Bully algorithm

The bully algorithm is a method in distributed computing for dynamically selecting a coordinator by process ID number.

When a process P determines that the current coordinator is down because of message timeouts or failure of the coordinator to initiate a handshake, it performs the following sequence of actions:

# P broadcasts an election message (inquiry) to all other processes with higher process IDs.
# If P hears from no process with a higher process ID than it, it wins the election and broadcasts victory.
# If P hears from a process with a higher ID, P waits a certain amount of time for that process to broadcast itself as the leader. If it does not receive this message in time, it re-broadcasts the election message.

Note that if P receives a victory message from a process with a lower ID number, it immediately initiates a new election. This is how the algorithm gets its name - a process with a higher ID number will bully a lower ID process out of the coordinator position as soon as it comes online.

References

* Witchel, Emmett (2005). [http://www.cs.utexas.edu/users/witchel/372/lectures/25.DistributedCoordination.ppt "Distributed Coordination"] . Retrieved May 4, 2005.