Memcachedb replication feature is based on Berkeley DB's replication api and 
allow you to do a single writing and multiple reading to achieve your HA.

Following private commands is dedicated to replication:

rep_ismaster  -- for two sites replication, and know if it is a master

Command format:

rep_ismaster\r\n

The response line to this command can be one of:

- "REP_TRUE\r\n" to indicate that the deamon is a master.
- "REP_FALSE\r\n" to indicate that the the daemon is not a master.
- "REP_DISABLE\r\n" to indicate that replication is disabled.
- "REP_UNKNOWN\r\n" to indicate that it can not be determinated.

rep_whoismaster -- for two or more sites replication to know who is master

Command format:

rep_whoismaster\r\n

The response line to this command can be one of:

- "<IP>:<PORT>\r\n" to indicate a master's replication host and port.
- "REP_DISABLE\r\n" to indicate that replication is disabled.
- "REP_UNKNOWN\r\n" to indicate that it can not be determinated.

rep_get_priority -- returns the database environment priority.

Command format:

rep_get_priority\r\n

The response line to this command can be one of:

- "<NUM>\r\n"
- "REP_DISABLE\r\n" to indicate that replication is disabled.

rep_set_priority -- specifies the database environment's priority in replication group elections. The priority must be a positive integer, or 0 if this environment cannot be a replication group master.

Command format:

rep_set_priority <NUM>\r\n

The response line to this command can be one of:

- "<NUM>\r\n"
- "REP_DISABLE\r\n" to indicate that replication is disabled.

rep_set_ack_policy -- specifies ack policy of replication. The <NUM> must be a positive integer, and be one of following mapping table.

rep_set_ack_policy <NUM>\r\n

The response line to this command can be one of:

- "<NUM>\r\n"
- "REP_DISABLE\r\n" to indicate that replication is disabled.

Mapping Table:
DB_REPMGR_ACKS_ALL              1
DB_REPMGR_ACKS_ALL_PEERS        2
DB_REPMGR_ACKS_NONE             3
DB_REPMGR_ACKS_ONE              4
DB_REPMGR_ACKS_ONE_PEER         5
DB_REPMGR_ACKS_QUORUM           6

rep_set_ack_timeout -- specifies timeout of waiting a ack. The <NUM> must be a positive integer, and with a max of u_int32_t.

rep_set_ack_timeout <NUM>\r\n

The response line to this command can be one of:

- "<NUM>\r\n"
- "REP_DISABLE\r\n" to indicate that replication is disabled.

rep_set_bulk -- The replication master sends groups of records to the clients in a single network transfer if on. The <NUM> must be 0 or 1, if <NUM> is 0, bulk transfer is off, otherwise on.

rep_set_bulk <NUM>\r\n

The response line to this command can be one of:

- "<NUM>\r\n"
- "REP_DISABLE\r\n" to indicate that replication is disabled.

rep_set_request -- sets the minimum and maximum number of missing log records that a client waits before requesting retransmission.

rep_set_request <MIN> <MAX>\r\n

The response line to this command can be one of:

- "<MIN>/<MAX>\r\n"
- "REP_DISABLE\r\n" to indicate that replication is disabled.

More info about replication, please see "Getting Started with Replication" in 
Berkeley DB's docs. For simplely getting started, see INSTALL file in the distribution.