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Logical clocks and logical time
Logical clocks and logical time
Logical clocks and logical time
Logical clocks and logical time
Logical clocks and logical time
Logical clocks and logical time
Logical clocks and logical time
Logical clocks and logical time
Logical clocks and logical time
Logical clocks and logical time
Logical clocks and logical time
Logical clocks and logical time
Logical clocks and logical time
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Logical clocks and logical time

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Transcript

  • 1. Logical Time and Clocks1 | Internal use only
  • 2. The need for logical time • Unlike conventional sequential programs. the computations performed by distributed systems – do not yield a linear sequence of events – system inherently define a partial ordering – genuinely concurrent events have no influence on one another. another2 | Internal use only
  • 3. The relation “happened before,” • Condition 1: Sequential behaviour. If events e and f occur in the same process instance p, and f occurs after e, – then e → f ( e happened before f ) • Condition 2: Process creation . If event e and process instance q occur in process instance p. – event f occurs in q, – and q begins after e, – then e → f3 | Internal use only
  • 4. Happened before ... • Condition 3: Process termination. If event e and process instance q occur in process instance p. – event f occurs in q. – and e occurs after q terminates. – then f → e4 | Internal use only
  • 5. Condition 4 • : Synchronous (un-buffered) message-passing. – If event e is a synchronous input (output) – and event f is the corresponding output (input), – and there is an event g such that • e → g, • then f → g. – If there is an event h such that h → e, then • h→f5 | Internal use only
  • 6. Condition 5 • Asynchronous (buffered) message-passing. – If event e is an asynchronous send and event f is the corresponding receive, • then e → f6 | Internal use only
  • 7. Condition 6 • Transitivity : –e→f –f→g – Then e → g7 | Internal use only
  • 8. Concurrent Events • a -/-> e , e -/-> a since they occur at different processes • Such events are called concurrent • Therefore a || e8 | Internal use only
  • 9. 9 | Internal use only
  • 10. Lamport Logical Clocks10 | Internal use only
  • 11. Vector time11 | Internal use only
  • 12. May be Continued ... So any12 | Internal use only
  • 13. Thank You !!13 | Internal use only

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