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# Leader Election - PowerPoint PPT Presentation

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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Presentation Transcript

Breaking the symmetry in a system

• 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
• 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
• Worst case message complexity

Best case

Worst case

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
Hirschberg-Sinclair algorithm
• Initially: