Friday, 1 May 2015

Data Types in Hadoop

In Hadoop, the two basic data types are:

    WritableComparable is the base interface for keys, and
    Writable is the base class interface for values.

Classes implementing the above two interfaces provide your basic primitives:

byte ----------------- ByteWritable

int ----------------- IntWritable

long ----------------- LongWritable

float ----------------- FloatWritable

boolean ----------------- BooleanWritable

 You can use the following built-in data types as key and value.

    Text :This class stores text using standard UTF8 encoding.
    ByteWritable : This stores a sequence of bytes.
    VIntWritable and VLongWritable : WritableComparable for integer and long values stored in variable-length format.
    Nullwritable:This is zero-length Writable type that can be used when you don’t want to use a key or value type.

The following hadoop built-in collection data types can only be used as value types


 ArrayWritable:This stores an array of values belonging to a Writable type.
 TwoDArrayWritable:This stores a matrix of values belonging to the same Writable type.


 MapWritable:This stores a map of key-value pairs.keys and values should be of the writable  datatypes (Map<Writable,Writable>).
SortedMapwritable:This stores a sorte map of key-value pairs.Keys should implement the WritableComparable interface ( SortedMap<WritableComparable,Writable> ).

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