DSConceptsDec2

8/6/2019 DSConceptsDec2

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Distributed Systems Concepts

Ch. 10 and 14-17


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gure .Skew between computer clocks

in a distributed system

Network


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gure .Clock synchronization using a

time server

mr

mtp Time server,S


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.An example synchronization

subnet in an TPimplementation

1

2

3

2

3 3

ote: Arrows denote synchronization control, numbers denotestrata.


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gure .Messages exchanged between

a pair of TP peers

Ti

Ti-1Ti-2

Ti- 3

Server B

Server A

Time

m m'

Time


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gure .Events occurring at three

processesp1

p

p

a

c

e f

1

h sical

ti e


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gure .Lamport timestamps for the

events shown in Figure 10.5

a

e f

m1

m

1

51

p1

p

p

h si altime


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gure .Vector timestamps for the

events shown in Figure 10.5

a

c

e f

m1

m

( 0 0)(1 0 0)

( 1 0) ( 0)

( )(0 0 1)

p1

p

p

h sicatime


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Figure 10.8

Detecting global propertiesp

p1

essage

garbage object

object

re erence

a. Garbage collection

p p1 ait or

ait or b. Dea loc

p p1

acti ate

passi e passi ec. er ination


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Figure 10.9

Cuts

1

1

si lti e

e10

C siste t utI siste t ut

e11

e12

e13

e20

e 21

e 22


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gure .Chandy and Lamports

snapshot algorithmMarker receiving rule for process piOnpis receipt of a markermessage over channel c:

if(pi has not yet recorded its state) it

records its process state now;

records the state ofc as the empty set;turns on recording of messages arriving over other incoming channel

else

pi records the state ofc as the set of messages it has received overc

since it saved its state.

end if

Marker sending rule for process piAfterpi has recorded its state, for each outgoing channel c:

pi sends one marker message overc

(before it sends any other message overc).


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gure .Two processes and their initial

states

p1 pc

c1

account widgets

$1000 (none)

account widgets

$ 0 000


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gure .Reachability between states in

the snapshot algorithm

init inal

snap

actual e ecution e0 e1 ...

recor ing recor ingbegins en s

pre snap e'0 e'1 ...e'R 1 post snap e'R e'R+1 ...


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Chapter 11,12, and 13

Are on transaction an concurrency controlthat are typically covered in a data basecourse.


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Ch 14: Fault Tolerance


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.A basic architectural model for

the management of replicateddata

FE

Requests and

replies

C

ReplicaC

ServiceClients Front ends

managers

RM

RMFE

RM


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Figure 14.2Services provided for process groups

Join

roupaddress

expansion

Multicastcommunication

roupsend

Failroup membershipmanagement

Leave

Process group


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Figure 14.3View-synchronous group communication

p

q

r

p crashes

view q, rview p, q, r

p

q

r

p crashes


a allowed . b allowed .

p

q

r

view p, q, r

p

q

r

p crashes


c disallowed . d disallowed .

p crashes

view q, r


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Figure 14.5

Active replication

FE CFEC RM

RM

RM


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Ch.15: Distributed MultimediaSystems


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Figure 15.1

A distributed multimedia system

Wide area gate ay ideser er

igital/radi

ser er

ide ameraa d mi e

al et r al et r


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.The window of scarcity for

computing and communicationresources

1 1

remoteogin

networfi e access

high ua ityaudio

interacti eideo

insufficient

resources

scarce

resources

a undantresources

2


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gure .Characteristics of typical

multimedia streamsData rate

(approximate)Sample or frame

sizefrequency

Telephone speech 64 kbps 8 bits 8000/secCD-quality sound 1.4 Mbps 16 bits 44,000/secStandard TV video(uncompressed)

120 Mbps up to 640x 480pixelsx 16 bits

24/sec

Standard TV video(MPEG-1 compressed)

1.5 Mbps variable 24/sec

HDTV video(uncompressed)

10003000 Mbpsup to 1920x 1080pixelsx 24 bits

2460/sec

HDTV videoMPEG-2 compressed)

