DDS Lecture 2

8/18/2019 DDS Lecture 2

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Distributed DatabaseSystemsLECTURE No 2

Chapter 1: Introduction

Reference: Principles of Distributed Database Systems (2ndEdition) by M. Tamer Osu! Patric" #aldusie.

http://www.add9band.com/aa.php?isbn=ISBN:1441988335&name=Pincip!es"o#"$istib%ted"$a

tabase"Sstems

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Lecture Pan

% Data &ndependence and DistributedData Processin'

% Denition of Distributed databases

% Promises*d+anta'es of DistributedDatabases

% Tec,nical Problems to be Studied

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%Data Independence%% T,e de+elopment of D&'S heped to

(uy achie#e data independence)transparency*

% Pro+ide centrai+ed and controed datamaintenance and access

% *pplication is immune to p,ysical and

lo'ical le or'aniation

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%Data Independence%

% Distributed database system is t,e union of -,atappear to be t-o diametrically opposed approac,esto data processin': database systems andcomputer net,or-

! Computer net,or-s promote a mode o( ,or-that "oes a"ainst centrai+ation

% 0ey issues to understand t,is combination

! The most important ob.ecti#e o( D&technoo"y is inte"ration not centrai+ation

! Inte"ration is possibe ,ithout centrai+ation/i0e0/ inte"ration o( databases and net-or"in'does not mean centraliation (in fact 1uite opposite)


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%Data Independence

• 3oal of distributed databasesystems: ac,ie+e data inte'rationand data distribution transparency

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Distributed Computin"DataProcessin"00

• * distributed computin" system is a coection o(autonomous processin" eements t,at areinterconnected by a computer net-or". T,e elementscooperate in order to perform t,e assi'ned tas".

• T,e term 5distributed6 is +ery broadly used. T,e e7actmeanin' of t,e -ord depends on t,e conte7t.

% Synonymous terms:

! distributed (unction

! distributed data processin"

! mutiprocessorsmuticomputers

! sateite processin"! bac-$end processin"

! dedicatedspecia purpose computers

! timeshared systems

! (unctionay moduar systems8


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00Distributed Computin"DataProcessin"00

•

9,at can be distributed! Processin" o"ic

! unctions

! Data

! Contro

% ;lassication of distributed systems -it, respect to +arious criteria

! De"ree o( coupin"/ i0e0/ ho, cosey the processin"eements are connected

e.'.! measured as ratio of amount of data e7c,an'ed to amount oflocal processin'

-ea" couplin'! stron' couplin'

! Interconnection structure

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De3nition o( DD& and DD&'S%

% * distributed database )DD&* is a coection o( mutipe/

o"icay interreated databases distributed o+er a computernet-or"

% * distributed database mana"ement system )DD&'S* is theso(t,are that mana"es

t,e DD> and pro+ides an access mec,anism t,at ma"es t,is

distribution transparentto t,e users.

% T,e terms DD>MS and DD>S are often used interc,an'eably

% &mplicit assumptions

! Data stored at a number o( sites each site o"icay

consists o( a sin"e processor! Processors at di4erent sites are interconnected by acomputer net,or- ),e do

not consider multiprocessors in DD>MS! cf. parallel systems)

! DD&S is a database/ not a coection o( 3es )c(0 reationadata mode*0

Pacement and 1uery of data is impacted by t,e access ?


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00De3nition o( DD& andDD&'S00

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00De3nition o( DD& andDD&'S

• E5ampe: Database consists o( 6reations empoyees/ pro.ects/and

• assi'nment -,ic, are partitionedand stored at diAerent sites(fra'mentation).

