UNIT 5 Parallel and Distributed Databases 1 System

UNIT 5 Parallel and Distributed Databases 1

System Architecture The architecture of a computer system is the highlevel (most general) design on which the system is based Architectural features include: Components Connectors (how components communicate) 2

Centralized Systems Run on a single computer system and do not interact with other computer systems. General-purpose computer system: one to a few CPUs and a number of device controllers that are connected through a common bus that provides access to shared memory. Single-user system (e. g. , personal computer or workstation): desk-top unit, single user, usually has only one CPU and one or two hard disks; the OS may support only one user. Multi-user system: more disks, more memory, multiple CPUs, and a multi-user OS. Serve a large number of users who are connected to the system vie terminals. Often called server systems. 3

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Multi-user DBMS architecture Teleprocessing File - Server Client-Server 5

Teleprocessing The traditional architecture for multi-user systems was Teleprocessing, where there is : § § One computer with a single Central Processing Unit (CPU) and A number of terminals. 6

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All processing is performed within the boundaries of the same physical computer. User terminals are typically the 'Dumb Terminals'. They are incapable of functioning at their own and they are attached by cable to the central computer. The terminals send messages via. the communication control sub-system 8

File Server In a file server environment, the processing is distributed about the network, typically the Local Area Network (LAN). The file server holds the files required by the application and the DBMS. However, the applications and DBMS run on each workstation, requesting files from the file server when necessary 9

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The file server acts simply as a shared data disk. The DBMS on each workstation sends requests to the file server for all data that the DBMS requires that it is stored on disk. This approach can generate significant amount of network traffic, which can lead to performance problems. 11

The file server architecture has three main disadvantages: There is a large amount of network traffic. A full copy of DBMS is required on each workstation. 12

Client Server Architecture A network architecture in which each computer or process on the network is either a client or a server. 13

Client-Server Architecture The Web is a client-server system Web browsers act as clients, and make requests to web servers Web servers respond to requests with requested information and/or computation Client Server Client request 14

Components Clients Servers Communication Networks Server Client 15

Client-Server Architecture Each component of a client-server system has the role of either client or server Client: a component that makes requests clients are active initiators of transactions Server: a component that satisfies requests servers are passive and react to client requests 16

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Interconnection Network Architectures Bus. System components send data on and receive data from a single communication bus; Does not scale well with increasing parallelism. Mesh. Components are arranged as nodes in a grid, and each component is connected to all adjacent components Communication links grow with growing number of components, and so scales better. Hypercube. Components are numbered in binary; components are connected to one another if their binary representations differ in exactly one bit. 18

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Clients Applications that run on computers Rely on servers for Clients are Applications Files Devices Processing power Example: E-mail client An application that enables you to send and receive email 20

Servers Computers or processes that manage network resources Servers Manage Resources Disk drives (file servers) Printers (print servers) Network traffic (network servers) Example: Database Server A computer system that processes database queries 21

Types of Servers Application Servers Audio/Video Servers Chat Servers Fax Servers FTP Servers Groupware Servers List Servers Mail Servers News Servers Proxy Servers Telnet Servers Web Servers Source: http: //webopedia. lycos. com 22

Client–Server Computing Process takes place on the server and on the client Client-Server Computing Optimizes Computing Resources Servers Store and protect data Process requests from clients Clients Make requests Format data on the desktop 23

Application Functions Software application functions are separated into three distinct parts Server: Data Management Client: Presentation & Application Logic 24

1. 1. Client/Server Environment clients LAN or WAN network Server Data 25

1. 2. Example The ATM network: the clients are the ATM machines user interfaces; some simple application processing the server is at the bank most application processing; very large database of customer accounts 26

1. 3. Architectural Requirements • Reliable, robust communication between the clients and server. • Client/server cooperation – started by the client • Application processing is usually distributed between a client and the server. • Server controls services/data that the client accesses. • Server handles conflicting requests. 27

Database functionality can be divided into: Back-end: manages access structures, query evaluation and optimization, concurrency control and recovery. Front-end: consists of tools such as forms, report-writers, and graphical user interface facilities. The interface between the front-end and the back-end is through SQL or through an application program interface. 28

2. 3. The 2 -tier Model Client Presentation Logic Business Logic Database Logic Server Database Logic DBMS Data base 29

2 -Tier C-S Architecture Tier 1: Client platform, hosting a web browser Tier 2: server platform, hosting all server software components 30

2 -Tier Characteristics Advantage: Inexpensive (single platform) Disadvantages Interdependency (coupling) of components No redundancy Limited scalability Typical application 10 -100 users Small company or organization, e. g. , law office, medical practice, local non-profit 31

3 -Tier C-S Architecture Tier 3 takes over part of the server function from tier 2, typically data management 32

3 -Tier Characteristics Advantages Improved performance, from specialized hardware Decreased coupling of software components Improved scalability Disadvantages No redundancy Typical Application 100 -1000 users Small business or regional organization, e. g. , specialty retailer, small college 33