• InputFormat
• SequenceFileInputFormat
• SequenceFileInputFormat
• TextInputFormat
• ObjectPositionInputFormat
• FileInputFormat
• ToolRunner
• LocalJobRunner
• job.setNumReduceTasks(8);job.setPartitionerClass(MyPartitioner.class);
• Write a custom FileInputFormat and override the method isSplitable to always return false
• MRUnit 
• hadoop fs -setrep 4 f1
• hadoop fs -Ddfs.replication=4 -cp f1 f1.tmp; hadoop fs -rm f1; hadoop fs -mv f1.tmp f1
• How are keys and values presented and passed to the reduce() method during a standard shuffle and sort phase of MapReduce?
• Does the MapReduce programming model provide a way for reduce tasks to communicate with each other?
• Speculative Execution
• WritableComparable
• Workflow of Oozie
• A single map task processes <>?
• Hive table field delimiters
• When testing a Reducer using MRUnit, you should only pass the Reducer a single key and list of values. In this case, we use the withInput() method twice, but only the second call will actually be used -- the first will be overridden by the second. If you want to test the Reducer with two inputs, you would have to write two tests.