Lecture Notes Unit3 chapter22 - distributed databases

Description:
Welcome to the comprehensive guide on Relational Database Management System (RDBMS) concepts, tailored for final year B.Sc. Computer Science students affiliated with Alagappa University. This document covers fundamental principles and advanced topics in RDBMS, offering a structured approach to understanding databases in the context of modern computing. PDF content is prepared from the text book databse system concepts by siberschatz, Korth and sudharsan

Key Topics Covered:

Main Topic : Distributed Databases
Sub-Topic :
Homogeneous and Heterogeneous Databases- Distributed Data Storage - Data Replication - Data Fragmentation - Distributed Transactions -Distributed Query Processing - Query Transformation -
Target Audience:
Final year B.Sc. Computer Science students at Alagappa University seeking a solid foundation in RDBMS principles for academic and practical applications.

URL for previous slides

Unit 3 - part 2: https://www.slideshare.net/slideshow/lecture-notes-unit3-chapter21-parallel-databases/272417651
Unit 3: https://www.slideshare.net/slideshow/lecture-notes-unit3-chapter20-database-system-architectures/272417221

Unit 2:
https://www.slideshare.net/slideshow/lecture-notes-unit2-chapter7-relationaldatabasedesign/271859844
Unit I:
Chapter 6 : Database Design and ER Model https://www.slideshare.net/slideshow/lecture-notes-unit-1-chapter-6-e-r-model/271813542
Chapter 1 : Introduction to DBMS
https://www.slideshare.net/slideshow/lecture-notes-unit1-chapter1-introduction/271392881

Unit V
Chapter 20:
https://www.slideshare.net/slideshow/lecture-notes-unit5-chapter20-transaction/270998760
Chapter 19:
https://www.slideshare.net/slideshow/lecture-notes-unit5-chapter19-cursor-in-pl-sql/270998251
Chapter 18: https://www.slideshare.net/slideshow/lecture-notes-unit5-chapter18-packages-pdf/270845026
Chapter 17: https://www.slideshare.net/slideshow/lecture-notes-unit5-chapter17-stored-procedures-and-functions/270844763
Chapter 16 : https://www.slideshare.net/slideshow/lecture-notes-unit5-chapter16-trigger-creation/270631080
Chapter 15 : https://www.slideshare.net/slideshow/lecture-notes-unit5-chapter-15-pl-sql-programming/270383949

Unit IV

Chapter 14 Synonym : https://www.slideshare.net/slideshow/lecture_notes_unit4_chapter14_synonyms-pdf/270327685
Chapter 13 Users, Privileges : https://www.slideshare.net/slideshow/lecture-notes-unit4-chapter13-users-roles-and-privileges/270304806
Chapter 12 View : https://www.slideshare.net/slideshow/rdbms-lecture-notes-unit4-chapter12-view/270199683
Chapter 11 Sequence: https://www.slideshare.net/slideshow/sequnces-lecture_notes_unit4_chapter11_sequence/270134792
chapter 8,9 and 10 : https://www.slideshare.net/slideshow/lecture_notes_unit4_chapter_8_9_10_rdbms-for-the-students-affiliated-by-alagappa-university/270123800

About the Author:
Dr. S. Murugan is Associate Professor at Alagappa Government Arts College, Karaikudi. With 23 years of teaching experience in the field of Computer Science.

1. RDBMS -Unit III
Chapter 22
Distributed Databases
Prepared By
Dr.S.Murugan, Associate Professor
Department of Computer Science,
AlagappaGovernmentArts College, Karaikudi.
(Affiliated by AlagappaUniversity)
Mailid: [email protected]
Reference Book:
Database System Concepts by Abraham Silberschatz, Henry
F.Korth, S. Sudharshan

2. 22.1 Homogeneous and Heterogeneous Databases
➢Inahomogeneousdistributeddatabasesystem,all
siteshaveidenticaldatabasemanagementsystem
software,areawareofoneanother,andagreeto
cooperateinprocessingusers'requests.(Ex:All
systemusesoracleDB)
➢Inaheterogeneousdistributeddatabase,differentsites
mayusedifferentschemas,anddifferentdatabase-
managementsystemsoftware.
➢Thesitesmaynotbeawareofoneanother.(Ex:One
systemusesoracleothersystemmayuseAccess)