1030 Mbps variable 2460/sec


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.Typical infrastructure

components for multimediaapplications

Microphones

Camera

Screen

indowsystem

CodecD

B Mixer

PC workstation PC workstation

CVideostore

etworkconnections

K

L

M

: multimediastream

CodecA

Codec

H

indowsystem

hite boxes represent media processing components,many of which are implemented in software, including:codec:coding decodingfilter

mixer: sound-mixingcomponent

Videofile system


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.QoS specifications for

components of the applicationshown in Figure 15.4Component Bandwidth Latency Loss rate Resources required Camera Out: 10 frames/sec, raw video

640x480x16 bitsZero

A Codec In:

Out:

10 frames/sec, raw video

MPEG-1 stream

Interactive Low 10 ms CPU each 100 ms;

10 Mbytes RAMB Mixer In:

Out:

2 44 kbps audio

1 44 kbps audio

Interactive Very low 1 ms CPU each 100 ms;

1 Mbytes RAM

H Windowsystem

In:

Out:

various

50 frame/sec framebuffer

Interactive Low 5 ms CPU each 100 ms;

5 Mbytes RAM

K Networkconnection

In/Out: MPEG-1 stream, approx.1.5 Mbps

Interactive Low 1.5 Mbps, low-lossstream protocol

L Network connection

In/Out: Audio 44 kbps Interactive Very low 44 kbps, very low-lossstream protocol


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Figure 15.8

The RFC 1363 Flow SpecProtocol version

Maximum transmission unit

Token bucket rate

Token bucket sizeMaximum transmission rate

Minimum delay noticed

Maximum delay variation

Loss sensitivity

Burst loss sensitivity

Loss interval

Quality of guarantee

Bandwidth:

Delay:

Loss:


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Figure 15.9

Filtering

Source Targets

Highbandwidth

Mediumbandwidth

Lowbandwidth


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gure .Tiger video file server hardware

configurationController

Cub 0 Cub 1 Cub 2 Cub 3 Cub n

ATM switching network

video distribution to clientsStart Stop

requests from clients

low-bandwidth network

high-bandwidth

0 n 1 1 n 2 2 n 3 n 4 n 2n 13


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Figure 15.11

Tiger schedule

012

slot 0

viewer 4

slot 1

free

slot 2

free

slot 3

viewer 0

slot 4

viewer 3

slot 5

viewer 2

slot 6

free

slot 7

viewer 1

block play timeT

block servicetimet

state state state state state


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16: Distributed Shared Memory


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gure .The distributed shared memory

abstraction

hysicalmemory

rocess

accessing

a ears asmemory in address

s ace of rocess

hysicalmemory

hysicalmemory

istributed shared memory


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Figure 16.2

Mether system program - slide 1#include "world.h"struct shared { int a,b; };

Program Writer:

main()

{ struct shared *p;

methersetup(); /* Initialize the Mether run-time */

p = (struct shared *)METHERBASE;

/* overlay structure on METHER segment */

p->a = p->b = 0; /* initialize fields to zero */

while(TRUE) { /* continuously update structure fields */ p >a = p >a + 1;

p >b = p >b - 1;

}

}

Continuedon nextslide...


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Figure 16.2

Mether system program - slide 2ProgramReader:main()

{

struct shared *p;

methersetup();p = (struct shared *)METHERBASE;

while(TRUE) { /* read the fields once every second *

printf("a = %d, b = %d\n", p >a, p >b);

sleep(1);

}

}


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Figure 16.5

DSM using write-update

time

time

a ;

;

i t en

print "a ter" ;

i a t en

1;...

i a t en print " e re" ;

time

updates


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Figure 16.6

Data items laid out over pages

A B

page n 1page n


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gure .IDL interfaces Shape and

ShapeListstructRectangle{

1

long width;

long height;

long x;

long y;

} ;

struct GraphicalObject{ 2

string type;

Rectangle enclosing;

boolean isFilled;

};

interface Shape { 3long getVersion() ;

GraphicalObject getAllState() ; // returns state of the GraphicalObject

};

typedef sequence All; 4

interface ShapeList { 5

exception FullException{ }; 6

Shape newShape(in GraphicalObject g) raises (FullException); 7

All allShapes(); // returns sequence of remote object references 8

long getVersion() ;

};


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.Java interface ShapeListgeneratedby idltojava from C RBA interface

ShapeList

public interface ShapeList extends org.omg.CORBA.Object {

Shape newShape(GraphicalObject g) throws ShapeListPackage.FullException;Shape[] allShapes();

int getVersion();

