Should the data center fail completely, the last two items??”database redundancy and
data redundancy??”provide for disaster recovery.
Oracle Data Guard: Standby Database for Redundancy
Oracle??™s physical standby database functionality was introduced in Oracle 7.3 to provide
database redundancy. In Oracle9i, this concept was extended to include support
for a logical standby database. The enhanced feature set is called Oracle Data Guard.
The concept of a physical standby database is simple??”keep a copy of the database
files at a second location, ship the redo logs to the second site as they are filled, and
apply them to the copy of the database. This process keeps the standby database ???a
few steps??? behind the primary database. If the primary site fails, the standby database
is opened and becomes the production database. The potential data loss is
limited to the transactions in any redo logs that have not been shipped to the standby
site. Figure 11-10 illustrates the standby database feature.
The physical standby database can be used to offload reporting, such as end-of-day
reports, from the primary server to the standby server.
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