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Series1 - DISTRIBUTED SYSTEMS Department of Computing...

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Distributed Systems - D N Ranasinghe 1 DISTRIBUTED SYSTEMS Department of Computing Science Umea University
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Distributed Systems - D N Ranasinghe 2 Fundamental Concepts
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Distributed Systems - D N Ranasinghe 3 About Distributed Computing devising algorithms for a set of processes that seek to achieve some form of a ‘cooperative goal’ quoting Leslie Lamport: ‘ a distributed system is one in which the failure of a computer you did not even now existed can render your own computer unusable’
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Distributed Systems - D N Ranasinghe 4 Distributed Algorithm has no shared global information: only decides on local state and the messages they receive has no shared global time frame: observes progress of computation through at best a partial order of events non deterministic behaviour: cannot predict the exact sequence of global states from the study of the algorithm
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Distributed Systems - D N Ranasinghe 5 Design challenges from a systems perspective heterogeneity: in hardware, OS, mode of interaction (c-s, p2p etc), middleware provisioning for developers security: involves eavesdropping, deliberate corruption, process compromise, denial of service etc., scalability: robustness, performance bottlenecks process failures: detecting/suspecting, masking, tolerating, recovery, redundancy in the presence of partial processes failure concurrency
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Distributed Systems - D N Ranasinghe 6 transparency: access (local and remote resources accessed through identical operations) location (resources access independent of physical location) concurrency (process concurrency on shared resources) replication (maintaining replicas with consistency) failure (concealment of failures) mobility (movement of resources and clients)
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Distributed Systems - D N Ranasinghe 7 Role of middleware software layer with services provided to the applications designer consisting of processes and objects mechanisms: Remote Method Invocation object brokering Service Oriented Architecture event notification distributed shared memory…
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Distributed Systems - D N Ranasinghe 8 Motivating application domains information dissemination ( publish-subscribe paradigm): by event registration and notification with time-space decoupling property, based on reliable broadcast and agreement abstractions process control in automation, in industrial systems etc., where consensus may have to be reached on multitude of sensorial inputs cooperative work: multi-user cooperation in editing etc., based on shared persistent space paradigm employing ordered broadcast abstractions distributed databases: need for atomic commitment abstraction on acceptance or rejection of serialized transactions
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Distributed Systems - D N Ranasinghe 9 Motivating application domains software based fault tolerance through replication: uses the so called state machine replication paradigm when a centralized server is required to be made highly available by executing several copies of it whose consistency is guaranteed by total order broadcast abstraction
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