distributed database systems lecture no 1

8/8/2019 Distributed Database Systems Lecture No 1

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NEED OF DISTRIBUTED DATABASE

SYSTEM

Organization size

Organization Branches

Computerize Information System at each site

Single data at different location

y How to best utilize the resources ?

y How to maintain the integrity of data at different

location?


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OUTLINE

Introduction

What is a distributed DBMS

Problems

Current state-of-affairs

Background

Distributed DBMS Architecture

Distributed Database Design (Briefly)

Distributed Query Processing (Briefly)

Distributed Transaction Management (Extensive)

Mobile Database Systems (research paper based)

Privacy, Trust, and Authentication (research

paper based)

Peer to Peer Systems (research paper based)


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OUTLINE

Introduction

y What is a distributed DBMS

y Problems

y Current state-of-affairs

Background





Mobile Database Systems (research paper based)

Privacy, Trust, and Authentication (research

paper based)

Peer to Peer Systems (research paper based)


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FILE SYSTEMS

program 1

data description 1

program 2

data description 2

program 3

data description 3

File 1

File 2

File 3


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DATABASE MANAGEMENT

database

DBMS

Applicationprogram 1(with datasemantics)



description

manipulation

control


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INTEGRATE DATABASES AND COMMUINICATION

DatabaseTechnology

ComputerNetworks

integration distribution

integration

Distributed

Database

Systems


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DISTRIBUTED COMPUTING

A number of autonomous processing elements

(not necessarily homogeneous) that areinterconnected by a computer network and that

cooperate in performing their assigned tasks.


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Synonymous terms

y distributed data processing

y multiprocessors/multicomputers

y satellite processing

y backend processing

y dedicated/special purpose

computersy timeshared systems

y functionally modular systems

y Peer to Peer Systems

DISTRIBUTED COMPUTING


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Processing logic

Functions

Data

Control

WHAT IS DISTRIBUTED


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WHAT IS ADISTRIBUTED DATABASE SYSTEM?

A distributed database (DDB) is a collection of multiple,

logically interrelated databases distributed over a

computer network.

A distributed database management system (DDBMS)

is the software that manages the DDB and provides an

access mechanism that makes this distribution

transparent to the users.

Distributed database system (DDBS) = DB +

Communication


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A timesharing computer system

A loosely or tightly coupled multiprocessor system

A database system which resides at one of the

nodes of a network of computers - this is a

centralized database on a network node

WHAT IS NOT ADDBS?


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CENTRALIZED DBMS ON ANETWORK

Site 5

Site 1

Site 2

Site 3Site 4

Communication

Network


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DISTRIBUTED DBMS ENVIRONMENT

Site 5

Site 1

Site 2

Site 3Site 4

Communication

Network


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SHARED-MEMORYARCHITECTURE

Examples : symmetric multiprocessors (Sequent,

Encore) and some mainframes

(IBM3090, Bull's DPS8)

P1 Pn M

D


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SHARED-NOTHINGARCHITECTURE

Examples : Teradata's DBC, Tandem, Intel's

Paragon, NCR's 3600 and 3700

P1

M1

D1

Pn

Mn

Dn


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Manufacturing - especially multi-plant

manufacturing

Military command and control

Electronic fund transfers and electronic trading

Corporate MIS

Airline restrictions

Hotel chains

Any organization which has a decentralized

organization structure

APPLICATIONS


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Transparent management of distributed,

fragmented, and replicated data

Improved reliability/availability through

distributed transactions

Improved performance

Easier and more economical system

expansion

DISTRIBUTED DBMS PROMISES


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TRANSPARENCY

Transparency is the separation of the higher levelsemantics of a system from the lower levelimplementation issues.

Fundamental issue is to provide

data independence

in the distributed environment

y Network (distribution) transparency

y Replication transparency

y Fragmentation transparency

horizontal fragmentation: selection vertical fragmentation: projection

hybrid


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TRANSPARENTACCESS

SELECT ENAME,SAL

FROM EMP,ASG,PAY

WHERE DUR > 12

AND EMP.ENO = ASG.ENOAND PAY.TITLE = EMP.TITLE Paris projects

Paris employees

Paris assignments

Boston employees

Montreal projects

Paris projects

New York projects

with budget > 200000

Montreal employees

Montreal assignments

Boston

Communication

Network

Montreal

Paris

New

York

Boston projects

Boston employees

Boston assignments

Boston projects

New York employees

New York projects

New York assignments

Tokyo


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OUTLINE

Introduction

Background


Distributed Database Design (Briefly) Distributed Query Processing (Briefly)

Distributed Transaction Management

(Extensive)

Building Distributed Database Systems

(RAID)

Mobile Database Systems

Privacy, Trust, and Authentication

Peer to Peer Systems


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DISTRIBUTED DATABASE - USERVIEW

