A13_Elections - Election Algorithms and Distributed...

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Election Algorithms and Distributed Processing Section 6.5
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Outline Election algorithms – introduction Traditional election algorithms Bully algorithm Ring algorithm Wireless election algorithms
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Need for a Coordinator Many algorithms used in distributed systems require a coordinator For example, see the centralized mutual exclusion algorithm. In general, all processes in the distributed system are equally suitable for the role Election algorithms are designed to choose a coordinator.
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Election Algorithms Any process can serve as coordinator Any process can “call an election” (initiate the algorithm to choose a new coordinator). There is no harm (other than extra message traffic) in having multiple concurrent elections. Elections may be needed when the system is initialized, or if the coordinator crashes or retires.
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Assumptions Every process/site has a unique ID; e.g. the network address a process number Every process in the system should know the values in the set of ID numbers, although not which processors are up or down. The process with the highest ID number will be the new coordinator. Process groups (as with ISIS toolkit or MPI) satisfy these requirements.
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Requirements When the election algorithm terminates a single process has been selected and every process knows its identity. • Formalize: every process p i has a variable e i to hold the coordinator’s process number. i, e i = undefined or e i = P, where P is the non-crashed process with highest id All processes (that have not crashed) eventually set e i = P.
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The Bully Algorithm - Overview Process
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This note was uploaded on 12/14/2011 for the course CS 690 taught by Professor Staff during the Fall '11 term at University of Alabama - Huntsville.

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A13_Elections - Election Algorithms and Distributed...

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