h1. Wukong
Wukong is Ruby for Hadoop -- it makes "Hadoop":http://hadoop.apache.org/core so easy a chimpanzee can use it.
Treat your dataset like a
* stream of lines when it's efficient to process by lines
* stream of field arrays when it's efficient to deal directly with fields
* stream of lightweight objects when it's efficient to deal with objects
Wukong is friends with "Hadoop":http://hadoop.apache.org/core the elephant, "Pig":http://hadoop.apache.org/pig/ the query language, and the @cat@ on your command line.
The **main documentation** lives on the "Wukong Pages.":http://mrflip.github.com/wukong Please feel free to add supplemental information to the "wukong wiki.":http://wiki.github.com/mrflip/wukong
* "Install and set up wukong":http://mrflip.github.com/wukong/INSTALL.html
* "Tutorial":http://mrflip.github.com/wukong/tutorial.html
* "Usage notes":http://mrflip.github.com/wukong/usage.html
* "Wutils":http://mrflip.github.com/wukong/wutils.html -- command-line utilies for working with data from the command line
* Links and tips for "configuring and working with hadoop":http://mrflip.github.com/wukong/hadoop-tips.html
* Wukong is licensed under the "Apache License":http://mrflip.github.com/wukong/LICENSE.html (same as Hadoop)
* "More info":http://mrflip.github.com/wukong/moreinfo.html
h2. Help!
Send Wukong questions to the "Infinite Monkeywrench mailing list":http://groups.google.com/group/infochimps-code
h2. Install
** "Main Install and Setup Documentation":http://mrflip.github.com/wukong/INSTALL.html **
h3. Get the code
We're still actively developing wukong. The newest version is available via "Git":http://git-scm.com on "github:":http://github.com/mrflip/wukong
pre. $ git clone git://github.com/mrflip/wukong
A gem is available from "gemcutter:":http://gemcutter.org/gems/wukong
pre. $ sudo gem install wukong --source=http://gemcutter.org
(don't use the gems.github.com version -- it's way out of date.)
You can instead download this project in either "zip":http://github.com/mrflip/wukong/zipball/master or "tar":http://github.com/mrflip/wukong/tarball/master formats.
h3. Dependencies and setup
To finish setting up, see the "detailed setup instructions":http://mrflip.github.com/wukong/INSTALL.html and then read the "usage notes":http://mrflip.github.com/wukong/usage.html
h2. How to write a Wukong script
** "Tutorial By Example":http://mrflip.github.com/wukong/tutorial.html **
Here's a script to count words in a text stream:
<pre><code> require 'wukong'
module WordCount
class Mapper < Wukong::Streamer::LineStreamer
# Emit each word in the line.
def process line
words = line.strip.split(/\W+/).reject(&:blank?)
words.each{|word| yield [word, 1] }
end
end
class Reducer < Wukong::Streamer::ListReducer
def finalize
yield [ key, values.map(&:last).map(&:to_i).sum ]
end
end
end
Wukong::Script.new(
WordCount::Mapper,
WordCount::Reducer
).run # Execute the script
</code></pre>
The first class, the Mapper, eats lines and craps @[word, count]@ records: word is the /key/, its count is the /value/.
In the reducer, the values for each key are stacked up into a list; then the record(s) yielded by @#finalize@ are emitted. There are many other ways to write the reducer (most of them are better) -- see the ["examples":examples/]
h3. Structured data stream
You can also use structs to treat your dataset as a stream of objects:
<pre><code> require 'wukong'
require 'my_blog' #defines the blog models
# structs for our input objects
Tweet = Struct.new( :id, :created_at, :twitter_user_id,
:in_reply_to_user_id, :in_reply_to_status_id, :text )
TwitterUser = Struct.new( :id, :username, :fullname,
:homepage, :location, :description )
module TwitBlog
class Mapper < Wukong::Streamer::RecordStreamer
# Watch for tweets by me
MY_USER_ID = 24601
#
# If this is a tweet is by me, convert it to a Post.
#
# If it is a tweet not by me, convert it to a Comment that
# will be paired with the correct Post.
#
# If it is a TwitterUser, convert it to a User record and
# a user_location record
#
def process record
case record
when TwitterUser
user = MyBlog::User.new.merge(record) # grab the fields in common
user_loc = MyBlog::UserLoc.new(record.id, record.location, nil, nil)
yield user
yield user_loc
when Tweet
if record.twitter_user_id == MY_USER_ID
post = MyBlog::Post.new.merge record
post.link = "http://twitter.com/statuses/show/#{record.id}"
post.body = record.text
post.title = record.text[0..65] + "..."
yield post
else
comment = MyBlog::Comment.new.merge record
comment.body = record.text
comment.post_id = record.in_reply_to_status_id
yield comment
end
end
end
end
end
Wukong::Script.new( TwitBlog::Mapper, nil ).run # identity reducer
</code></pre>
h3. Advanced Patterns
Wukong has a good collection of map/reduce patterns. Here's an AccumulatingReducer that takes a long list of key-value pairs and emits, for each key, all its corresponding values in one line.
