chapter11 - Chapter 11: Coordination and Agreement...

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Introduction Distributed mutual exclusion Elections Multicast communication Consensus and related problems Summary Chapter 11: Coordination and Agreement
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Collaboration behaviors in DS Mutual exclusion Election Multicast Basic, reliable, order Agreement between processes Consensus, byzantine agreement Failure assumptions No failures Benign failures Arbitrary failures Introduction
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The real situation of the Internet Network partition Asymmetric routing Intransitive connectivity Channel assumption: reliable Failed link will be repaired or circumvented Process assumption crash failure without mention, otherwise arbitrary failure Correct process: no crash failure and arbitrary failure Failure assumptions
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Unreliable failure detector Inaccurate unsuspected or suspected Reliable failure detector Inaccurate Unsuspected Failed : detect process crash Require the system is synchronous Implement an unreliable failure detector Each process announce its liveness every T seconds Detector suspects a process if it has not receive the periodic message for D seconds Failure detectors
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Introduction Distributed mutual exclusion Elections Multicast communication Consensus and related problems Summary Chapter 11: Coordination and Agreement
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Assumption Asynchronous, no process fail, reliable channel Application level protocol enter () resourceAccesses () exit () Algorithms for mutual exclusion
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Essential requirements for mutual exlcusion Safety At most one process may execute in the critical section at a time Liveness Requests to enter and exit the critical section(CS) eventually succeed Free from deadlock and starvation Ordering If one request to enter the CS happened-before another, then entry to the CS is granted in that order Algorithms for mutual exclusion
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Evaluate the performance of the algorithms Bandwidth consumed The number of messages sent in each entry and exit operation Client Delay Incurred by a process at each entry and exit operations Throughput Synchronization delay : delay between one process exiting the critical section and the next process entering it Algorithms for mutual exclusion … continued
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Architecture Meet safety and liveness , but not ordering Performance Bandwidth consumption Enter(): A request message, a grant message Exit(): a release message Client Delay (no waiting processes) Request message + grant message Synchronization delay A release message + a grant message The Central server algorithm
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Architecture Meet safety and liveness , but not ordering Performance Bandwidth consumed Continuously consume network bandwidth Client Delay Min : 0 message, when it has just received the token Max : N messages, when it has just passed on the token Synchronization delay Min
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chapter11 - Chapter 11: Coordination and Agreement...

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