3. 22.2 Distributed Data Storage
➢Considerarelationrthatistobestoredinthe
database.Therearetwoapproachestostoringthis
relationinthedistributeddatabase:
➢Replication:Thesystemmaintainsseveralidentical
copiesoftherelation,andstoreseachrelationin
differentsite.
➢Fragmentation:Thesystempartitionstherelation
intoseveralfragments,andstoreseachfragmentata
differentsite.(Horizondalorverticalfragmentation)

4. 22.2.1 Data Replication
➢Ifrelationrisreplicated,acopyofrelationrisstored
intwoormoresites.
➢Thereareanumberofadvantagesanddisadvantages
toreplication.
Advantage:
Availability. If one of the sites containing relation r faiIs,
then the relation r can be found in another site.
Disadvantage:
Increased parallelism: If we want to reading of the
relation r, then several sites can process queries involving
r in parallel.
Increased overhead on update: If we want to update of
the relation r, then several sites can update the relation r
in parallel.

5. 22.2.2 Data Fragmentation
➢Ifrelationrisfragmented,risdividedintoanumber
offragmentsr
1,r
2,...,r
n.
➢Therearetwodifferentschemesforfragmentinga
relation:horizontalfragmentationandvertical
fragmentation.
➢Horizontalfragmentationsplitstherelationby
assigningeachtupleofrtooneormorefragments.
➢Verticalfragmentationsplitstherelationby
decomposingtheschemeRofrelationr.

6. 22.2.2 Data Fragmentation
➢Weshallillustratetheseapproachesbyfragmenting
therelationaccount,withtheschema
➢Account-schema=(account_number,branch_name,
balance)
➢Inhorizontalfragmentation,arelationrispartitioned
intoanumberofsubsets,r
1,r
2,...,r
n.Eachtupleof
relationrmustbelongtoatleastoneofthefragments.

7. 22.2.2 Data Fragmentation
➢Forexample,theaccountrelationcanbedividedinto
severaldifferentfragments,eachofwhichconsistsof
tuplesofaccountsbelongingtoaparticularbranch.
➢Ifthebankingsystemhasonlytwobranches-Hillside
andValleyview-thentherearetwodifferent
fragments:
➢Wereconstructtherelationrbytakingtheunionofall
fragments

8. 22.2.2 Data Fragmentation
➢Verticalfragmentationofr(R)involvesthedefinition
ofseveralsubsetsofattributesR
1,R
2,...,R
nofthe
schemaRsothat
➢Forex,considerauniversitydatabasewitharelation
employee-info=employee-id,name,designation,salary.
➢Theemployee_inforelationmaybefragmentedinto
tworelation.
Employee_private-info=employee-id,salary
employee_public-info=employee-id,name,designation.
➢Thesemaybestoredatdifferentsites.

9. 22.3 Distributed Transactions
➢Accesstothevariousdataitemsinadistributed
systemisusuallyaccomplishedthroughtransactions,
whichmustpreservetheACIDproperties.
➢Therearetwotypesoftransactionthatweneedto
consider.
➢Thelocaltransactionsarethosethataccessandupdate
datainonlyonelocaldatabase;
➢Theglobaltransactionsarethosethataccessand
updatedatainseverallocaldatabases.

10. 22.7 Distributed Query Processing
➢Thereareseveraltechniquesforchoosingastrategy
forprocessingaquerythatminimizetheamountof
timethatittakestocomputetheanswer.
➢Forcentralizedsystems,theprimarycriterionfor
measuringthecostofaparticularstrategyisthe
numberofdiskaccesses.
➢Inadistributedsystem,wemusttakeintoaccount
severalothermatters,including
➢Thecostofdatatransmissionoverthenetwork.
➢Thepotentialgaininperformancefromhaving
severalsitesprocesspartsofthequeryin
parallel.

11. 22.7 Distributed Query Processing
➢Ingeneral,wecannotfocussolelyondiskcostsoron
networkcosts.Rather,wemustfindagoodtrade-off
betweenthetwo.

12. 22.7.1 Query Transformation
➢Consideranextremelysimplequery:"Findallthe
tuplesintheaccountrelation.“
➢Iftheaccountrelationisreplicated,wehaveachoice
ofreplicatomake.
➢ifareplicaisfragmented,thechoiceisnotsoeasyto
make,sinceweneedtocomputeseveraljoinsor
unionstoreconstructtheaccountrelation.