}


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Figure 17.4

Java class ShapeListServerimport org.omg.CosNaming.*;import org.omg.CosNaming.NamingContextPackage.*;

import org.omg.CORBA.*;

public class ShapeListServer {

public static void main(String args[]) {

try{

ORB orb = ORB.init(args, null); 1ShapeListServant shapeRef = new ShapeListServant(orb); 2

orb.connect(shapeRef); 3

org.omg.CORBA.Object objRef =

orb.resolve_initial_references("NameService"); 4

NamingContext ncRef = NamingContextHelper.narrow(objRef);

NameC

omponent nc = new NameC

omponent("ShapeList", ""); 5NameComponent path[] = {nc}; 6

ncRef.rebind(path, shapeRef); 7

java.lang.Object sync = new java.lang.Object();

synchronized (sync) { sync.wait();}

} catch (Exception e) { ... }

}

gure


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gure .Java client program for C RBA

interfaces Shape and ShapeListimport org.omg.CosNaming.*;import org.omg.CosNaming.NamingContextPackage.*;import org.omg.CORBA.*;

public class ShapeListClient{

public static void main(String args[]) {

try{

ORB orb = ORB.init(args, null);

1

org.omg.CORBA.Object objRef =

orb.resolve_initial_references("NameService");

NamingContext ncRef = NamingContextHelper.narrow(objRef);

NameComponent nc = new NameComponent("ShapeList", "");

NameComponent path [] = { nc };

ShapeList shapeListRef =

ShapeListHelper.narrow(ncRef.resolve(path));

2

Shape[] sList = shapeListRef.allShapes();

3

GraphicalObject g = sList[0].getAllState();

gure


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gure .The main components of the

C RBA architecture

client server

proxy

or dynamic invocation

implementationrepository ob ect

adapter

RBRB

skeleton

or dynamic skeleton

clientprogram

interfacerepository

Request

Replycorecorefor A

ServantA


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Figure 17.7

IDL module hiteboardmodule Whiteboard {struct Rectangle{

...} ;

struct GraphicalObject {

...};

interface Shape {

...};

typedef sequence All;

interface ShapeList {...};

};


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Figure 17.8

IDL constructed types 1Type Examples Usesequence typedef sequence All;

typedef sequence Allbounded and unbounded sequencesof Shapes

Defines a type for a variable-lengthsequence of elements of a specifiedIDL type. An upper bound on thelength may be specified.

string String name;typedef string SmallString;

unboundedand boundedsequences of characters

Defines a sequences of characters,terminated by the null character. An

upper bound on the length may bespecified.

array typedef octet uniqueId[12];

typedef GraphicalObject GO[10][8]

Defines a type for a multi-dimensional

fixed-length sequence of elements of aspecified IDL type.

this figure continues on the next slide


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Figure 17.8IDL constructed types 2

Type Examples Use

record struct GraphicalObject {string type;Rectangle enclosing;boolean isFilled;

};

Defines a type for a record containing agroup of related entities. Structs arepassed by value in arguments andresults.

enumerated enum Rand(Exp, Number, Name);

The enumerated type in IDL maps atype name onto a small set of integervalues.

union union Exp switch (Rand) {case Exp: string vote;case Number: long n;case Name: string s;

The IDL discriminated union allowsone of a given set of types to be passedas an argument. The header isparameterized by anenum, whichspecifies which member is in use.};

age


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ageC RBA interoperable ob ect

referencesIOR formatIDL interface type nameProtocol and address details Object key

interface repositoryidentifier

IIOP host domainname

port number adapter name object name

gure


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gure .aming graph in C RBA

aming Serviceinitial naming context

ShapeList

CD E

B

initial naming context

P

R ST

V

Q U

initial naming context

XX


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.Part of the C RBA aming

Service amingContextinterface in IDL

struct NameComponent { string id; string kind; };

typedef sequence Name;

interface NamingContext {

void bind (in Name n, in Object obj);

binds the given name and remote object reference in my context.

void unbind (in Name n);

removes an existing binding with the given name.

void bind_new_context(in Name n);

creates a new naming context and binds it to a given name in my context.

Object resolve (in Name n);looks up the name in my context and returns its remote object reference.

void list (in unsigned long how_many, out BindingList bl, out BindingIterator bi)

returns the names in the bindings in my context.

};


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Figure 17.11C RBA event channels

consumersupplier

proxy consumer

notification

proxy supplier

event channel

notificationnotification

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