Recovering a Failed Master

If the primary master fails, log replication stops. Use the gpstate -f command to check the state of standby replication. Use gpactivatestandby to activate the standby master. Upon activation of the standby master, Greenplum Database reconstructs the master host state at the time of the last successfully committed transaction.

To activate the standby master

Ensure a standby master host is configured for the system. See Enabling Master Mirroring.
Run the gpactivatestandby utility from the standby master host you are activating. For example:
```
$ gpactivatestandby -d /data/master/gpseg-1
```
Where -d specifies the data directory of the master host you are activating.

After you activate the standby, it becomes the active or primary master for your Greenplum Database array.
After the utility finishes, run gpstate to check the status:
```
$ gpstate -f
```
The newly activated master's status should be Active. If you configured a new standby host, its status is Passive. When a standby master is not configured, the command displays -No entries found and the message indicates that a standby master instance is not configured.
Optional: If you did not specify a new standby host when running the gpactivatestandby utility, use gpinitstandby to configure a new standby master at a later time. Run gpinitstandby on your active master host. For example:
```
$ gpinitstandby -s <new_standby_master_hostname>
```

Restoring Master Mirroring After a Recovery

Parent topic: Enabling High Availability and Data Consistency Features