CS138:DistributedSystems

Staff• Faculty

– TheophilusBenson(AKATheo)

• HeadTAs

– SiddarthKaramcheti

• UTAs

– AmedeoFeliceAlberio– AbdullaAldilaijan

– ChristopherHarvie– BenjaminShteinfeld

– JaredSiskin

CourseDetails• CoursePolicies

• ClassWebsite:http://cs.brown.edu/courses/cs138/s18/index.html• Piazza:https://piazza.com/brown/spring2018/cs1380• Cheating/Collaboration

• Waitlist!!!!• Registered:~69• Waitlisted:~108• Attendclass!• Ifclassisrequiredforgraduation(2018),haveacademicadvisoremailus.

CourseDetails• CoursePolicies

• ClassWebsite:http://cs.brown.edu/courses/cs138/s18/index.html• Piazza:https://piazza.com/brown/spring2018/cs1380• Cheating/Collaboration

• Waitlist!!!!• Registered:~69• Waitlisted:~108• Attendclass!• Ifclassisrequiredforgraduation(2018),haveacademicadvisoremailus.

Workload

• Fourprograms(50%)– LiteMiner(10%)NEW!!!!!!

– Tapestry(13%)– Raft(13%)

– PuddleStore(13%)

• Fourwrittenhomeworks(15%)

• Onein-classmidtermexam(15%)

• Finalexam(20%)• Seehttp://cs.brown.edu/courses/cs138/s18/content/docs/syllabus.pdf

SkillsNeeded

• Abilitytowriteanddebuglargishprogramswiththreads– CS32or33

• Abilitytoproveatheorem– therewon’tbemany

– CS22ishelpful

• Willingnesstolearnanewprogramminglanguage– Go

Textbook

What Is A Distributed System?“Acollectionofindependentcomputersthatappearstoitsusersasasinglecoherentsystem.”

• Ideal:topresentasingle-systemimage:– Thedistributedsystem“lookslike”asinglecomputerratherthanacollectionofseparatecomputers.

DistributedSystemsareHardtoBuild

• Mustdealwithfailures

• Coordinationbetweennodes

• Consistencyandpersistence

• Concurrency

Google Confidential and Proprietary

OFC Bug History

WhyDoYouNeedADistributedSystem?

• Faulttolerance

• Scalability

• Performance

• Resourcesharing

• InformationGathering

Youwoulddesignadistributedsystemwhen…

• Interestedingettingfastandefficientdeeplearningframeworks

https://training.databricks.com/databricks_guide/gentle_introduction/spark_cluster_tasks.png

Youwoulddesignadistributedsystemwhen…

• Efficientlymanagingandcoordinatingbitcoinminers

https://medium.com/@lopp/the-future-of-bitcoin-mining-ac9c3dc39c60

Youwoulddesignadistributedsystemwhen…

• Designingsuccessfullargeonlineservices

http://www.ageofinnovation.org/gallery/the-benefits-of-using-online-services-pictures/The-benefits-of-using-online-services.jpg

Youwoulddesignadistributedsystemwhen…

• DesigningIoTplatforms

https://training.databricks.com/databricks_guide/gentle_introduction/spark_cluster_tasks.png

Youwoulddesignadistributedsystemwhen…

• Designingselfdrivingcars

https://training.databricks.com/databricks_guide/gentle_introduction/spark_cluster_tasks.png

Youwoulddesignadistributedsystemwhen…

• Designingtradingplatforms

https://3nlm2c1gjj0z2ju16293909h-wpengine.netdna-ssl.com/wp-content/uploads/2017/01/best-stock-trading-software-mac-

WhyDoYouNeedADistributedSystem?

• Buildingacloud

• ScalingoutthenextAirBnB

• Designingaselfdrivingcar

• Interestedingettingfastandefficientdeeplearningframeworks

• Developingthenextgameframework

• Designingatradingplatformforahedgefundorinvestmentbank

CaseStudy:Facebook

CAVA

• Circa2007,Facebookdecidedtoaddaseconddatacentertoitsoperations

FacebookDatabaseReplication

https://www.facebook.com/notes/facebook-engineering/scaling-out/23844338919

Why?

• Majorreason:latency– can’tgofasterthanthespeedoflightyet

• Otherreasons– scale:needtohandlerapidlyincreasingloads– resiliency:whatifanearthquakehitsCA?– power:sometimesavailabilityofpowerlimitsthesizeofadatacenter!

Cachingobjects

• Facebookhandlesreadsviamemcached

Cachingobjects

• Cacheinvalidatedonanewwrite

AddinganewDatacenter

• Initialdesignhadabug

AddinganewDatacenter

Introduction to Go

Where is Go used?

● Google, of course! ● Docker (Container management) ● CloudFlare (Content Delivery Network) ● Digital Ocean (VM hosting) ● Dropbox (Cloud storage/file sharing) ● … and many more!

