Self-* Systems CSE 598B

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Self- SystemsCSE 598B

• Instructor Bhuvan Urgaonkar
• Fall 2005

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Introduction

• Bhuvan Urgaonkar
• Assistant Professor, CSE
• Ph.D. Univ. of Mass., Amherst
• Research Interests
• Distributed systems, operating systems, computer
  networking, modeling of systems
• Office 338D, Email bhuvan_at_cse.psu.edu
• Office hours and class timings
• Undecided as of now, we will figure this out at
  the end of the class
• If in doubt just walk in anytime!
• Students turn to introduce themselves

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Self- systems

• Self- a regular expression
• But not quite
• No self-destroying systems ?
• Three themes
• Self-tuning systems
• Self-healing systems
• Self-stabilizing systems
• Course Web page
• http//www.cse.psu.edu/bhuvan/teaching/fall05/sel
  f-star.html
• To do Set up a course mailing list

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Self-tuning systems

• Systems that can adapt their behavior to
  dynamically changing external influences on their
  own

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Internet applications

• Proliferation of Internet applications

auction site
online game
online retail store

• Growing significance in personal, business
  affairs
• Focus Internet server applications

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Hosting platforms

• Data Centers
• Clusters of servers
• Storage devices
• High-speed interconnect
• Hosting platforms
• Rent resources to third-party applications
• Performance guarantees in return for revenue
• Benefits
• Applications dont need to maintain their own
  infrastructure
• Rent server resources, possibly on demand
• Platform provider generates revenue by renting
  resources

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Goals of a hosting platform

• Meet service-level agreements
• Satisfy application performance guarantees
• E.g., average response time, throughput
• Maximize revenue
• E.g., maximize the number of hosted applications
• Question How should a hosting platform manage
  its resources to meet these goals?

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Challenge dynamic workloads
1200

• Multi-time-scale variations
• Time-of-day, hour-of-day
• Overloads
• E.g., Flash crowds
• User threshold for
  response time
  8-10 s
• Key issue How to provide good
• response time under varying workloads?

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Time (days)
Arrivals per min
140K
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Time (hours)
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Self-tuning systems

• A self-tuning hosting platform

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Dynamic provisioning
Monitor workload
Compute current/ future demand
Adjust allocation

• Key idea increase or decrease allocated servers
  to handle workload fluctuations
• Monitor incoming workload
• Compute current or future demand
• Match number of allocated servers to demand

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Dynamic provisioning at multiple time-scales

• Predictive provisioning
• Certain Internet workloads patterns can be
  predicted
• E.g., time-of-day effects, increased workload
  during Thanksgiving
• Design a good application model
• Provision using model at time-scale of hours or
  days
• Reactive provisioning
• Applications may see unpredictable fluctuations
• E.g., Increased workload to news-sites after an
  earthquake
• Detect such anomalies and react fast (minutes)
• Question How to put these together?
• When to invoke the predictor and the reactor?

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Self-healing systems

• Systems that continue to operate on their own
  despite faults or failures
• Distinction between faults and failures
• Fault A sysadmin sets a small concurrency limit
  for a Web server
• Failure debris from an external fuel tank is
  thought to have struck Columbia's left wing in
  2003.
• Failure/fault handling capability built into the
  system
• Graceful degradation
• We will study classic literature in fault
  tolerance, papers that apply these principles to
  modern distributed systems

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Self-stabilizing systems

• Guaranteed to converge to a desired behavior from
  any initial state if left alone
• Why should one have interest in self-stabilizing
  algorithms?
• Its applicability to distributed systems
• Recovering from faults of a space shuttle. Faults
  may cause malfunction for a while. Using a
  self-stabilizing algorithm for its control will
  cause an automatic recovery, and enables the
  shuttle continue in its task

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What is a self-stabilizing algorithm?

