Bully algorithm
In distributed computing, the bully algorithm is a method for dynamically electing a coordinator or leader from a group of distributed computer processes. The process with the highest process ID number from amongst the non-failed processes is selected as the coordinator. Assumptions. The algorithm assumes that: Algorithm. The algorithm uses the following message types: When a process recovers from failure, or the failure detector indicates that the current coordinator has failed, performs the following actions: Analysis. Safety. The safety property expected of leader election protocols is that every non-faulty process either elects a process , or elects  none at all. Note that all processes that elect a leader must decide on the same process as the leader. The Bully algorithm satisfies this property (under the system model specified), and at no point in time is it possible for two processes in the group to have a conflicting view of who the leader is, except during an election. This is true because if it weren't, there are two processes and such that both sent the Coordinator (victory) message to the group. This means and must also have sent each other victory messages. But this cannot happen , since before sending the victory message, Election messages would have been exchanged between the two, and the process with a lower process ID among the two would never send out victory messages. We have a contradiction, and hence our initial assumption that there are two leaders in the system at any given time is false, and that shows that the bully algorithm is safe. Liveness. Liveness is also guaranteed in the synchronous, crash-recovery model. Consider the would-be leader failing after sending an Answer (Alive) message but before sending a Coordinator (victory) message. If it does not recover before  the set timeout on lower ID processes, one of them will become leader eventually (even if some of the other processes crash). If the failed process recovers in time, it simply sends a Coordinator (victory) message to all of the group. Network bandwidth utilization. Assuming that the bully algorithm messages are of a fixed (known, invariant) sizes, the most number of messages are exchanged in the group when the process with the lowest ID initiates an election. This process sends (N−1) Election messages, the next higher ID sends (N−2) messages, and so on, resulting in formula_1 election messages. There are  also the formula_1 Alive messages, and formula_3 co-ordinator messages, thus making the overall number messages exchanged in the worst case be formula_1. External links.