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Distributed Processing Chapter 1 : Introduction PowerPoint PPT Presentation


Distributed Processing Chapter 1 : Introduction Problem There are n nodes, each of which has a value. A node wants to know the maximum value among the n nodes. Centralized Approach : A server maintains the values of n nodes and each node reports its value to the server.

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Distributed Processing Chapter 1 : Introduction

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Distributed processing chapter 1 introduction l.jpg

Distributed ProcessingChapter 1 : Introduction


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Problem

  • There are n nodes, each of which has a value. A node wants to know the maximum value among the n nodes.

  • Centralized Approach:

    • A server maintains the values of n nodes and each node reports its value to the server.

    • Then the query node sends a message to ask the maximum value to the server, which will answer to the query.

  • Distributed Approach:

    • Each node communicates with its 6 nearest neighbor nodes to inform its value.

    • Then the query node eventually finds the maximum value by exchanging information with its neighbor nodes.


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Discussion

  • Question 1: Find the algorithm for distributed approach.

  • Question 2: Compare the performance

    • In terms of the number of communications

  • Question 3: Make a comparison table for the two approaches


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Definition of a Distributed System

  • Distributed system :

    1) A collection of (scalability)

    2) independent computers that (heterogeneity)

    3) appears to its users as a single coherent system(transparency)

  • Distributed System versus Parallel System

    • Separated Operating System vs. Single Operating System

    • Message Passing vs. Shared Memory


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Why Distributed System ?

  • Performance

  • Incremental Growth (Scalability)

    • 1 single mainframe of price W

    • N small machines of price W/N

  • Fault Tolerance

    • 1 single mainframe : critical weak point

    • Failure of a machine : replacement by other machines

  • Geographical Distribution and Availability

    • Flexible configuration

      • e.g. 1 Disk server, 3 Computing servers, 1 Graphic server, etc.

    • Geographical availability


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Distributed System - Scalibility and Heterogeneity

1.1

A distributed system organized as middleware. Heterogeneity and Scalability


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Distributed System - Transparency

Different forms of transparency in a distributed system.


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Server C

Driver for B

Driver for C

Driver for A

Server B

Server A

Distributed System : Heterogeneity

Application Program or Client

Client has to be provided with one different driver for each server


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Server C

Server B

Server A

Distributed System : Heterogeneity and Object-Oriented Approach

Application Program or Client

Predefined interface

Wrapping with predefined interface

Encapsulation : Object-Oriented Approach


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Hardware Concepts : Multiprocessor

1.6


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Multiprocessors (1)

  • A bus-based multiprocessor.

1.7


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Multiprocessors (2)

(a) A crossbar switch

(b) An omega switching network

1.8


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Homogeneous Multicomputer Systems

(a) Grid

(b) Hypercube


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Software Concepts

  • An overview of

    • DOS (Distributed Operating Systems)

    • NOS (Network Operating Systems)

    • Middleware


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Issues in System Design

  • Transparency

  • Flexibility

  • Reliability

  • Performance

  • Scalability

  • Interoperability


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Transparency

  • Hiding physical details about

    • Location

    • Migration

    • Duplication

    • Relocation

    • Concurrency

    • Parallelism

    • Location

    • Access


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Flexibility

  • Should be easy to modify functionality and architecture

  • To provide with Configurability, Avalability and Autonomy

  • Micro-Kernel vs. Monolithic Kernel

    • Monolithic Kernel : Provides all functionalities of OS.example. UNIX

    • Micro-Kernel

      • Minimal subset of OS + what users want

    • Example

      • Kernel Watch


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Reliability

  • Important Goal of Distributed System

    • Reliability

    • Security

    • Fault-Tolerance

  • Failure Probability P

    • Should be P = P1·P2·P3 … ·Pn

    • But often P = P1+ P2+ P3 … + Pn in reality


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Performance and Scalability

  • Improve performance by parallelism

  • Throughput T

    • Ideally should be T = T·n when n is the number of sites

    • In reality T <T·n

      • Due to some Bottleneck

Throughput

Number of sites

??


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Granularity of Parallelism

  • Unit of Task

    • Fine-Granularity vs. Coarse Granularity

  • Fine-Granularity

    • Large number of small tasks

    • Need a large amount of inter-task communication

    • Not good for distributed system (good for Parallel system)

  • Coarse-Granularity

    • Small number of big tasks

    • Only small amount of inter-task communication

    • Good for distributed system


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Interoperability

  • Easy to collaborate with other systems in run-time

    • Compatibility, Portability

  • How to achieve Interoperability

    • Well-Defined API set

    • Standardization


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Hardware Concepts : Multiprocessor

1.6


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Multiprocessors (1)

  • A bus-based multiprocessor.

1.7


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Multiprocessors (2)

(a) A crossbar switch

(b) An omega switching network

1.8


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Homogeneous Multicomputer Systems

(a) Grid

(b) Hypercube


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