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Chapter 12. Distributed Database Management Systems Database Systems: Design, Implementation, and Management, Seventh Edition, Rob and Coronel. In this chapter, you will learn:. What a distributed database management system (DDBMS) is and what its components are

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Chapter 12

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Chapter 12

Chapter 12

Distributed Database Management Systems

Database Systems: Design, Implementation, and Management, Seventh Edition, Rob and Coronel


In this chapter you will learn

In this chapter, you will learn:

  • What a distributed database management system (DDBMS) is and what its components are

  • How database implementation is affected by different levels of data and process distribution

  • How transactions are managed in a distributed database environment

  • How database design is affected by the distributed database environment

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


The evolution of distributed database management systems

The Evolution of Distributed Database Management Systems

  • Distributed database management system (DDBMS)

    • Governs storage and processing of logically related data over interconnected computer systems in which both data and processing functions are distributed among several sites

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


The evolution of distributed database management systems continued

The Evolution of Distributed Database Management Systems (continued)

  • Centralized database required that corporate data be stored in a single central site

  • Dynamic business environment and centralized database’s shortcomings spawned a demand for applications based on data access from different sources at multiple locations

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


The evolution of distributed database management systems continued1

The Evolution of Distributed Database Management Systems (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Ddbms advantages and disadvantages

DDBMS Advantages and Disadvantages

  • Advantages include:

    • Data are located near “greatest demand” site

    • Faster data access

    • Faster data processing

    • Growth facilitation

    • Improved communications

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Ddbms advantages and disadvantages continued

DDBMS Advantages and Disadvantages (continued)

  • Advantages include (continued):

    • Reduced operating costs

    • User-friendly interface

    • Less danger of a single-point failure

    • Processor independence

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Ddbms advantages and disadvantages continued1

DDBMS Advantages and Disadvantages (continued)

  • Disadvantages include:

    • Complexity of management and control

    • Security

    • Lack of standards

    • Increased storage requirements

    • Increased training cost

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Ddbms advantages and disadvantages continued2

DDBMS Advantages and Disadvantages (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Ddbms advantages and disadvantages continued3

DDBMS Advantages and Disadvantages (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Ddbms advantages and disadvantages continued4

DDBMS Advantages and Disadvantages (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Characteristics of distributed management systems

Characteristics of Distributed Management Systems

  • Application interface

  • Validation

  • Transformation

  • Query optimization

  • Mapping

  • I/O interface

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Characteristics of distributed management systems continued

Characteristics of Distributed Management Systems (continued)

  • Formatting

  • Security

  • Backup and recovery

  • DB administration

  • Concurrency control

  • Transaction management

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Characteristics of distributed management systems continued1

Characteristics of Distributed Management Systems (continued)

  • Must perform all the functions of centralized DBMS

  • Must handle all necessary functions imposed by distribution of data and processing

    • Must perform these additional functions transparently to the end user

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Characteristics of distributed management systems continued2

Characteristics of Distributed Management Systems (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Ddbms components

DDBMS Components

  • Must include (at least) the following components:

    • Computer workstations

    • Network hardware and software

    • Communications media

    • Transaction processor (application processor, transaction manager)

      • Software component found in each computer that requests data

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Ddbms components continued

DDBMS Components (continued)

  • Must include (at least) the following components (continued):

    • Data processor or data manager

      • Software component residing on each computer that stores and retrieves data located at the site

      • May be a centralized DBMS

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Ddbms components continued1

DDBMS Components (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Levels of data and process distribution

Levels of Data and Process Distribution

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Single site processing single site data spsd

Single-Site Processing, Single-Site Data (SPSD)

  • All processing is done on single CPU or host computer (mainframe, midrange, or PC)

  • All data are stored on host computer’s local disk

  • Processing cannot be done on end user’s side of system

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Single site processing single site data spsd continued

Single-Site Processing, Single-Site Data (SPSD) (continued)

  • Typical of most mainframe and midrange computer DBMSs

  • DBMS is located on host computer, which is accessed by dumb terminals connected to it

  • Also typical of first generation of single-user microcomputer databases

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Single site processing single site data spsd continued1

Single-Site Processing, Single-Site Data (SPSD) (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Multiple site processing single site data mpsd

Multiple-Site Processing, Single-Site Data (MPSD)

  • Multiple processes run on different computers sharing single data repository

  • MPSD scenario requires network file server running conventional applications that are accessed through LAN

  • Many multiuser accounting applications, running under personal computer network, fit such a description

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Multiple site processing single site data mpsd continued