<pre><code> #
# Roll up all values for each key into a single line
#
class GroupByReducer < Wukong::Streamer::AccumulatingReducer
attr_accessor :values
# Start with an empty list
def start! *args
self.values = []
end
# Aggregate each value in turn
def accumulate key, value
self.values << value
end
# Emit the key and all values, tab-separated
def finalize
yield [key, values].flatten
end
end
</code></pre>
So given adjacency pairs for the following directed friend graph:
<pre><code>
@jerry @elaine
@elaine @jerry
@jerry @kramer
@kramer @jerry
@kramer @bobsacamato
@kramer @newman
@jerry @superman
@newman @kramer
@newman @elaine
@newman @jerry
</code></pre>
You'd end up with
<pre><code>
@elaine @jerry
@jerry @elaine @kramer @superman
@kramer @bobsacamato @jerry @newman
@newman @elaine @jerry @kramer
</code></pre>
h2. Gotchas
h4. RecordStreamer dies on blank lines with "wrong number of arguments"
If your lines don't always have a full complement of fields, and you define #process() to take fixed named arguments, then ruby will complain when some of them don't show up:
<pre>
class MyUnhappyMapper < Wukong::Streamer::RecordStreamer
# this will fail if the line has more or fewer than 3 fields:
def process x, y, z
p [x, y, z]
end
end
</pre>
The cleanest way I know to fix this is with recordize, which you should recall always returns an array of fields:
<pre>
class MyHappyMapper < Wukong::Streamer::RecordStreamer
# extracts three fields always; any missing fields are nil, any extra fields discarded
# @example
# recordize("a") # ["a", nil, nil]
# recordize("a\t\b\tc") # ["a", "b", "c"]
# recordize("a\t\b\tc\td") # ["a", "b", "c"]
def recordize raw_record
x, y, z = super(raw_record)
[x, y, z]
end
# Now all lines produce exactly three args
def process x, y, z
p [x, y, z]
end
end
</pre>
If you want to preserve any extra fields, use the extra argument to #split():
<pre>
class MyMoreThanHappyMapper < Wukong::Streamer::RecordStreamer
# extracts three fields always; any missing fields are nil, the final field will contain a tab-separated string of all trailing fields
# @example
# recordize("a") # ["a", nil, nil]
# recordize("a\t\b\tc") # ["a", "b", "c"]
# recordize("a\t\b\tc\td") # ["a", "b", "c\td"]
def recordize raw_record
x, y, z = split(raw_record, "\t", 3)
[x, y, z]
end
# Now all lines produce exactly three args
def process x, y, z
p [x, y, z]
end
end
</pre>
h2. Why is it called Wukong?
Hadoop, as you may know, is "named after a stuffed elephant.":http://en.wikipedia.org/wiki/Hadoop Since Wukong was started by the "infochimps":http://infochimps.org team, we needed a simian analog. A Monkey King who journeyed to the land of the Elephant seems to fit the bill:
bq. Sun Wukong (孙悟空), known in the West as the Monkey King, is the main character in the classical Chinese epic novel Journey to the West. In the novel, he accompanies the monk Xuanzang on the journey to retrieve Buddhist sutras from India.
bq. Sun Wukong possesses incredible strength, being able to lift his 13,500 jīn (8,100 kg) Ruyi Jingu Bang with ease. He also has superb speed, traveling 108,000 li (54,000 kilometers) in one somersault. Sun knows 72 transformations, which allows him to transform into various animals and objects; he is, however, shown with slight problems transforming into other people, since he is unable to complete the transformation of his tail. He is a skilled fighter, capable of holding his own against the best generals of heaven. Each of his hairs possesses magical properties, and is capable of transforming into a clone of the Monkey King himself, or various weapons, animals, and other objects. He also knows various spells in order to command wind, part water, conjure protective circles against demons, freeze humans, demons, and gods alike. -- ["Sun Wukong's Wikipedia entry":http://en.wikipedia.org/wiki/Wukong]
The "Jaime Hewlett / Damon Albarn short":http://news.bbc.co.uk/sport1/hi/olympics/monkey that the BBC made for their 2008 Olympics coverage gives the general idea.
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h2. More info
There are many useful examples in the examples/ directory.
h3. Credits
Monkeyshines was written by "Philip (flip) Kromer":http://mrflip.com (flip@infochimps.org / "@mrflip":http://twitter.com/mrflip) for the "infochimps project":http://infochimps.org
Patches submitted by:
* gemified by Ben Woosley (ben.woosley with the gmails)
* ruby interpreter path fix by "Yuichiro MASUI":http://github.com/masuidrive - masui at masuidrive.jp - http://blog.masuidrive.jp/
Thanks to:
* "Fredrik Möllerstrand (@lenbust)":http://twitter.com/lenbust for the examples/contrib/jeans working example
* "Brad Heintz":http://www.bradheintz.com/no1thing/talks/ for his early feedback
* "Phil Ripperger":http://blog.pdatasolutions.com for his "wukong in the Amazon AWS cloud":http://blog.pdatasolutions.com/post/191978092/ruby-on-hadoop-quickstart tutorial.
h3. Help!
Send monkeyshines questions to the "Infinite Monkeywrench mailing list":http://groups.google.com/group/infochimps-code
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