Chapter4 - Chapter 4: Global State and Snapshot Recording...

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Unformatted text preview: Chapter 4: Global State and Snapshot Recording Algorithms Ajay Kshemkalyani and Mukesh Singhal Distributed Computing: Principles, Algorithms, and Systems Cambridge University Press A. Kshemkalyani and M. Singhal (Distributed Computing) Global State and Snapshot Recording Algorithms CUP 2008 1 / 51 Distributed Computing: Principles, Algorithms, and Systems Introduction Recording the global state of a distributed system on-the-fly is an important paradigm. The lack of globally shared memory, global clock and unpredictable message delays in a distributed system make this problem non-trivial. This chapter first defines consistent global states and discusses issues to be addressed to compute consistent distributed snapshots. Then several algorithms to determine on-the-fly such snapshots are presented for several types of networks. A. Kshemkalyani and M. Singhal (Distributed Computing) Global State and Snapshot Recording Algorithms CUP 2008 2 / 51 Distributed Computing: Principles, Algorithms, and Systems System model The system consists of a collection of n processes p 1 , p 2 , ..., p n that are connected by channels. There are no globally shared memory and physical global clock and processes communicate by passing messages through communication channels. C ij denotes the channel from process p i to process p j and its state is denoted by SC ij . The actions performed by a process are modeled as three types of events: Internal events,the message send event and the message receive event. For a message m ij that is sent by process p i to process p j , let send ( m ij ) and rec ( m ij ) denote its send and receive events. A. Kshemkalyani and M. Singhal (Distributed Computing) Global State and Snapshot Recording Algorithms CUP 2008 3 / 51 Distributed Computing: Principles, Algorithms, and Systems System model At any instant, the state of process p i , denoted by LS i , is a result of the sequence of all the events executed by p i till that instant. For an event e and a process state LS i , e LS i iff e belongs to the sequence of events that have taken process p i to state LS i . For an event e and a process state LS i , e negationslash LS i iff e does not belong to the sequence of events that have taken process p i to state LS i . For a channel C ij , the following set of messages can be defined based on the local states of the processes p i and p j Transit: transit ( LS i , LS j ) = { m ij | send ( m ij ) LS i logicalandtext rec ( m ij ) negationslash LS j } A. Kshemkalyani and M. Singhal (Distributed Computing) Global State and Snapshot Recording Algorithms CUP 2008 4 / 51 Distributed Computing: Principles, Algorithms, and Systems Models of communication Recall, there are three models of communication: FIFO, non-FIFO, and Co....
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This note was uploaded on 02/23/2012 for the course COMP 553 taught by Professor Ajay during the Spring '12 term at Ill. Chicago.

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Chapter4 - Chapter 4: Global State and Snapshot Recording...

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