Discussion Class 8

1
Discussion Class 8

• Map/Reduce Programming

2
Discussion Classes
Format Question Ask a member of the class to
answer. Provide opportunity for others to
comment. When answering Stand up. Give your
name. Make sure that the TA hears it. Speak
clearly so that all the class can
hear. Suggestions Do not be shy at presenting
partial answers. Differing viewpoints are
welcome.
3
Question 1 Purpose

• What is the social and economic reason that
  companies such as Google use novel programming
  methods such as Map/Reduce?
• How successful does it appear to be?

4
Question 2 Types
Explain the following Conceptually the map and
reduce functions supplied by the user have
associated types map (k1,v1) -gt
list(k2,v2) reduce (k2,list(v2)) -gt
list(v2) The output from Map is different from
the input to Reduce. What happens in between?
5
Question 3 Example
Explain the following pseudo-code
map(String key, String value) // key
document name // value document contents
for each word w in value
EmitIntermediate(w, "1") reduce(String key,
Iterator values) // key a word // values
a list of counts int result 0 for each v
in values result ParseInt(v)
Emit(AsString(result))
6
Question 4 Implementation
7
Question 5 Reliability and Performance
What happens if a worker computer fails? What
happens if the master fails? Explain the
function of backup tasks.