Use Oozie to run terasort

The better choice of “Action” for running terasort test case in Oozie is “Java Action” instead of “Mapreduce Action” because terasort need to run

first and then load ‘partitonFile’ by “TotalOrderPartitioner”. It’s not a simple Mapreduce job which need merely a few propertyies.

The directory of this”TerasortApp” which using “Java Action” of Oozie looks just like:

The core of this App is “workflow.xml”:

Note 1. In Cloudera environment, The Web UI will fail in the last step of creating sharelib for Oozie Service. To fix this problem:

Note 2. We can’t use property of ‘’ to change the number of mappers in Terasort because it is actually decided by class ‘TotalOrderPartitioner’. Therefore I use ‘mapreduce.input.fileinputformat.split.minsize’ property to limit the number of mappers.

Some problems about programming Mapreduce

1. After submitting job, the console report:

The reason is I forgot to setJarByClass():

2. When the job finished, I found the reducer haven’t run at all. The reason is I haven’t override the correct reduce() member function of Reducer so MapReduce Framework ignore it and didn’t report any notification or warning. To make sure we override the correct member function of parent class, we need to add annotation:

Use MapReduce to join two datasets

The two datasets are:

To join the two tables above by “student id”, we need to use MultipleInputs. The code is:

Compile and run it:

And the result in /my is:

Use MapReduce to find prime numbers

Just want to write a small example of MapReduce of Hadoop for finding prime numbers. The first question is: how could I generate numbers from 1 to 1000000 by my own application instead of reading from file of HDFS? The answer is: inherit the InputSplit, RecordReader, and InputFormat by yourself, just like teragen program
Then comes the second question: could I just use mapper without reducer stage? The answer is yes, simply use job.setNumReduceTasks(0) to disable reducer stage.

The complete code is here (I know the algorithm for checking a number for prime is naive, but it works):

Copy the code to file, compile and run it: