JoshuaEberhart-DistributedSnapshots

# JoshuaEberhart-DistributedSnapshots - Distributed Snapshots...

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Click to edit Master subtitle style Distributed Snapshots: Determining Global States of Distributed Systems Joshua Eberhardt Research Paper: Kanianthra Mani Chandy and Leslie Lamport

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Background n What is a distributed system? n Set of autonomous computers n Communication network n Software that integrates it into a single entity
Figure 1

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Overview n Introduction n Model of a Distributed System n Global-state Detection Algorithm n Motivation n Termination n Stability Detection
Overview n Introduction n Model of a Distributed System n Global-state Detection Algorithm n Motivation n Termination n Stability Detection

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Processes in Distributed Systems n Process is an instance of a computer program being executed. n Processes in a distributed system communicate by sending and receiving messages. n A process can record its own state and the message it sends and receives.
Global States and Processes n To determine a global state, a process p must cooperate with other processes to record their own states and send them to p. n Main problem is to devise an algorithm to record global states.

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Global State Detection Problems n Let y , be a predicate function defined over the global states of the a distributed system D . n (In other words, y (S) is true or false for a global state S of D) n The predicate y is a stable property of D if y ( S ) implies y ( S’ ) for global states S’ of D reachable from S of D
Going Further n Many distributed system problems can be formulated as the general problem of creating an algorithm by which a process in a distributed system can determine whether a stable property y holds. n Examples n Deadlock Detection n Termination Detection

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Structure of Distributed Algorithms n Structured as sequence of phases. n Transient Part n Stable Part n Stability needs to be detected so that one phase can be terminated and another initiated. n Termination of a Computational Phase vs. Termination of a Computation
Termination Phase n The overall problem can be partitioned into the problems of detecting the termination of one phase and initiating a new phase. n Example of a stable property n The k th computational phase has terminated where k = 1, 2, 3, … n Thus we can determine the termination of the kth phase for any given k.

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Overview n Introduction n Model of a Distributed System n Global-state Detection Algorithm n Motivation n Termination n Properties n Stability Detection
n A distributed system consists of a finite set of processes and a finite set of channels . n

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JoshuaEberhart-DistributedSnapshots - Distributed Snapshots...

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