Hadoop 面试题与答案

问题 11. What is TextInputFormat in Hadoop?

In TextInputFormat, each line in the text file is a record. Value is the content of the line while Key is the byte offset of the line. For instance, Key: longWritable, Value: text

问题 12. What is the SequenceFileInputFormat in Hadoop?

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.

问题 13. How many InputSplits is made by a Hadoop Framework?

Hadoop makes 5 splits as follows:

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

问题 14. What is the use of RecordReader in Hadoop?

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.

问题 15. What is JobTracker in Hadoop?

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