Why use Go?

● Easy concurrency w/ goroutines (green threads)

● Garbage collection and memory safety

● Libraries provide easy RPC

● Channels for communication between goroutines

Example: Simple Program

packagemain

import( "fmt" "os")

funcmain(){ forcount:=1;count<100;count++{ ifcount%2==0{ fmt.Printf("Foundevennumber:%v\n",count) }else{ fmt.Fprintf(os.Stderr,"Notanevennumber:%v\n",count) } }}

● No parentheses

● “for { }” will loop forever

● “for condition { }” avoids initialization/afterthought, similar to a while loop

Learning Go

● Project 0: Whatsup? ● Effective Go ● golang.org/doc ● tour.golang.org ● go-handout.pdf

PuddleStore

• Averydistributedfilesystem– thousandsofcomputers

• allovertheworld– (oratleastthroughouttheSunLab)

• nocommonadministration

– eachholdspiecesofafewfiles

• piecesreplicatedonmanycomputers

• BasedonOceanStore– anditsPondprototype

AFile

Indirect Block

Data Block 1 Data Block 4

Data Block 2 Data Block 3

ADistributedFile

Indirect Block

Data Block 1

Data Block 4

Data Block 2Data Block 3

Indirect Block

Indirect Block

Indirect Block

Data Block 1

Data Block 1

Data Block 1

Data Block 2

Data Block 2

Data Block 2

Data Block 1

Data Block 1

Data Block 1

Data Block 1

Data Block 2

Data Block 2

Data Block 2

HowDoYouFindthePieces?

• Hashing• But...

– nodesmaycrash

• duplicatesarerequired

• howdoyoufindthem?

– mustprovidegoodperformance

• cachingmaybenecessary

• piecesmayhavetobereassignedtootherlocations

MakingItWork(sortof…)• Assigneachblockauniquen-bitID

– cryptohashofitscontents• Assigneachcomputerauniquen-bitID

• StoreblockatcomputerthathasclosestID

• Routerequestsforthatblocktothatcomputer

0x2a74ca56 0x9da6f453

0x529e02f80xd53b7621

Data Block 10x87a6df52

I want Block 1

OverlayNetworks

MakingIt(really)Work(withhighprobability)• Assigneachblockauniquen-bitID

– cryptohashofitscontents• Assigneachcomputerauniquen-bitID

• Storemultiplecopiesofblockseachatanumberofcomputers

• StoreblockaddressesatcomputerthathasclosestID– addressesarecachedatothernodes

• Routerequestsforthatblocktothatcomputer– requestisredirectedtonearestcomputerthathascopyofblock

0x2a74ca56 0x9da6f453

0x529e02f80xd53b7621

Data Block 10x87a6df52

0x87a6df52 locations: 0x2a74ca56 0xd53b7621

Data Block 10x87a6df52

I want Block 1

PublishingD A

B

C

R ABC

A

A

A

A A

A

B

B

B

B

B BC C

C

C C

?

Tapestry

• Distributedobjectlocationandrouting(DOLR)– youimplementitinthesecondprogrammingassignment

MorePuddleStoreIssues

• Howarefilesnamed?– fileID=CryptoHash(filename)

• Howarefilesupdated?– carefully…

CopyonWrite(1)

Indirect Block

Data Block 1 Data Block 4

Data Block 2 Data Block 3

Version Node

fileID

ModifiedData Block 4

Indirect Block

ModifiedData Block 3

CopyonWrite(2)

Indirect Block

Data Block 1 Data Block 4

Data Block 2 Data Block 3

Version Node

fileID

ModifiedData Block 4

Indirect Block

ModifiedData Block 3

MoreRedundancy

Indirect Block

Data Block 1 Data Block 4

Data Block 2 Data Block 3

fileID

ModifiedData Block 4

Indirect Block

ModifiedData Block 3

Version Node

Raft

• Multipleclientsupdatefileconcurrently• Eachcommunicateswithdifferentservers

– serverspropagatechangestoallcopies

• Howdoweensurethatallcopiesareupdatedinthesameorder?– ordermatters...

• Raft– thirdprogrammingassignment

FinalPuddleStore

• Youputallthistogether– wegiveyoutheBdesign

• ifyouimplementitcompletely:yougetaB

– ifyouimproveit(reasonablywell):yougetanA(anditmaycountasacapstone)

• you’reencouragedtodiscussyourdesignwithclassmates

Top Secret

Announcements

• CS138Social• Where:CIT3rdFloorAtrium• When:6-8pm• What:MeetTAs

• Filloutandsigncheatingpolicy• TAwillsendthisouttonight

• Project1outtonight• Writeaminerandminingpoolmanager• Due:Feb13