Oracle Data Guard can operate
in 3 different modes:
o
Maximum
Protection: Transactions are not
allowed to commit until all redo data are written to the online redo logs and
propagated to at least one synchronized secondary database. If for any reason,
the primary database cannot propagate its redo stream to one secondary database,
the primary will shutdown to ensure maximum protection mode.
o
Maximum
Performance: Transactions are not
allowed to commit as soon as the redo are written to the online redo logs. The
redo stream is asynchronously propagated to the secondary databases to ensure
maximum performance mode.
o
Maximum
Availability: Transactions are not
allowed to commit until all redo data are written to the online redo logs and
propagated to at least one synchronized secondary database. If for any reason,
the primary database cannot propagate its redo stream to one secondary
database, the primary will NOT shutdown and operates as it it were in maximum
performance mode until issues are fixed.
Summary
o
Role transition: Changing the role of each database component from
primary database to the secondary database or from secondary database to the
primary database.
o
Switchover: Planned role transition for testing. Manual
intervention.
o
Fail Over: Unplanned failure. Manual or Automatic
intervention. Automatic role transition is the recommended.
o
Primary database: Where the users are connected to access to the
database.
o
Standby database: Exists in the the disaster recovery (DR) site.
Where the users are connected in the case of planned role transition
(Switchover) or in the case of unplanned failure (Fail Over).
o
Data Guard
Observer: Process monitors both
primary and standby databases and performs an automatic fail over when
necessary.
o
The Broker: The management framework for Oracle Data Guard. It
comes integrated into the oracle database enterprise edition.
Fast Start Fail
Over (FSFO): Automatic fail over to the
standby database occurs in case of failure. FSFO requires the broker
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