DB_ENV->rep_elect(DB_ENV *env, int nsites,
int priority, u_int32_t timeout, int *envid);
The DB_ENV->rep_elect method holds an election for the master of a replication
group, returning the new master's ID in the envid parameter.
The nsites parameter indicates the number of environments that
the application believes are in the replication group. This number is
used by Berkeley DB to avoid having two masters active simultaneously, even
in the case of a network partition. During an election, a new master
cannot be elected unless more than half of nsites agree on
the new master. Thus, in the face of a network partition, the side of
the partition with more than half the environments will elect a new
master and continue, while the environments communicating with fewer
than half the other environments will fail to find a new master.
The priority parameter is the priority of this environment. It
must be a positive integer, or 0 if this environment is not permitted
to become a master (see Replication
environment priorities for more information).
The timeout parameter specifies a timeout period for an
election. If the election has not completed after timeout
microseconds, the thread will return DB_REP_UNAVAIL.
The DB_ENV->rep_elect method either returns successfully, with the new
master's environment ID in the memory pointed to by the envid
parameter, or it will return DB_REP_UNAVAIL if the participating
group members were unable to elect a new master for any reason. In the
event of a successful return, the new master's ID may be the ID of the
previous master, or the ID of the current environment. The application
is responsible for adjusting its usage of the other environments in the
replication group, including directing all database updates to the newly
selected master, in accordance with the results of this election.
The thread of control that calls the DB_ENV->rep_elect method must not be the
thread of control that processes incoming messages; processing the
incoming messages is necessary to successfully complete an election.
The DB_ENV->rep_elect method returns a non-zero error value on failure and 0 on success.
The DB_ENV->rep_elect method may fail and return a non-zero error for the following conditions:
- The replication group was unable to elect a master.
The DB_ENV->rep_elect method may fail and return a non-zero error for errors specified for other Berkeley DB and C library or system functions.
If a catastrophic error has occurred, the DB_ENV->rep_elect method may fail and
in which case all subsequent Berkeley DB calls will fail in the same way.
Replication and Related Methods
Copyright Sleepycat Software