Berkeley DB Reference Guide: Replication environment priorities

Berkeley DB Reference Guide:
Berkeley DB Replication

Replication environment priorities

Each database environment included in a replication group must have a priority, which specifies a relative ordering among the different environments in a replication group. This ordering is a factor in determining which environment will be selected as a new master in case the existing master fails. Both Replication Manager applications and applications which use the Base replication API should specify environment priorities.

Priorities are an unsigned integer, but do not need to be unique throughout the replication group. A priority of 0 means the system can never become a master, regardless. Otherwise, larger valued priorities indicate a more desirable master. For example, if a replication group consists of three database environments, two of which are connected by an OC3 and the third of which is connected by a T1, the third database environment should be assigned a priority value which is lower than either of the other two.

Desirability of the master is first determined by the client having the most recent log records. Ties in log records are broken with the client priority. If both sites have the same number of log records and the same priority, one is selected at random.