This document provides an introduction to cloud computing and parallel/distributed processing through a lecture on the topic. It discusses web-scale problems involving large amounts of data, the trend toward large centralized data centers, and different computing models like utility computing. It also introduces concepts like virtualization, MapReduce, and designing highly interactive web applications. The lecture covers challenges in parallelization like assigning work and synchronizing workers. It provides examples of patterns for parallelism like master/slave and producer/consumer models.

1. Cloud Computing Lecture #1
What is Cloud Computing?
(and an intro to parallel/distributed processing)
Jimmy Lin
The iSchool
University of Maryland
Wednesday, September 3, 2008
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States
See http://creativecommons.org/licenses/by-nc-sa/3.0/us/ for details
Some material adapted from slides by Christophe Bisciglia, Aaron Kimball, & Sierra Michels-Slettvet,
Google Distributed Computing Seminar, 2007 (licensed under Creation Commons Attribution 3.0 License)

2. Source: http://www.free-pictures-photos.com/

3. The iSchool
University of Maryland
What is Cloud Computing?
1. Web-scale problems
2. Large data centers
3. Different models of computing
4. Highly-interactive Web applications

4. The iSchool
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1. Web-Scale Problems
 Characteristics:
 Definitely data-intensive
 May also be processing intensive
 Examples:
 Crawling, indexing, searching, mining the Web
 “Post-genomics” life sciences research
 Other scientific data (physics, astronomers, etc.)
 Sensor networks
 Web 2.0 applications
 …

5. The iSchool
University of Maryland
How much data?
 Wayback Machine has 2 PB + 20 TB/month (2006)
 Google processes 20 PB a day (2008)
 “all words ever spoken by human beings” ~ 5 EB
 NOAA has ~1 PB climate data (2007)
 CERN’s LHC will generate 15 PB a year (2008)
640K ought to be
enough for anybody.

6. Maximilien Brice, © CERN

7. Maximilien Brice, © CERN

8. The iSchool
University of Maryland
There’s nothing like more data!
s/inspiration/data/g;
(Banko and Brill, ACL 2001)
(Brants et al., EMNLP 2007)

9. The iSchool
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What to do with more data?
 Answering factoid questions
 Pattern matching on the Web
 Works amazingly well
 Learning relations
 Start with seed instances
 Search for patterns on the Web
 Using patterns to find more instances
Who shot Abraham Lincoln? → X shot Abraham Lincoln
Birthday-of(Mozart, 1756)
Birthday-of(Einstein, 1879)
Wolfgang Amadeus Mozart (1756 - 1791)
Einstein was born in 1879
PERSON (DATE –
PERSON was born in DATE
(Brill et al., TREC 2001; Lin, ACM TOIS 2007)
(Agichtein and Gravano, DL 2000; Ravichandran and Hovy, ACL 2002; … )

10. The iSchool
University of Maryland
2. Large Data Centers
 Web-scale problems? Throw more machines at it!
 Clear trend: centralization of computing resources in large
data centers
 Necessary ingredients: fiber, juice, and space
 What do Oregon, Iceland, and abandoned mines have in
common?
 Important Issues:
 Redundancy
 Efficiency
 Utilization
 Management

11. Source: Harper’s (Feb, 2008)

12. Maximilien Brice, © CERN

13. The iSchool
University of Maryland
Key Technology: Virtualization
Hardware
Operating System
App App App
Traditional Stack
Hardware
OS
App App App
Hypervisor
OS OS
Virtualized Stack

14. The iSchool
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3. Different Computing Models
 Utility computing
 Why buy machines when you can rent cycles?
 Examples: Amazon’s EC2, GoGrid, AppNexus
 Platform as a Service (PaaS)
 Give me nice API and take care of the implementation
 Example: Google App Engine
 Software as a Service (SaaS)
 Just run it for me!
 Example: Gmail
“Why do it yourself if you can pay someone to do it for you?”

15. The iSchool
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4. Web Applications
 A mistake on top of a hack built on sand held together by
duct tape?
 What is the nature of software applications?
 From the desktop to the browser
 SaaS == Web-based applications
 Examples: Google Maps, Facebook
 How do we deliver highly-interactive Web-based
applications?
 AJAX (asynchronous JavaScript and XML)
 For better, or for worse…

16. The iSchool
University of Maryland
What is the course about?
 MapReduce: the “back-end” of cloud computing
 Batch-oriented processing of large datasets
 Ajax: the “front-end” of cloud computing
 Highly-interactive Web-based applications
 Computing “in the clouds”
 Amazon’s EC2/S3 as an example of utility computing

17. The iSchool
University of Maryland
Amazon Web Services
 Elastic Compute Cloud (EC2)
 Rent computing resources by the hour
 Basic unit of accounting = instance-hour
 Additional costs for bandwidth
 Simple Storage Service (S3)
 Persistent storage
 Charge by the GB/month
 Additional costs for bandwidth
 You’ll be using EC2/S3 for course assignments!

