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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 ProcessingChapter 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.

• 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.

### 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

### 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

### 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

### Distributed System - Scalibility and Heterogeneity

1.1

A distributed system organized as middleware. Heterogeneity and Scalability

### Distributed System - Transparency

Different forms of transparency in a distributed system.

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

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

1.6

### Multiprocessors (1)

• A bus-based multiprocessor.

1.7

### Multiprocessors (2)

(a) A crossbar switch

(b) An omega switching network

1.8

(a) Grid

(b) Hypercube

### Software Concepts

• An overview of

• DOS (Distributed Operating Systems)

• NOS (Network Operating Systems)

• Middleware

### Issues in System Design

• Transparency

• Flexibility

• Reliability

• Performance

• Scalability

• Interoperability

### Transparency

• Location

• Migration

• Duplication

• Relocation

• Concurrency

• Parallelism

• Location

• Access

### 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

### 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

### 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

??

### Granularity of Parallelism

• 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

### Interoperability

• Easy to collaborate with other systems in run-time

• Compatibility, Portability

• How to achieve Interoperability

• Well-Defined API set

• Standardization

1.6

### Multiprocessors (1)

• A bus-based multiprocessor.

1.7

### Multiprocessors (2)

(a) A crossbar switch

(b) An omega switching network

1.8

(a) Grid

(b) Hypercube