Data Guard Architecture
In a Data Guard implementation, a database running in ARCHIVELOG mode is designated as the
primary database for an application. One or more standby databases, accessible via Oracle Net,
provide for failover capabilities. Data Guard automatically transmits redo information to the
standby databases, where it is applied. As a result, the standby database is transactionally consistent.
Depending on how you configure the redo application process, the standby databases may be in
sync with the primary database or may lag behind it. Figure 13-1 shows a standard Data Guard
implementation.
The redo log data is transferred to the Standby Databases via Log Transport Services, as
defined via your initialization parameter settings. Log Apply Services apply the redo information
to the standby databases. A third set of services, Role Management Services, simplify the process
of making Standby Databases serve as the primary database.
O
FIGURE 13-1 Simple Data Guard configuration
Chapter 13: Oracle Data Guard 477
NOTE
The primary database can be a single instance or a multi-instance Real
Application Clusters implementation.
Physical vs. Logical Standby Databases
Two types of standby databases are supported: physical standbys and logical standbys. A physical
standby database has the same structures as the primary database. A logical standby database may
have different internal structures (such as additional indexes used for reporting).
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