18. The iSchool
University of Maryland
This course is not for you…
 If you’re not genuinely interested in the topic
 If you’re not ready to do a lot of programming
 If you’re not open to thinking about computing in new ways
 If you can’t cope with uncertainly, unpredictability, poor
documentation, and immature software
 If you can’t put in the time
Otherwise, this will be a richly rewarding course!

19. Source: http://davidzinger.wordpress.com/2007/05/page/2/

20. The iSchool
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Cloud Computing Zen
 Don’t get frustrated (take a deep breath)…
 This is bleeding edge technology
 Those W$*#T@F! moments
 Be patient…
 This is the second first time I’ve taught this course
 Be flexible…
 There will be unanticipated issues along the way
 Be constructive…
 Tell me how I can make everyone’s experience better

21. Source: Wikipedia

22. Source: Wikipedia

23. Source: Wikipedia

24. Source: Wikipedia

25. The iSchool
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Things to go over…
 Course schedule
 Assignments and deliverables
 Amazon EC2/S3

26. The iSchool
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Web-Scale Problems?
 Don’t hold your breath:
 Biocomputing
 Nanocomputing
 Quantum computing
 …
 It all boils down to…
 Divide-and-conquer
 Throwing more hardware at the problem
Simple to understand… a lifetime to master…

27. The iSchool
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Divide and Conquer
“Work”
w1 w2 w3
r1 r2 r3
“Result”
“worker” “worker” “worker”
Partition
Combine

28. The iSchool
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Different Workers
 Different threads in the same core
 Different cores in the same CPU
 Different CPUs in a multi-processor system
 Different machines in a distributed system

29. The iSchool
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Choices, Choices, Choices
 Commodity vs. “exotic” hardware
 Number of machines vs. processor vs. cores
 Bandwidth of memory vs. disk vs. network
 Different programming models

30. The iSchool
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Flynn’s Taxonomy
Instructions
Single (SI) Multiple (MI)
Data
Multiple(M
SISD
Single-threaded
process
MISD
Pipeline
architecture
SIMD
Vector Processing
MIMD
Multi-threaded
Programming
Single(SD)

31. The iSchool
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SISD
D D D D D D D
Processor
Instructions

32. The iSchool
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SIMD
D0
Processor
Instructions
D0D0 D0 D0 D0
D1
D2
D3
D4
…
Dn
D1
D2
D3
D4
…
Dn
D1
D2
D3
D4
…
Dn
D1
D2
D3
D4
…
Dn
D1
D2
D3
D4
…
Dn
D1
D2
D3
D4
…
Dn
D1
D2
D3
D4
…
Dn
D0

33. The iSchool
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MIMD
D D D D D D D
Processor
Instructions
D D D D D D D
Processor
Instructions

34. The iSchool
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Memory Typology: Shared
Memory
Processor
Processor Processor
Processor

35. The iSchool
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Memory Typology: Distributed
MemoryProcessor MemoryProcessor
MemoryProcessor MemoryProcessor
Network

36. The iSchool
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Memory Typology: Hybrid
Memory
Processor
Network
Processor
Memory
Processor
Processor
Memory
Processor
Processor
Memory
Processor
Processor

37. The iSchool
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Parallelization Problems
 How do we assign work units to workers?
 What if we have more work units than workers?
 What if workers need to share partial results?
 How do we aggregate partial results?
 How do we know all the workers have finished?
 What if workers die?
What is the common theme of all of these problems?

38. The iSchool
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General Theme?
 Parallelization problems arise from:
 Communication between workers
 Access to shared resources (e.g., data)
 Thus, we need a synchronization system!
 This is tricky:
 Finding bugs is hard
 Solving bugs is even harder

39. The iSchool
University of Maryland
Managing Multiple Workers
 Difficult because
 (Often) don’t know the order in which workers run
 (Often) don’t know where the workers are running
 (Often) don’t know when workers interrupt each other
 Thus, we need:
 Semaphores (lock, unlock)
 Conditional variables (wait, notify, broadcast)
 Barriers
 Still, lots of problems:
 Deadlock, livelock, race conditions, ...
 Moral of the story: be careful!
 Even trickier if the workers are on different machines

40. The iSchool
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Patterns for Parallelism
 Parallel computing has been around for decades
 Here are some “design patterns” …

41. The iSchool
University of Maryland
Master/Slaves
slaves
master

42. The iSchool
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Producer/Consumer Flow
CP
P
P
C
C
CP
P
P
C
C

43. The iSchool
University of Maryland
Work Queues
CP
P
P
C
C
shared queue
W W W W W

44. The iSchool
University of Maryland
Rubber Meets Road
 From patterns to implementation:
 pthreads, OpenMP for multi-threaded programming
 MPI for clustering computing
 …
 The reality:
 Lots of one-off solutions, custom code
 Write you own dedicated library, then program with it
 Burden on the programmer to explicitly manage everything
 MapReduce to the rescue!
 (for next time)