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the Data Guard Broker. The Data Guard Broker provides centralized
management of all resources within a Data Guard configuration. Through its
command line interface (DGMGRL), the Data Guard Broker uses single
commands to perform the equivalent work of multiple SQL*Plus statements,
greatly simplifying the management of a Data Guard configuration. Note that the
Data Guard Broker is included with Data Guard and does not require a separate
installation.
Fast-Start Failover is configured using DGMGRL or Oracle Enterprise Manager
10g Grid Control. Enterprise Manager provides a GUI interface that interacts
with the Data Guard Broker. Not only does this provide a very easy to use
interface for monitoring and control, it also enables centralized management of all
resources in one or more Data Guard configurations.
Using either DGMGRL or Oracle Enterprise Manager, the administrator
configures the three essential participants (figure 1) in a fast-start failover
configuration:
• The primary database
• The target standby database
• The Fast-Start Failover Observer
The target standby database will become the new primary database following a
fast-start failover (note there can be multiple standby databases in a Data Guard
configuration).
The Observer is a separate process incorporated into the DGMGRL client that
continuously monitors the primary database and the target standby database for
possible failure conditions (ref. Fig. 1). The Observer should be run on a different
computer host than that of the primary and target standby databases so that it is
not subject to any failures that affect the primary or standby computer hosts.
The underlying rule of fast-start failover is that out of these three participants,
whichever two can communicate with each other will determine the outcome of
fast-start failover. For example, if the primary database becomes unavailable, the
Observer confirms with the target standby database that the primary database is
unavailable and that the target standby database is synchronized with the primary
database, and if so, initiates a fast-start failover to the target standby database.
Details for configuring & enabling Fast-Start Failover are as follows:
Fast-Start Failover – Oracle Data Guard 10g Release 2 Page 6
• Begin with a Data Guard configuration that includes a primary database
and at least one standby database configured using Maximum Availability
protection mode with LGWR SYNC Redo Transport Services. Flashback
database and Flash Recovery Area must also be enabled on both primary
and standby databases.
• Designate a third system to be the Observer host. It must have the
DGMGRL utility installed and have Oracle Net connectivity to both the
primary and standby. The Observer should run on a host that is not
located in the same datacenter as the primary database, and should be on
a different server than the standby database.
• Data Guard Real Time Apply is also recommended to minimize failover
time. This will insure that the standby database is up-to-date with the
latest redo received from the primary. This eliminates any delay at
failover caused by waiting for the standby database to complete the
application of received redo.
• Configure FastStartFailoverTarget by providing the
DB_UNIQUE_NAME of the database that is intended to be the new
primary.
Primary Site Standby Site
Observer
database database
Figure 1 Fast-Start Failover Configuration
Fast-Start Failover – Oracle Data Guard 10g Release 2 Page 7
DGMGRL > EDIT DATABASE ‘North_Sales’ SET
PROPERTY FastStartFailoverTarget = ‘DR_Sales’;
• Configure the failover threshold which is the number of seconds the
Observer attempts to reconnect to the primary database before initiating a
failover.
DGMGRL> EDIT CONFIGURATION SET PROPERTY
FastStartFailoverThreshold = 45;
• Start
DGMGRL> ENABLE FAST_START FAILOVER;
DGMGRL> START OBSERVER;
Following a fast-start failover, the Observer periodically attempts to contact the
old primary database. If a reconnection to the old primary database is made, the
Observer automatically reinstates the old primary database so that it can be a
standby database to the new primary database. At all times through this process,
Data Guard insures that no new transactions are allowed in the old primary
database prior to assuming a standby role. This quickly restores high availability to
the Data Guard configuration.
EVENTS THAT TRIGGER FAST-START FAILOVER
The following database conditions will trigger a fast-start failover:
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