Distributed Database


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DISTRIBUTED DBMS - REALITY

CommunicationSubsystem

UserQuery

DBMSSoftware

DBMSSoftware

UserApplication

DBMSSoftware

User

ApplicationUserQuery

DBMSSoftware

UserQuery

DBMSSoftware


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POTENTIALLYIMPROVED PERFORMANCE

Proximity of data to its points of use

y Requires some support for fragmentation and

replication

Parallelism in execution

y Inter-query parallelism

y Intra-query parallelism


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SYSTEM EXPANSION

Issue is database scaling

Peer to Peer systems

Communication overhead


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DISTRIBUTED DBMS ISSUES

Distributed Database Design

y how to distribute the database

y replicated & non-replicated database distribution

y a related problem in directory management

Query Processing

y convert user transactions to data manipulation

instructions

y optimization problem

y min{cost = data transmission + local processing}

y general formulation is NP-hard


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DISTRIBUTED DBMS ISSUES

Concurrency Control

y Synchronization of concurrent accesses

y Consistency and isolation of transactions' effects

y Deadlock management

Reliability

y How to make the system resilient to failures

y Atomicity and durability

Privacy/Security

y Keep database access private

y Protect against malicious activities

Trusted Collaborations (Emerging requirements)

y Evaluate trust among users and database sites

y Enforce policies for privacy

y Enforce integrity


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Directory

Management

RELATIONSHIP BETWEEN ISSUES

Reliability

Deadlock

Management

Query

Processing

ConcurrencyControl

Distribution

Design


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Operating System Support

y operating system with proper support for

database operations

y dichotomy between general purpose processing

requirements and database processing

requirements

Open Systems and Interoperability

y Distributed Multidatabase Systemsy More probable scenario

y Parallel issues

Network Behavior

RELATED ISSUES


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OUTLINE Introduction Background

Distributed DBMS Architecturey Introduction to Database Concepts

Architecture, Schema, Views

y Alternatives in Distributed Database Systems

y Datalogical Architecturey Implementation Alternatives

y Component Architecture




Building Distributed Database Systems (RAID)

Mobile Database Systems

Privacy, Trust, and Authentication

Peer to Peer Systems


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Background materials of database architecture

Defines the structure of the system

y components identified

y functions of each component defined

y interrelationships and interactions between

components defined

ARCHITECTURE OF ADATABASE SYSTEM


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ANSI/SPARC ARCHITECTURE

External

Schema

Conceptual

Schema

Internal

SchemaInternal view

Users

External

view

Conceptualview

External

view

External

view


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Reference Modely A conceptual framework whose purpose is to divide

standardization work into manageable pieces and to show at ageneral level how these pieces are related to one another.

Approaches

y

Component-basedComponents of the system are defined together with the

interrelationships between components.

Good for design and implementation of the system.

y Function-based

Classes of users are identified together with the functionality

that the system will provide for each class.The objectives of the system are clearly identified. But how do

you achieve these objectives?

y Data-based

Identify the different types of describing data and specify the

functional units that will realize and/or use data according tothese views.

STANDARDIZATION


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RELATION EMP [

KEY = {ENO}

ATTRIBUTES = {

ENO : CHARACTER(9)

ENAME : CHARACTER(15)TITLE : CHARACTER(10)

}

]

RELATION PAY [

KEY = {TITLE}

ATTRIBUTES = {

TITLE : CHARACTER(10)

SAL : NUMERIC(6)

}

]

CONCEPTUAL SCHEMADEFINITION


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RELATION PROJ [

KEY = {PNO}

ATTRIBUTES = {

PNO : CHARACTER(7)

PNAME : CHARACTER(20)

BUDGET : NUMERIC(7)

}

]

RELATIONASG [

KEY = {ENO,PNO}

ATTRIBUTES = {ENO : CHARACTER(9)

PNO : CHARACTER(7)

RESP : CHARACTER(10)

DUR : NUMERIC(3)

}

]

CONCEPTUAL SCHEMADEFINITION


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RELATION EMP [

KEY = {ENO}

ATTRIBUTES = {ENO : CHARACTER(9)

ENAME : CHARACTER(15)

TITLE : CHARACTER(10)

}

]

INTERNAL_REL EMPL [

INDEXON E# CALL EMINX

FIELD = {HEADER : BYTE(1)

E# : BYTE(9)

ENAME : BYTE(15)

TIT : BYTE(10)

}

]

INTERNAL SCHEMADEFINITION


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Create a BUDGET view from the PROJ relation

CREATE VIEW BUDGET(PNAME, BUD)

AS SELECTPNAME, BUDGET

FROM PROJ

EXTERNALVIEW DEFINITION EXAMPLE 1


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Create a Payroll view from relations EMP and

TITLE_SALARY

CREATE VIEW PAYROLL (ENO, ENAME, SAL)

AS SELECT

EMP.ENO,EMP.ENAME,PAY.SAL

FROM EMP, PAY

WHERE EMP.TITLE = PAY.TITLE

EXTERNALVIEW DEFINITION EXAMPLE 2

distributed database systems lecture no 1

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