How-To: Run a MapReduce Job in CDH4 by Sandy Ryza.
From the post:
This is the first post in series that will get you going on how to write, compile, and run a simple MapReduce job on Apache Hadoop. The full code, along with tests, is available at http://github.com/cloudera/mapreduce-tutorial. The program will run on either MR1 or MR2.
We’ll assume that you have a running Hadoop installation, either locally or on a cluster, and your environment is set up correctly so that typing “hadoop” into your command line gives you some notes on usage. Detailed instructions for installing CDH, Cloudera’s open-source, enterprise-ready distro of Hadoop and related projects, are available here: https://ccp.cloudera.com/display/CDH4DOC/CDH4+Installation. We’ll also assume you have Maven installed on your system, as this will make compiling your code easier. Note that Maven is not a strict dependency; we could also compile using Java on the command line or with an IDE like Eclipse.
The Use Case
There’s been a lot of brawling on our pirate ship recently. Not so rarely, one of the mates will punch another one in the mouth, knocking a tooth out onto the deck. Our poor sailors will wake up the next day with an empty bottle of rum, wondering who’s responsible for the gap between their teeth. All this violence has gotten out of hand, so as a deterrent, we’d like to provide everyone with a list of everyone that’s ever left them with a gap. Luckily, we’ve been able to set up a Flume source so that every time someone punches someone else, it gets written out as a line in a big log file in Hadoop. To turn this data into these lists, we need a MapReduce job that can 1) invert the mapping from attacker to their victim, 2) group by victims, and 3) eliminate duplicates.
Cool!
Imagine using the same technique while you watch the evening news!
On second thought, that would take too much data entry and be depressing.
Stick to the pirates!