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7hat is not DD&S8000

• T,e follo-in' systems are paralleldatabase systems and are 1uitediAerent from (t,ou',

related to) distributed D> systems

Shared'emory

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%7hat is not DD&S8000

SharedDis-

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%7hat is not DD&S8000

SharedNothin"

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DD& 9ppications

• Manufacturin'! especially multi


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9d#anta"es o( DistributedDatabases00

i"her reiabiity

% Replication of components

% Co sin'le points of failure

% e.'.! a bro"en communication lin" orprocessin' element does not brin' do-n t,eentire system

% Distributed transaction processin''uarantees t,e consistency of t,e databaseand concurrency

DD>

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• Impro#ed per(ormance

% Pro7imity of data to its points of use

! Reduces remote access deays

! Re;uires some support (or (ra"mentation and repication

% Parallelism in e7ecution! Inter$;uery paraeism

! Intra$;uery paraeism

% pdate and read


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Easier system e5pansion

% &ssue is database scalin'

% Emer'ence of microprocessor and -or"station

tec,nolo'ies! Net,or- o( ,or-stations much cheaperthan a

sin"e main(rame computer

% Data communication cost +ersustelecommunication cost

% &ncreasin' database sie

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Transparency

% Refers to t,e separation of t,e ,i',er


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ser -ants to see one database Pro'rammer sees many databases

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#arious forms of transparency can be distin"usihed (or

DD&'Ss:

% Cet-or" transparency (also called distributiontransparency)

! Location transparency! Namin" transparency

% Replication transparency

% Fra'mentation transparency

% Transaction transparency! Concurrency transparency

! aiure transparency

% Performance transparency

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% Net,or-Distribution transparency ao,s a userto percei#e a DD&S as a sin"e/ lo'ical entity

% T,e user is protected from t,e operational details of t,e

net-or" (or e+en does not "no- about t,e e7istence of

t,e net-or")% T,e user does not need to "no- t,e location of data

items and a command used to perform a tas" is

independent from t,e location of t,e data and t,e sitet,e tas" is performed (ocation transparency*

% * uni1ue name is pro+ided for eac, obGect in t,edatabase (namin" transparency*

! In absence o( this/ users are re;uired to embedthe ocation name as part o( an identier

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DiAerent -ays to ensure namin' transparency:

% Solution $: ;reate a central name ser+erH ,o-e+er! t,is results in

! oss o( some oca autonomy

! centra site may become a bottenec-

! o, a#aiabiity )i( the centra site (ais remainin" sites cannot createne, ob.ects*

% Solution 2: Pre7 obGect -it, identier of site t,at created it

! e0"0/ branch created at site S1 mi"ht be named S10&R9NC

! 9so need to identi(y each (ra"ment and its copies

! e0"0/ copy 2 o( (ra"ment 6 o( &ranch created at site S1 mi"ht bere(erred to as

S$.>R*C;B.F.;2

% *n approac, t,at resol+es t,ese problems uses aliases for eac, databaseobGect

! Thus/ S10&R9NC060C2 mi"ht be -no,n as oca branch by user atsite S1

! DD&'S has tas- o( mappin" an aias to appropriate database ob.ect

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Repication transparency ensures that theuser is

not in#o#ed in the mana"ement o( copies ofsome

data

% T,e user s,ould e+en not be a-are about t,ee7istence of replicas! rat,er s,ould -or" as ift,ere e7ists a sin'le copy of t,e data

% Replication of data is needed for +arious reasons

! e0"0/ increased e


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% ra"mentation transparency ensures that the user is nota,are o(

and is not in#o#ed in t,e fra'mentation of t,e data

% T,e user is not in+ol+ed in ndin' 1uery processin' strate'ies o+er

fra'ments or formulatin' 1ueries o+er fra'ments

! The e#auation o( a ;uery that is speci3ed o#er an entirereation but no, has to be performed on top of t,e fra'mentsre1uires an appropriate 1uery e+aluation strate'y

% Fra'mentation is commonly done for reasons of performance!a+ailability! and reliability

% T-o fra'mentation alternati+es

! ori+onta (ra"mentation: di#ide a reation into a subsetso( tupes

! =ertica (ra"mentation: di#ide a reation by coumns

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• Transaction transparency ensures that adistributed transactions maintain inte"rity andconsistency of t,e DD> and support concurrency

% Eac, distributed transaction is di+ided into a number

of sub


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% Concurrency transparency "uarantees that transactions must e5ecute independentyand are lo'ically consistent! i.e.! e7ecutin' a set of transactions in parallel 'i+es t,e same resultas if t,e transactions -ere e7ecuted in some arbitrary serial order.

