Managing States of Broker Configuration Members

The members of a configuration can be in various states which, in an enabled configuration, determine the behavior of Oracle Data Guard.

The following table describes the various states.

Note that the following are not listed in the table:

Snapshot standby databases (because they do not have states; they only receive redo data)
Far sync instances (because they do not have states; they only receive redo and forward it to a standby database)
Zero Data Loss Recovery Appliances (because they do not have states)

Table 4-1 Database States and Descriptions

Database Role	State Name	Description
Primary	`TRANSPORT-ON`	Redo transport services are set up to transmit redo data to the standby databases or far sync instances when the primary database is open for read/write access. If this is an Oracle RAC database, all instances open in read/write mode will have redo transport services running. This is the default state for a primary database when it is enabled for the first time.
Primary	`TRANSPORT-OFF`	Redo transport services are stopped on the primary database. If this is an Oracle RAC database, redo transport services are not running on any instances.
Physical standby	`APPLY-ON`	Redo Apply is started on a physical standby database. If the standby database is an Oracle RAC database, the broker starts Redo Apply on exactly one standby instance, called the apply instance. If this instance fails, the broker automatically chooses another instance that is either mounted or open read-only. This new instance then becomes the apply instance. As of Oracle Database 12c Release 2 (12.2.0.1), Redo Apply can be set up to run on each active running physical standby instance. If a database has already been set up to run Redo Apply on multiple instances, then you can use the Data Guard broker property `ApplyInstances` to restrict the number of instances that are involved in Redo Apply on an Oracle RAC physical standby database. `APPLY-ON` is the default state for a physical standby database when it is enabled for the first time. If a license for the Oracle Active Data Guard option has been purchased, a physical standby database can be open while Redo Apply is active. This capability is known as real-time query. See Oracle Data Guard Concepts and Administration for more details.
Physical standby	`APPLY-OFF`	Redo Apply is stopped. If this is an Oracle RAC database, there is no instance running Apply Services until you change the database state to `APPLY-ON`.
Logical standby	`APPLY-ON`	SQL Apply is started on the logical standby database when it is opened and the logical standby database guard is on. If this is an Oracle RAC database, SQL Apply is running on one instance, the apply instance. If this instance fails, the broker automatically chooses another open instance. This new instance becomes the apply instance. This is the default state for a logical standby database when it is enabled for the first time.
Logical standby	`APPLY-OFF`	SQL Apply is stopped. The logical standby database guard is on. If this is an Oracle RAC database, there is no instance running SQL Apply until you change the state to `APPLY-ON`.

Database State Transitions

You can use the DGMGRL EDIT DATABASE command to explicitly change the state of a database.

For example, the EDIT DATABASE command in the following example changes the state of the North_Sales database to TRANSPORT-OFF.

DGMGRL> EDIT DATABASE 'North_Sales' SET STATE='TRANSPORT-OFF';
Succeeded.

The following sections describe in more detail the possible state transitions for primary and standby databases.

Primary Database State Transitions

When transitioning the primary database to the TRANSPORT-ON state, the broker sets up redo transport services using the redo transport-related properties of the configuration members and the RedoRoutes property at the primary database. Redo transport services setup is done by setting the LOG_ARCHIVE_DEST_n and LOG_ARCHIVE_DEST_STATE_n initialization parameters on the primary database, and the LOG_ARCHIVE_CONFIG initialization parameter on all databases (primary or standby) and far sync instances. If necessary, the broker also sets up the data protection mode of the database to match the protection mode recorded in the broker configuration file. Finally, if the database is open, the broker switches a log for each thread to initiate redo transport services.

When transitioning the primary database to the TRANSPORT-OFF state, the broker turns off redo transport services to all broker-managed standbys by resetting the LOG_ARCHIVE_DEST_STATE_n initialization parameter. Transmission of redo data to all broker-managed standbys is stopped. Log files continue to be archived at the primary database.

If the primary database is an Oracle RAC database, the broker configures redo transport services on all primary instances with the same settings.

Physical Standby Database State Transitions

When transitioning a physical standby database to the APPLY-ON state, the broker starts Redo Apply with options specified by the Redo Apply-related properties. If the standby is an Oracle RAC database, then the broker starts Redo Apply on one standby instance, called the apply instance.

Redo Apply can be set up to run on multiple active running physical standby instances. (This feature requires the standby database to have a license for the Oracle Active Data Guard option.) If a database has already been set up to run Redo Apply on multiple instances, then you can use the Data Guard broker property ApplyInstances to restrict the number of instances that are involved in Redo Apply on an Oracle RAC physical standby database.

If a license for the Oracle Active Data Guard option has been purchased, a physical standby database can be open while Redo Apply is active. This capability is known as real-time query. See Oracle Data Guard Concepts and Administration for more details.

The apply instance must be open before starting Redo Apply if any other instance is open.

When transitioning to the APPLY-OFF state, the broker stops Redo Apply.

Note:

If you perform online database relocation with Oracle RAC One Node on a physical standby, then the new instance is started in the same mode as the currently running instance. Therefore, if the database is mounted on the original instance, then the database will be mounted on the new instance. Likewise, if the database is open on the original instance, then the database will be open on the new instance. This may result in the new instance starting in a mode that does not match the start option recorded with Oracle Clusterware for the database.

Logical Standby Database State Transitions

When transitioning a logical standby database to the APPLY-ON state, the broker will wait until the database is open, and then enable the database guard to prevent modifications to tables in the logical standby database, and start SQL Apply with options specified by the log apply-related properties. If the logical standby database is an Oracle RAC database, the broker starts SQL Apply on one standby instance, the apply instance.

When transitioning to the APPLY-OFF state, the broker stops SQL Apply.