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README.md

README.md

Hadoop MR Utils

What is this?

This is a collection of my helper scripts for running jobs on Elastic MapReduce and example code to get started with Hadoop streaming and Pig jobs. I put all these together for a workshop at Noisebridge's Machine Learning meetup, so they're rather Noisebridge-specific at times.

This might turn into a curated repository of generally useful and/or interesting examples some day. In the meantime, though, it's all ad hoc and slapped together.

Feel free to use and repurpose all this code for whatever you want. The Elastic MapReduce scripts in particular are very useful if you're using AWS.

What's in here?

  • emr/ contains a bunch of helper scripts to spin up clusters, deploy code to S3, and run jobs on Elastic MapReduce.
  • scripts/ contains a bunch of example code to demonstrate writing jobs using Hadoop streaming and Pig.

AWS/EMR Setup

Setup instructions for AWS and Elastic MapReduce are in `emr/setup-instructions/.

Hadoop Setup

If you want to set up Hadoop locally (not necessary to understand or run these examples on Elastic MapReduce), I'd suggest using Cloudera's RPM and deb packages on a RedHat or Debian-based Linux distribution. It'll save you enormous hassle.

Pig Setup

It'll be useful to set up Pig version 0.6 or less to run and test your Pig code locally over smaller samples of your data. Pig 0.7 onwards requires Hadoop to run locally. While there are known discrepancies between running Pig version <= 0.6 in local mode and on a Hadoop cluster, they aren't likely to crop up in these examples and it'll be much, much simpler to get started.

Download Pig 0.6 from here: http://hadoop.apache.org/pig/releases.html (click on "Download a release now!" and pick one of the mirrors).

Extract the contents somewhere (mine are in /home/voberoi/pig) and add the following to your ~/.bash_rc or ~/.bash_profile:

export PATH=/home/voberoi/pig/bin:$PATH

You'll also need to set the JAVA_HOME variable. Google around to figure out what your JAVA_HOME is and add the following to your ~/.bash_rc or ~/bash_profile:

export JAVA_HOME=/path/to/java/home

When you want to run a Pig program locally, always include -x local as an argument. For example:

pig -x local -param INPUT=/some/data -param OUTPUT=/output/data myscript.pig

Hadoop Streaming

Hadoop allows you to write your mappers and reducers in any language. Your mappers and reducers must read input on STDIN and write to STDOUT. Check out the word-count Python examples in scripts/word-count.

The nice thing about this is that it's remarkably easy to test locally without setting up a Hadoop cluster. To 'simulate MapReduce' all you need to do is this:

cat data | my_mapper | sort | my_reducer > output

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