Question

What is a SequenceFile?

A. A SequenceFile contains a binary encoding of an arbitrary number of homogeneous Writable objects
B. A SequenceFile contains a binary encoding of an arbitrary number of heterogeneous Writable objects
C. A SequenceFile contains a binary encoding of an arbitrary number of WritableComparable objects, in sorted order.
D. A SequenceFile contains a binary encoding of an arbitrary number key-value pairs. Each key must
be the same type. Each value must be the same type.

Answer 1

Answer: D

Explanation:
SequenceFile is a flat file consisting of binary key/value pairs.

There are 3 different SequenceFile formats:

- Uncompressed key/value records.
- Record compressed key/value records - only 'values' are compressed here.
- Block compressed key/value records - both keys and values are collected in 'blocks' separately and compressed. The size of the 'block' is configurable.

Reference:
http://wiki.apache.org/hadoop/SequenceFile