% Same fundamental principles as for centralied D>MS! but more complicated to realie:

! DD&'S must ensure that "oba and oca transactions do not inter(ere ,ith each

ot,er

! DD&'S must ensure consistency o( a sub$transactions o( "oba transaction

% Replication ma"es concurrency e+en more complicated

! I( a copy o( a repicated data item is updated/ update must be propa"ated to acopies

! >ption 1: Propa"ate chan"es as part o( ori"ina transaction/ ma-in" it an atomic

operationH ,o-e+er! if one site ,oldin' a copy is not reac,able! t,en t,e transaction is

delayed until t,e site is reac,able.! >ption 2: Limit update propa"ation to ony those sites currenty a#aiabe?remainin"

sites are updated -,en t,ey become a+ailable a'ain.

! >ption 6: 9o, updates to copies to happen asynchronousy/ sometime a(ter the

ori'inal updateH delay in re'ainin' consistency may ran'e from a fe- seconds to

se+eral ,ours

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aiure transparency: DD&'S must ensure

atomicity and durabiity o( the "oba transaction!i.e.!

t,e sub


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Per(ormance transparency: DD&'S must per(orm as i( it ,ere a centrai+edD&'S

! DD&'S shoud not su4er any per(ormance de"radation due to thedistributed

arc,itecture

! DD&'S shoud determine most cost$e4ecti#e strate"y to e5ecute a

re;uest% Distributed Iuery Processor (DIP) maps data re1uest into an ordered se1uence of

operations on local databases

% DIP must consider fra'mentation! replication! and allocation sc,emas

% DIP ,as to decide:

! ,hich (ra"ment to access

! ,hich copy o( a (ra"ment to use

! ,hich ocation to use

% DIP produces e7ecution strate'y optimied -it, respect to some cost function

% Typically! costs associated -it, a distributed re1uest include: &O cost! ;P cost! and

communication cost

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Compicatin"actorsDisad#anta"es o( DDS

• Compe5ity

% Cost: Distributed systems re1uire additional ,ard-are(communication mec,anisms etc)! t,us increase,ard-are cost.

% Security: in DDS a net-or" is in+ol+ed -,ic, is amedium t,at ,as its o-n security re1uirements. Somaintainin' a security o+er net-or" is diJcult rat,ert,en a centralied location.

@ Inte"rity contro more di


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Technica Probems to bestudied

% Distributed database desi"n

K Bo- to fra'ment t,e data

K Partitioned data +s. replicated data

@ Distributed ;uery processin"

K Desi'n al'orit,ms t,at analye 1ueries and con+ert t,em into a series of data

manipulation operations

K Distribution of data! communication costs! etc. ,as to be considered

K Find optimal 1uery plans

@ Distributed directory mana"ement

% Distributed concurrency contro

K Sync,roniation of concurrent accesses suc, t,at t,e inte'rity of t,e D> is

maintained

K &nte'rity of multiple copies of (parts of) t,e D> ,a+e to be considered (mutual

consistency)

% Distributed deadoc- mana"ement

K Deadloc" mana'ement: pre+ention! a+oidance! detectionreco+ery

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ome 7or-

• Chapter 2: >#er#ie, o( Reationa D&'S – RD>MS concepts

– Cormaliation

– &nte'rity Rules

– SIL Iueries

• Chapter 6: Re#ie, o( Computer Net,or-s – Data ;ommunication concepts

– Types of Cet-or"s

–

Protocol Standards – >road >and Cet-or"s

– 9ireless Cet-or"

– &nternet

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9ssi"nment No 1 DDS

9ssi"nment No 1: Distributed Databases ;lass: >S 8t, ;PS

Date of Submission: $8t,

Sep 2@$2 Time of submission: $$:@ *M Mar"s: $@

'he p%pose o# this assi)nment is to )i*e o% hands on pactice. It is e+pected that st%dentswi!! so!*e

the assi)nments themse!*es. ,o!!owin) %!es wi!! app! d%in) the e*a!%ation o# assi)nment.

