Enabling Master Mirroring

You can configure a new Greenplum Database system with a standby master using gpinitsystem or enable it later using gpinitstandby. This topic assumes you are adding a standby master to an existing system that was initialized without one.

For information about the utilities gpinitsystem and gpinitstandby, see the Greenplum Database Utility Guide.

To add a standby master to an existing system

Ensure the standby master host is installed and configured: gpadmin system user created, Greenplum Database binaries installed, environment variables set, SSH keys exchanged, and data directory created. Greenplum Database
Run the gpinitstandby utility on the currently active primary master host to add a standby master host to your Greenplum Database system. For example:
```
$ gpinitstandby -s smdw
```
Where -s specifies the standby master host name.
To switch operations to a standby master, see Recovering a Failed Master.

You can display the information in the Greenplum Database system view pg_stat_replication. The view lists information about the walsender process that is used for Greenplum Database master mirroring. For example, this command displays the process ID and state of the walsender process:

$ psql dbname -c 'SELECT procpid, state FROM pg_stat_replication;'

For information about the pg_stat_replication system view, see the Greenplum Database Reference Guide.