
to the standby system
??? Standby system is started in
standby recovery mode
??? As archived redo logs are
generated on the production
systems, they are transferred to
the standby system and applied
??? If the production system fails,
the standby system is activated
Production
System
(New York)
Standby
System
(London)
Database Database
Copy
Archived
Redo Logs
Oracle
Instance
Oracle
Instance
284 | Chapter 11: Oracle and High Availability
Oracle Data Guard management
The Oracle Data Guard broker provides monitoring and control for physical and logical
standby databases and components.
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