Naive Vector Clocks and Singhal

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Naive Vector Clocks and Singhal Kshemkalyani's
Vector Clocks

• Presented by
• Abdulkareem Alali

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Briefly Naive Vector Clocks vs. SKs Vector
Clocks

• Naïve Vector Clocks
• Vector clock of a system of N processes is an
  array of N logical clocks, 1 per process, a local
  copy of which is kept in each process with the
  following rules for clock updates
• Initially all clocks are 0. For an internal
  event, increments its own logical clock in the
  vector by 1. Before send a message, it increments
  its own logical clock in the vector by 1. Each
  time a process receives a message, it increments
  its own logical clock in the vector by 1 and
  updates each element in its vector by taking the
  maximum of the value in its own vector clock and
  the value in the vector in the received message
  (for every element).

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Briefly Naive Vector Clocks vs. SKs Vector
Clocks cont.

• SKs Vector Clocks
• Based on the observation that between
  successive message sends to the same process,
  only a few entries of the vector clock at the
  sender process are likely to change.
• On average the size of the time stamp on a
  message will be less than N.

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Approach

• All processes start by calling the task
  Processing().
• Processing() with some probability depending
  on the MAX_NODES will update the logical clock by
  1, else will send a message randomly to other
  process.
• In case the message received at any process,
  updates hold and Processing() will be called.
• For failed message sending, A delay event will
  be invoked for IMER_ONE_SHOT 1024 and then
  Processing() will be called.

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Code Architecture

• task Processing()
• if ( choice gt P(MAX_NODES))
• /P is a probability function with a high chance
  return a number larger than choice/
• clockLOCAL_ADDRESS
• else
• target Random(MAX_NODES)
• /Random is a function the returns a random
  number between 0 - MAX_NODES/
• sendMessageTo(target)
• event receiveMessage( mptr )
• clockLOCAL_ADDRESS
• MessagesCounter
• for ( i 0 i lt MAX_NODES i)

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Conclusion

• As mentioned before we conclude that SK vector
  clocks algorithm - as in the targeted approach
  would maintain lower cost than the Naive vector
  clock implementation and that would appear
  clearly in huge systems.

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Future Work

• In general, with a much better approach we
  could have more precise results that really
  simulate the real wireless systems because
  Randomness is not what the real world behaves.
• In special, for my approach, Function P could
  be studied in more depth to have a choice more
  balanced every time. The one Im using right now
  is too simple.

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Problems

• Time shortage (my problem).
• Very hard to trace the code.
• Memory limitations.
• I faced a major problem with Random generating
  function. Till at the end I coded something on my
  own.

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THE END