#include <db_cxx.h>

int
DbEnv::rep_elect(int nsites, int nvotes,
    int priority, u_int32_t timeout, int *envid, u_int32_t flags);

Description: DbEnv::rep_elect

The DbEnv::rep_elect method holds an election for the master of a replication group.

If the election is successful, 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 DbEnv::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.

Parameters

envid

The envid parameter references memory into which the newly elected master's ID is copied.

nsites

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.

nvotes

The nvotes parameter indicates the number of votes required by the application to successfully elect a new master. It must be a positive integer, no greater than nsites, or 0 if the election should use a simple majority of the nsites value as the requirement. A warning is given if half or fewer votes are required to win an election as that can potentially lead to multiple masters in the face of a network partition.

priority

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).

timeout

The timeout parameter specifies a timeout period for an election. If the election has not completed after timeout microseconds, the election will fail.

flags

The flags parameter is currently unused, and must be set to 0.

Errors

The DbEnv::rep_elect method may fail and throw DbException, encapsulating one of the following non-zero errors, or return one of the following non-zero errors:

DB_REP_UNAVAIL

The replication group was unable to elect a master, or was unable to complete the election in the specified timeout period.

Class

See Also