How to Change Apply Instance in Oracle Data Guard RAC Standby Using DGMGRL

 

If you're running Oracle Data Guard in a RAC (Real Application Clusters) environment, you likely have a standby database with multiple instances. In such a setup, only one instance is responsible for applying redo logs — this is called the apply instance.

Sometimes, you may need to change the apply instance — for example, due to load balancing, maintenance, or an ORA-16789: standby apply not running error.

Let's see how to change the apply instance in Data Guard using dgmgrl, the Oracle Data Guard Broker command-line tool.

What is the Apply Instance in Oracle Data Guard?

 In Oracle Data Guard, the Apply Instance refers to the instance responsible for applying redo logs to the standby database. This process ensures that the standby database remains synchronized with the primary database by continuously applying changes recorded in the redo logs.

Let's see the current configuration.

DGMGRL> show configuration

Configuration - broker_config

  Protection Mode: MaxPerformance
  Databases:
    ORCL    - Primary database
    ORCLSBY - Physical standby database

Fast-Start Failover: DISABLED

Configuration Status:
SUCCESS

 Check Current Apply Instance

DGMGRL> show database 'ORCLSBY'

Database - ORCLSBY

  Role:            PHYSICAL STANDBY
  Intended State:  APPLY-ON
  Transport Lag:   0 seconds
  Apply Lag:       0 seconds
  Real Time Query: ON
  Instance(s):
    ORCLSBY1
    ORCLSBY2 (apply instance)

Database Status:
SUCCESS

Current apply instance is ORCLSBY2 as seen above. To change it to ORCLSBY1 disable apply temporarily, set a new apply Instance and enable apply again

DGMGRL> edit database 'ORCLSBY' set state='apply-off';
Succeeded.
DGMGRL> show database 'ORCLSBY'

Database - ORCLSBY

  Role:            PHYSICAL STANDBY
  Intended State:  APPLY-OFF
  Transport Lag:   0 seconds
  Apply Lag:       0 seconds
  Real Time Query: OFF
  Instance(s):
    ORCLSBY
    OCRLSBY (apply instance)

Database Status:
SUCCESS

DGMGRL> edit database 'ORCLSBY' set state='apply-on' with apply instance ='ORCLSBY1';
Succeeded.

Lets verify the configuration now.

DGMGRL> show database 'ORCLSBY'

Database - ORCLSBY

  Role:            PHYSICAL STANDBY
  Intended State:  APPLY-ON
  Transport Lag:   0 seconds
  Apply Lag:       0 seconds
  Real Time Query: ON
  Instance(s):
    ORCLSBY1 (apply instance)
    ORCLSBY2

Database Status:
SUCCESS

DGMGRL> show configuration

Configuration - broker_config

  Protection Mode: MaxPerformance
  Databases:
    ORCL    - Primary database
    ORCLSBY - Physical standby database

Fast-Start Failover: DISABLED

Configuration Status:
SUCCESS

Now you'll see Current Apply Instance: ORCLSBY1