Distributed Operating Systems (Unit 3)

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Distributed Operating Systems (Unit 3)

Synchronize 2 Clocks


Physical Time Services

  • Broadcast Based - Server time is the main. It is broadcast and other systems follow this time.
    • Simple Approach

    • Berkeley Algorithm

  • Request Driven

Clock Synchronization Algorithms

  • Mean-time - The clocks are set to the mean-time of the initial representation of the clocks.

  • Centralized Algorithms
    • Cristian's

    • Berkeley

  • Decentralized Algorithms
    • Averaging - Network Time Protocol
      • Lamport Timestamps

    • Multiple External Time Sources

Mutual Exclusion Algorithms

  • Centralized

  • Distributed

  • Token Ring

Election Algorithm

  • Bully Algorithm
    1. Recogniser of no coordinator starts election.
    2. A message is sent to all higher numbers.
    3. No response makes them the coordinator.

  • Ring Algorithm
    1. The process which recognizes failure starts a stack of numbers and tells the next.
    2. The next process which encounters this acknowledges by adding its number and passing.

Properties of Transactions

  • Atomic - Indivisible
  • Consistent - No violation of basic standards.
  • Isolated - Do not interfere with each other.
  • Durable - Changes are permanent.

Concurrency Control Algorithm

  1. Locking
  2. Two-Phase Locking

  3. Optimistic Concurrency Control
  4. Time Stamps

ATM

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