Introduction to CS739: Distribution Systems

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Introduction to CS739Distribution Systems
UNIVERSITY of WISCONSIN-MADISONComputer Sciences
Department
CS 739Distributed Systems
Andrea C. Arpaci-Dusseau
What are distributed systems? What are the
benefits and challenges? How will CS739 be
structured? Readings, Writeups,
Presentations Projects
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Goals of Course

• Learn about challenges and existing techniques
  for building distributed systems and services
• Read and discuss influential papers from SOSP,
  OSDI, NSDI
• Gain some experience programming in distributed
  environment
• Warm-up project
• Final project

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What is a Distributed System?

• Leslie Lamport says You know you have one when
  the crash of a computer you never heard of stops
  you from doing any work
• More technical definitionCollection of
  independent computers that appears to its users
  as a single coherent system
• How are parallel, distributed, networked systems
  different?
• All contain nodes (processing, memory, disk)
  connected with network

Moreunified
Lessunified
parallel
distributed
networked
Consider distributed services as well
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Benefits of Distributed Systems

• Great price/performance
• Leverage commodity components (nodes and
  networks)
• Use many, many of them
• Incremental scalability
• Can add x new nodes (or disks or memory) to
  improve performance x
• Improved availability
• Continue operating when some nodes stop working
• Improved reliability
• Deliver correct results when some nodes
  misbehave, corrupt data
• Allow geographically-distributed individuals to
  share data or cooperate

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Distributed System Challenges

• Lack of global state information
• Different nodes have different view of system
• What are the contents of file A?
• How many jobs are running on node X?
• Which nodes are currently part of the system?
• See delays, different ordering of messages, lost
  messages, network partitions
• Tension with goal of single coherent system
• Handling slow, failed and misbehaving nodes
• How do you avoid slow nodes?
• How do you get back data or work from failed
  node?
• When nodes disagree, how do you know who is
  wrong?
• Tension with goal of available and reliable
• When is it okay to have some centralized
  components?
• Simplifies state management, but single
  point-of-failure and performance bottleneck

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Content of 739

• Distributed system courses can be very different
• Theoretical distributed algorithms (e.g., to
  allow nodes to come to consensus or agreement)
• 4 lectures
• Practical distributed programming (e.g., using
  RPC, JAVA RMI, CORBA, DCOM, MPI, PVM)
• Warm-up project
• Research systems new ideas for making
  distributed systems better
• Focus of course
• Implemented systems with new conceptual ideas
• Recent papers in top systems conferences (SOSP,
  OSDI, NSDI)

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Learning by Reading

• Intense reading list assume sophisticated reader
  (736)
• Usually cover 1 fascinating paper per class
• No exams
• Three types of classes
• Formal lecture Only for 4 theory topics
• Discussions Most papers
• I ask questions, expect everyone to
  enthusiastically participate fairly casual
• Task 1 Read paper 2-3 times before class
• Task 2 Email write-up to me BEFORE class
• Task 3 Take turns being scribe (about 2 times in
  semester)
• Write-up notes from discussion in latex
• Post to web page within 72 hours

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Learning by Reading (cont)

• Types of classes (cont)
• Group-led lectures 4 topics
• Small group gives overview of about 3-4 related
  papers
• Topics
• Distributed system analysis
• Process migration
• Programming environments
• Specialized distributed services
• Advantages
• Good practice for giving presentations
• Learn about topic in slightly more depth
• Tasks
• Group
• Finalize related papers (1 week before)
• Present to me (2 days before)
• Use slides
• Everyone else Skim papers
• Handout State preferences by next week

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Course Topics Reading List

• Distributed Operating Systems (Survey, Amoeba vs
  Sprite)
• Network File Systems (NFS, Coda, LBFS)
• Theory Time, Ordering, and Distributed Snapshots
  (2 Lamport papers)
• Analysis of Distributed Systems (1 Group
  Presentation)
• Programming Environments (DSM, MapReduce, Group)
• Process Migration (1 Group)
• Specialized Distributed Services (Porcupine
  Group)
• SPRING BREAK
• Theory Consensus (Byzantine failures and
  fail-stop processors)
• Cluster-based File Systems (PetalFrangipani and
  GoogleFS)
• Communication Primitives (RPC vs U-Net)
• P2P Systems (Measurement, CFS, Amazon, Pangaea,
  LOCKSS)
• Miscellaneous Trust, Recovery, Mistakes,
  Speculation, Sensor Networks

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Learning by Doing

• Warm-up Project
• Goal Become familiar with existing distributed
  programming environments
• Examples Hadoop (open-source MapReduce), MPI,
  PVM
• Task 0 Get environment running
• Task 1 Implement simple application (e.g.,
  sorting)
• Task 2 Report sufficient numbers to indicate did
  something
• Final Project
• Goal 1 Experience with research process in
  general
• Work on open-ended project, unknown result
• New idea where dont know if it will work
• Goal 2 Learn about specific topic in depth
• Topic from my list or your own choice work with
  project partner
• Deliverables 20 minute talk, short research
  paper

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Agenda for Next Class

• See websitewww.cs.wisc.edu/cs739-1
• Read
• Survey Distributed Operating SystemsAndrew S.
  Tanenbaum and Robbert Van RenesseACM Computing
  Surveys, Volume 17, Issue 4 (December 1985), pp
  419-470
• Long paper Focus on Sections 1 and 2
• Answer question
• What were the goals of distributed systems at
  this time? Which design issue (I.e.,
  communication primitives, naming and protection,
  resource management, fault tolerance, services)
  seems most challenging (or interesting)? Why?
• Email answer to me with Subject cs739 Survey
• Think about group presentation papers