Managing Far Sync Instances

An Oracle Data Guard far sync instance is a redo transport destination that accepts redo from a primary database and forwards that redo to one or more redo destinations in the configuration.

It is similar to a physical standby database in that it has a control file, receives redo into Standby Redo Log files (SRLs), and archives those SRLs to local Archived Redo Logs (ARLs). But unlike a standby database, a far sync instance does not have data files, cannot be opened, and cannot apply received redo. These limitations yield the benefit of using fewer disk and processing resources. More importantly, a far sync instance provides the ability to failover to a terminal database with no data loss if it receives redo data using synchronous transport mode and the configuration protection mode is set to maximum availability.

Starting with Oracle Database Release 21c, you can use the CREATE FAR_SYNC command to create a new far sync instance and add it to the broker configuration. See CREATE FAR_SYNC.

The following example shows how to add a far sync instance to a broker configuration.

DGMGRL> ADD FAR_SYNC FS1 AS CONNECT IDENTIFIER IS FS1.example.com;
Far Sync FS1 added
DGMGRL> ENABLE FAR_SYNC FS1;
Enabled.
DGMGRL> SHOW CONFIGURATION;
 
Configuration - DRSolution
 
  Protection Mode: MaxPerformance
  Members:
  North_Sales  - Primary database
    FS1        - Far Sync
    South_Sales - Physical standby database
 
Fast-Start Failover: DISABLED
Configuration Status:
SUCCESS

After a far sync instance has been added to the configuration, set up redo transport to support maximum availability and then upgrade the protection mode:

DGMGRL> EDIT DATABASE 'North_Sales' SET PROPERTY 'RedoRoutes' = '(LOCAL : FS1 SYNC)';
DGMGRL> EDIT FAR_SYNC 'FS1' SET PROPERTY 'RedoRoutes' = '(North_Sales : South_Sales ASYNC)';
DGMGRL> EDIT CONFIGURATION SET PROTECTION MODE AS MaxAvailability;
DGMGRL> SHOW CONFIGURATION;
 
Configuration - DRSolution
 
  Protection Mode: MaxAvailability
  Members:
  North_Sales  - Primary database
    FS1          - Far Sync
      South_Sales - Physical standby database
 
Fast-Start Failover: DISABLED
Configuration Status:
SUCCESS

To ensure that maximum availability protection mode can be maintained when South_Sales is the primary database, after a switchover or a failover, add a second far sync instance to the configuration so that South_Sales can send redo in synchronous mode which in turn will send redo to the new terminal database, North_Sales, after the role transition.

The following example shows how to add a second far sync instance to the broker configuration:

DGMGRL> ADD FAR_SYNC FS2 AS CONNECT IDENTIFIER IS FS2.example.com;
Far Sync FS2 added
DGMGRL> EDIT FAR_SYNC 'FS2' SET PROPERTY 'RedoRoutes' = '(South_Sales : North_Sales ASYNC)';
DGMGRL> ENABLE FAR_SYNC FS2;
Enabled.
DGMGRL> EDIT DATABASE 'South_Sales' SET PROPERTY 'RedoRoutes' = '(LOCAL : FS2 SYNC)';
DGMGRL> SHOW CONFIGURATION;
 
Configuration - DRSolution
 
  Protection Mode: MaxAvailability
  Members:
  North_Sales  - Primary database
    FS1          - Far Sync
      South_Sales - Physical standby database
      FS2         - Far Sync (inactive)
 
Fast-Start Failover: DISABLED
Configuration Status:
SUCCESS

If a far sync instance is monitored for availability by Oracle Clusterware (for example, in an Oracle Restart, Oracle Real Application Clusters (Oracle RAC), or Oracle RAC One Node installation), then use the SRVCTL utility to specify a default open mode of mount. You can use a command such as the following:

srvctl modify database -d <db_unique_name> -startoption MOUNT