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.
- If P gets an election message (inquiry) from another process with a lower ID it sends an "I am alive" message back and starts new elections.
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.
See also
References
- Witchel, Emmett (2005). "Distributed Coordination". Retrieved May 4, 2005.
- Hector Garcia-Molina, Elections in a Distributed Computing System, IEEE Transactions on Computers, Vol. C-31, No. 1, January (1982) 48-59