Interview Questions and Answers

In Hadoop, SequenceFileInputFormat is used to read files in sequence. It is a specific compressed binary file format which passes data between the output of one MapReduce job to the input of some other MapReduce job.

Hadoop makes 5 splits as follows:

• One split for 64K files
• Two splits for 65MB files, and
• Two splits for 127MB files

InputSplit is assigned with a work but doesn't know how to access it. The record holder class is totally responsible for loading the data from its source and convert it into keys pair suitable for reading by the Mapper. The RecordReader's instance can be defined by the Input Format.

JobTracker is a service within Hadoop which runs MapReduce jobs on the cluster.

Following are the three configuration files in Hadoop:

• core-site.xml
• mapred-site.xml
• hdfs-site.xml