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Leader Election

Leader Election. Breaking the symmetry in a system. Ring based leader election. The network is known to be a ring Ring size is unknown. Chang-Robert’s algorithm. Every process sends an election message with its id to the left process if it has not seen a message from a higher process

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Leader Election

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  1. Leader Election Breaking the symmetry in a system

  2. Ring based leader election • The network is known to be a ring • Ring size is unknown

  3. Chang-Robert’s algorithm • Every process sends an election message with its id to the left process if it has not seen a message from a higher process • Forward any message with an id greater than own id to the left • If a process receives its own election message it is the leader • It then declares itself to be the leader by sending a leader message

  4. Chang Roberts Leader Election • Worst case message complexity Best case Worst case

  5. Hirschberg-Sinclair algorithm • Assume ring is bidirectional • Carry out elections on increasingly larger sets • Algorithm works in asynchronous rounds • Only processes that win the election in round r can proceed to round r+1 • Algorithm: Pi is the leader in round r iff it has the largest id of all nodes that are at a distance 2r or less from Pi

  6. Hirschberg-Sinclair algorithm • Initially: • All processes are leaders • Round 0: • 6 , 7 and 8 are leaders • Round 1: • 7, 8 are leaders • Round 2: • 8 is the only leader • At most log(N) rounds

  7. Election on general graphs • Totally connected graph – all nodes are mutually connected • Homework assignment: • Give a randomized algorithm to elect a leader • Analyze its message and time complexity

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