• This question will be answered using the
  Stabilizing Orchestra example
• The Problem
• The conductor is unable to participate harmony
  is achieved by players listening to their
  neighbor players
• Windy evening the wind can turn some pages in
  the score, and the players may not notice the
  change

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The Stabilizing Orchestra Example

• Our Goal
• To guarantee that harmony is achieved at some
  point following the last undesired page turn
• Imagine that the drummer notices a different page
  of the violin next to him (solutions and their
  problems)
• The drummer turns to its neighbors new page
  what if the violin player noticed the difference
  as well?
• Both the drummer and violin player start from the
  beginning- what if the player next to the violin
  player notices the change only after sync between
  the other 2?

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The Self-Stabilizing Solution

• Every player will join the neighboring player who
  is playing the earliest page (including himself)

• Note that the score has a bounded length. What
  happens if a player goes to the first page of the
  score before harmony is achieved?
• In every long enough period in which the wind
  does not turn a page, the orchestra resumes
  playing in synchrony

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Discussion Overlaps and distinctions

• Self-tuning vs self-healing vs self-stabilizing
  systems
• Proactive vs reactive

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Crosscutting goals and challenges

• Removing costly and error-prone humans from
  administering complex systems
• Learning from the past
• Modeling systems to render them amenable to
  analysis
• Understanding how robust a system is
• Robust predictable behavior, graceful
  degradation
• Equivalent Figuring out how to make a system
  robust

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Introspection!

• Everyone gives an example of a self- aspect from
  their research/experience
• Arjun e-commerce applications
• Amitayu dynamic allocation of servers in a farm
• Ross Rosss sensor n/w
• Huajing information ret/ feedback
• Young fault handling by duplication
• Krishna activity migration in a multiprocessor

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Goals of the course

• Understand classic literature
• Identify theory and systems issues/tools common
  across these diverse domains
• Statistical learning, control theory, measurement
  techniques, data analysis, fault tolerance,
  modeling
• I will try to have some guest lectures
• Learn to appreciate how theory translates into
  and compares with practice
• Critically evaluate papers and present them, use
  these in research

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Some administrative details
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Grading policy

• Paper presentations 30
• Class participation and discussion 15
• Lets have lots of heated discussions
• Dont be shy!
• Paper evaluations due before class 15
• A conference-style evaluation form
• Semester-long project 30
• May be replaced by a term paper
• Apply ideas to your research, masters thesis
• Final exam 10
• Take-home exam

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Expected course-load

• No intentions of stressing you out!
• Round-robin presentation policy
• Number of presentations will depend on how many
  students enroll
• Red-teams To make sure you come prepared
• We DONT want bad presentations!
• Mid-term and final presentations for students
  doing projects
• End-of-semester take-home exam
• Goal Find out what we learnt in the course

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Presentations

• Prepare about 45-min long talk
• Rest of the class for discussions
• We will accept or reject papers at the end of
  each class ?
• Red team
• Each presenter will practice his/her talk with
  the assigned red team before the class
• You are welcome to talk to me, discuss slides,
  ask for help understanding the paper before
  presenting it
• Use the powerpoint template on course page
• We will try to become good speakers and reviewers!

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Paper evaluations

• Due the midnight before the class
• I will put up an evaluation format that you will
  adhere to
• No long essays needed
• Be critical, read the papers carefully
• I will anonymize evaluations and put them up
  after the class so all can read them
• Acceptable txt, pdf

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Course project

• Not compulsory
• You may work in groups of up to 2 students
• You may replace it with a term paper
• Survey of additional reading material
• Project may be
• A theoretical exercise
• Implementation-based
• A thought experiment
• Report and term papers due at the end of the
  semester

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Final exam

• Day-long take-home exam
• For students doing projects, I will design
  questions related to their project
• For students doing a survey, I will design
  questions based on their survey report

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Miscelleneous

• Please register soon so the course can be offered
• At least 5 students need to take the course
• Lets figure out course timings suitable to all
• Random thoughts
• Would you like to solve puzzles?
• Would you like to have discussions on systems
  research in general, hot areas, top conferences
  ?
• Would you like to take turns as scribes?
• Hope We will learn a lot and have lots of fun in
  this course

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Questions or comments?