Lecture 4

• Lecture 4
  • Video
  • Slides
  • Topic
  • Reference
  • What is a distributed system
  • Issues in designing distributed systems
    • global knowledge
    • Scalability issue
    • Compatibility
    • Process synchronization
    • Resource management
    • Issues contd
    • Distributed Scheduling
    • Security
    • Structuring

Video

link

Slides

link

Topic

• introduction to distrubuted systems and design issues

Reference

• ch5 of singhal and shivratri book
  • clock synchronization

What is a distributed system

• several computers are there
• do not share memory or clock
• communicate with each other by way of msg passing
  • shared memory system are not distributed systems
• each system has own memory and os
• are autonomous
  • are able to act independently
    • decision they take are based on knowledge they have and they acquire by message passing
  • resources they own and control are local
    • do not own any resource physically unavailable to them
  • resources owned and controlled by other computers are remote
    • to access them, u have to request
  • accessing remote resources is expensive
    • due to communication delays, cpu overhead in processing communicaton protocols

Issues in designing distributed systems

• how communication is handled b/w computers
• how programs communicate to perform distributed computations

global knowledge

• global entire state of system is not accurately/completely known at all points of time
• but in order to make any efficient decision, I might need knowledge of whole system (to a good degree of accuracy)

• how to do temporal ordering of events if global clock nahi hai

Scalability issue

• system availability
• performance
• protocols
  • broadcast based works for small systems
  • gossip protocol
    • works on concepts of epidemic
    • how an epidemic spreads
• If the requirement of scarce resource increase linearly with the number of computers in the system, it is likely to be too costly to implement
  • A design requiring that info regarding system’s configuration or directories be stored at every computer

Compatibility

• interoperability among the reosurces
• three levels
  • binary
    • says all processes execute same binary instructions even tho they may differ in i/o
    • easier system development : code for many functions directly depends on the underlying machine level instructions
    • distributed system cannot include systems with diff architectures from same or diff vendors
  • execution
    • same source code can be compiled and execured properly on any computer in the system
  • protocol level
    • least restrictive

Process synchronization

Resource management

Issues contd

Distributed Scheduling

Security

Structuring