Multiple-Site Processing, Single-Site Data (MPSD) (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Multiple site processing multiple site data mpmd

Multiple-Site Processing, Multiple-Site Data (MPMD)

  • Fully distributed database management system with support for multiple data processors and transaction processors at multiple sites

  • Classified as either homogeneous or heterogeneous

  • Homogeneous DDBMSs

    • Integrate only one type of centralized DBMS over a network

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Multiple site processing multiple site data mpmd continued

Multiple-Site Processing, Multiple-Site Data (MPMD) (continued)

  • Heterogeneous DDBMSs

    • Integrate different types of centralized DBMSs over a network

  • Fully heterogeneous DDBMS

    • Support different DBMSs that may even support different data models (relational, hierarchical, or network) running under different computer systems, such as mainframes and microcomputers

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Multiple site processing multiple site data mpmd continued1

Multiple-Site Processing, Multiple-Site Data (MPMD) (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Distributed database transparency features

Distributed Database Transparency Features

  • Allow end user to feel like database’s only user

  • Features include:

    • Distribution transparency

    • Transaction transparency

    • Failure transparency

    • Performance transparency

    • Heterogeneity transparency

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Distribution transparency

Distribution Transparency

  • Allows management of physically dispersed database as though it were a centralized database

  • Following three levels of distribution transparency are recognized:

    • Fragmentation transparency

    • Location transparency

    • Local mapping transparency

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Distribution transparency continued

Distribution Transparency (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Distribution transparency continued1

Distribution Transparency (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Transaction transparency

Transaction Transparency

  • Ensures database transactions will maintain distributed database’s integrity and consistency

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Distributed requests and distributed transactions

Distributed Requests and Distributed Transactions

  • Distributed transaction

    • Can update or request data from several different remote sites on network

  • Remote request

    • Lets single SQL statement access data to be processed by single remote database processor

  • Remote transaction

    • Accesses data at single remote site

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Distributed requests and distributed transactions continued

Distributed Requests and Distributed Transactions (continued)

  • Distributed transaction

    • Allows transaction to reference several different (local or remote) DP sites

  • Distributed request

    • Lets single SQL statement reference data located at several different local or remote DP sites

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Distributed requests and distributed transactions continued1

Distributed Requests and Distributed Transactions (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Distributed requests and distributed transactions continued2

Distributed Requests and Distributed Transactions (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Distributed requests and distributed transactions continued3

Distributed Requests and Distributed Transactions (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Distributed requests and distributed transactions continued4

Distributed Requests and Distributed Transactions (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Distributed requests and distributed transactions continued5

Distributed Requests and Distributed Transactions (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Distributed concurrency control

Distributed Concurrency Control

  • Multisite, multiple-process operations are much more likely to create data inconsistencies and deadlocked transactions than are single-site systems

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Distributed concurrency control continued

Distributed Concurrency Control (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Two phase commit protocol

Two-Phase Commit Protocol

  • Distributed databases make it possible for transaction to access data at several sites

  • Final COMMIT must not be issued until all sites have committed their parts of transaction

  • Two-phase commit protocol requires each individual DP’s transaction log entry be written before database fragment is actually updated

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Performance transparency and query optimization

Performance Transparency and Query Optimization

  • Objective of query optimization routine is to minimize total cost associated with execution of request

  • Costs associated with request are function of:

    • Access time (I/O) cost

    • Communication cost

    • CPU time cost

  • Must provide distribution transparency as well as replica transparency

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Performance transparency and query optimization continued

Performance Transparency and Query Optimization (continued)

  • Replica transparency

    • DDBMS’s ability to hide existence of multiple copies of data from user

  • Query optimization techniques include:

    • Manual or automatic

    • Static or dynamic

    • Statistically based or rule-based algorithms

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Distributed database design

Distributed Database Design

  • Data fragmentation

    • How to partition database into fragments

  • Data replication

    • Which fragments to replicate

  • Data allocation

    • Where to locate those fragments and replicas

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Data fragmentation

Data Fragmentation

  • Breaks single object into two or more segments or fragments

  • Each fragment can be stored at any site over computer network

  • Information about data fragmentation is stored in distributed data catalog (DDC), from which it is accessed by TP to process user requests

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Data fragmentation continued

Data Fragmentation (continued)

  • Strategies

    • Horizontal fragmentation

      • Division of a relation into subsets (fragments) of tuples (rows)

    • Vertical fragmentation

      • Division of a relation into attribute (column) subsets

    • Mixed fragmentation

      • Combination of horizontal and vertical strategies

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Data fragmentation continued1

