lect-06 - Computer Science 425 Distributed Systems Lecture...

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2006, 2007, M. T. Harandi Lecture 6-1 Computer Science 425 Distributed Systems Lecture 6 Causality
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2006, 2007, M. T. Harandi Lecture 6-2 Causality Violation P1 P2 P3 1 2 3 4 5 0 0 0 1 2 Physical Time 4 6 Include(obj1 ) obj1.method() P2 has obj1 Causality violation occurs when order of messages causes an action based on information that another host has not yet received. In designing a DS, potential for causality violation is important
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2006, 2007, M. T. Harandi Lecture 6-3 Detecting Causality Violation P1 P2 P3 (1,0,0) (2,0,0) Physical Time (2,0,2) Potential causality violation can be detected by vector timestamps. If the vector timestamp of a message is less than the local vector timestamp, on arrival, there is a potential causality violation. 0,0,0 0,0,0 0,0,0 1,0,0 2,0,1 2,2,2 2,1,2 2,0,2 2,0,0 Violation: (1,0,0) < (2,1,2)
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2006, 2007, M. T. Harandi Lecture 6-4 Communication Modes in DS Unicast ( best effort or reliable ) Messages are sent from exactly one host to one host Best effort guarantees that if a message is delivered it would be intact Reliable guarantees delivery of messages. Broadcast Messages are sent from exactly one host to all hosts on the same network. Reliable broadcast protocols are not practical Multicast Messages are sent from exactly one host to several hosts on the same or different networks. Multicast can be implemented above a reliable unicast
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lect-06 - Computer Science 425 Distributed Systems Lecture...

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