-heatin) #om an so%ce wi!! es%!t in eo mas in the assi)nment.

0n st%dent #o%nd cheatin) in an o# the two assi)nments s%bmitted wi!! be awaded ,)ade in the

co%se.

No assi)nment a#te d%e date/time wi!! be accepted

A 1* oo,in" is a ist o( di4erent database appications0 7hich o( the/ centrai+edor distributed/

database architecture ,oud you recommend (or each and ,hy8

a$ The in(ormation system o( a particuar hospita in a city

b$ The in(ormation system o( a &an- )i-e 9&L/'C&/ &an- 9(aah etc*

N>TE : usti(y your ans,er ,ith e5ampe


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9ssi"nment No 2 DDS

9ssi"nment No 2: Distributed Databases ;lass: >S 8t,

Shared memory #s0 'essa"e passin"

Date of Submission: $?t, Sep 2@$2 Time of submission: $$:@ *M

Mar"s: $@

Shared memory allo-s multiple processes to read and -rite data from t,e same location.

'essa"e passin" is anot,er -ay for processes to communicate: eac, process can send messa'es

to ot,er processes.

A 1: 'a-e a comparison bet,een shared memory and messa"e passin": ,here are theydi4erent and

,here are the simiar8 ou mi"ht consider di4erent modes o( messa"e passin"/ (or e5ampe,ith or

,ithout messa"e oss0

A2: Consider the actions described beo,/ in ,hich mode )shared memory or messa"e passin"*can you best

describe them8 7hy and ho,8

$. ;ommunication +ia postcard

2. Spea"in' in a room -it, t-o people

. &nstant messa'es +ia S"ype (data remains on client if partner is oine)

/. Spea"in' in a room full of people

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9ssi"nment No 6 DDS9ssi"nment No 6: Distributed Databases ;lass: >S 8t, ;PS

Date of Submission: @$st October 2@$2 Time of submission: 2:@ pm

Mar"s: @

'he p%pose o# this assi)nment is to )i*e o% hands on pactice. It is e+pected that st%dents wi!! so!*e the assi)nments themse!*es.,o!!owin) %!es wi!! app!

d%in) the e*a!%ation o# assi)nment.

• -heatin) #om an so%ce wi!! es%!t in eo mas in the assi)nment.

• 0n st%dent #o%nd cheatin) in an o# the thee assi)nments s%bmitted wi!! be awaded , )ade in the co%se.

• No assi)nment a#te d%e date/time wi!! be accepted

• 2ne )o%p o# st%dents cannot wo with same Poect 'it!e !ie the othe )o%p.

• 0 )o%p consists o# 5 st%dents.

Desi"n a database o( your o,n choice )i-e any or"ani+ation/ ospita/ &usiness 3rm/ Education/ onine ban-in"/

Transaction mana"ement/ N>/ Post

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9ssi"nment No 1Compier

9ssi"nment No 1: Compier Construction ;lass: >S 8t, ;PS

Date of Submission: $8t, Sep 2@$2 Time of submission: $@:@@ *M

Mar"s: $@

'he p%pose o# this assi)nment is to )i*e o% hands on pactice. It is e+pected that

st%dents wi!! so!*e the assi)nments themse!*es. ,o!!owin) %!es wi!! app! d%in) the

e*a!%ation o# assi)nment.

• -heatin) #om an so%ce wi!! es%!t in eo mas in the assi)nment.

• 0n st%dent #o%nd cheatin) in an o# the two assi)nments s%bmitted wi!! beawaded , )ade in the co%se.

• No assi)nment a#te d%e date/time wi!! be accepted

A 1* o, a Three$Pass Compier ,or-s8A2* 7hat is the di4erence bet,een T,o$Pass Compier and Three$Pass

Compier8 7hich compier )T,o$Pass or Three$Pass* is mosty used inthese days8

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DDS Lecture 2

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