Data Fragmentation (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Data fragmentation continued2

Data Fragmentation (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Data fragmentation continued3

Data Fragmentation (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Data fragmentation continued4

Data Fragmentation (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Data fragmentation continued5

Data Fragmentation (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Data fragmentation continued6

Data Fragmentation (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Data fragmentation continued7

Data Fragmentation (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Data replication

Data Replication

  • Storage of data copies at multiple sites served by computer network

  • Fragment copies can be stored at several sites to serve specific information requirements

    • Can enhance data availability and response time

    • Can help to reduce communication and total query costs

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Data replication continued

Data Replication (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Data replication continued1

Data Replication (continued)

  • Replication scenarios

    • Fully replicated database

      • Stores multiple copies of each database fragment at multiple sites

      • Can be impractical due to amount of overhead

    • Partially replicated database

      • Stores multiple copies of some database fragments at multiple sites

      • Most DDBMSs are able to handle the partially replicated database well

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Data replication continued2

Data Replication (continued)

  • Replication scenarios (continued)

    • Unreplicated database

      • Stores each database fragment at single site

      • No duplicate database fragments

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Data allocation

Data Allocation

  • Deciding where to locate data

  • Allocation strategies

    • Centralized data allocation

      • Entire database is stored at one site

    • Partitioned data allocation

      • Database is divided into several disjointed parts (fragments) and stored at several sites

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Data allocation continued

Data Allocation (continued)

  • Allocation strategies (continued)

    • Replicated data allocation

      • Copies of one or more database fragments are stored at several sites

  • Data distribution over computer network is achieved through data partition, data replication, or combination of both

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Client server vs ddbms

Client/Server vs. DDBMS

  • Way in which computers interact to form system

  • Features user of resources, or client, and provider of resources, or server

  • Can be used to implement a DBMS in which client is the TP and server is the DP

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Client server vs ddbms continued

Client/Server vs. DDBMS (continued)

  • Client/server advantages

    • Less expensive than alternate minicomputer or mainframe solutions

    • Allow end user to use microcomputer’s GUI, thereby improving functionality and simplicity

    • More people in job market have PC skills than mainframe skills

    • PC is well established in workplace

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Client server vs ddbms continued1

Client/Server vs. DDBMS (continued)

  • Client/server advantages (continued)

    • Numerous data analysis and query tools exist to facilitate interaction with DBMSs available in PC market

    • Considerable cost advantage to offloading applications development from mainframe to powerful PCs

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Client server vs ddbms continued2

Client/Server vs. DDBMS (continued)

  • Client/server disadvantages

    • Creates more complex environment

      • Different platforms (LANs, operating systems, and so on) are often difficult to manage

    • An increase in number of users and processing sites often paves the way for security problems

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Client server vs ddbms continued3

Client/Server vs. DDBMS (continued)

  • Client/server disadvantages (continued)

    • Possible to spread data access to much wider circle of users

      • Increases demand for people with broad knowledge of computers and software

      • Increases burden of training and cost of maintaining the environment

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


C j date s twelve commandments for distributed databases

C. J. Date’s Twelve Commandments for Distributed Databases

  • Local site independence

  • Central site independence

  • Failure independence

  • Location transparency

  • Fragmentation transparency

  • Replication transparency

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


C j date s twelve commandments for distributed databases continued

C. J. Date’s Twelve Commandments for Distributed Databases (continued)

  • Distributed query processing

  • Distributed transaction processing

  • Hardware independence

  • Operating system independence

  • Network independence

  • Database independence

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Summary

Summary

  • Distributed database stores logically related data in two or more physically independent sites connected via computer network

  • Distributed processing is division of logical database processing among two or more network nodes

  • Distributed databases require distributed processing

  • Main components of DDBMS are transaction processor and data processor

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Summary continued

Summary (continued)

  • Current database systems can be classified by extent to which they support processing and data distribution

  • Homogeneous distributed database system integrates only one particular type of DBMS over computer network

  • Heterogeneous distributed database system integrates several different types of DBMSs over computer network

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Summary continued1

Summary (continued)

  • DDBMS characteristics are best described as set of transparencies

  • Transaction is formed by one or more database requests

  • Distributed concurrency control is required in network of distributed databases

  • Distributed DBMS evaluates every data request to find optimum access path in distributed database

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


Summary continued2

Summary (continued)

  • The design of distributed database must consider fragmentation and replication of data

  • Database can be replicated over several different sites on computer network

  • Client/server architecture refers to way in which two computers interact over computer network to form a system

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel


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