In the Bully algorithm, a recovering process starts an election and will become the new coordinator if it has a higher identifier than the current incumbent. Is this a necessary feature of the algorithm?

Question

What will be an ideal response?

Answer 1

First note that this is an undesirable feature if there is no advantage to using a higher-numbered process: the re-election is wasteful. However, the numbering of processes may reflect their relative advantage (for example, with higher-numbered processes executing at faster machines). In this case, the advantage may be worth the re-election costs. Re-election costs include the message rounds needed to implement the election; they also may include application-specific state transfer from the old coordinator to the new coordinator.
To avoid a re-election, a recovering process could merely send a requestStatus message to successive lower- numbered processes to discover whether another process is already elected, and elect itself only if it receives a negative response. Thereafter, the algorithm can operate as before: if the newly-recovered process discovers
the coordinator to have failed, or if it receives an election message, it sends a coordinator message to the remaining processes.