Distributed Operating Systems (Unit 4)

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 Distributed Operating Systems (Unit 4)

Scheduling

Normal time-sharing scheduling algorithms could lead to latency issues. When a processor tries to call another processor which will only get executed in the next time slice, it only increases the execution time.
  • Co-Scheduling - Uses a conceptual matrix in which each particular processor which is being called is in a particular row. This makes a round-robin scheduling algorithm with all processors running first the processor for a fixed time then, the next, and so on.
  • Real-time
  • Static
  • Dynamic

Fault Classifications

  • Component Faults
    • Transient - Can occur once and then disappear.
    • Intermittent - Can occur, disappear, and reoccur later.
    • Permanent - They stay till the component is repaired.
  • System Failures - Processor Faults
    • Fail Silent - Just stops upon fault and does not respond.
    • Byzantine - Continues to run and gives malicious or wrong output.
  • Synchronous - Responds to a message within known finite bound if working.
  • Asynchronous
  • Redundancy
    • Information
    • Time - More time for intermittent and transient faults.
    • Physical - Extra equipment for better fault detection.
    • Active Replication - Uses physical redundancy (same as Triple Modular)
    • Primary Backup - Primary server works, when down, the backup takes a load.

    • Triple Modular

Threads


System Models

  • Workstation model
    • Diskless
    • Diskful
    • Hybrid
    • Idle

Design Issues of Processor Allocation Algorithms

  • Deterministic vs Heuristic
  • Centralised vs Decentralised
  • Optimal vs sub-optimal
  • Local vs Global
  • Sender Initialted vs Receiver Initiated.

Processor Allocation Algorithms


Dynamic Load Distribution Components

Dynamic Load Distribution Algorithms

  • Centralised
  • Hierarchical

  • Sender-Initiated

  • Receiver-Initiated

  • Bidding

  • Direct
  • Nearest Neighbour

RTS







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