com.bigdata.service.mapred
Interface IReduceTask

All Superinterfaces:

ITask, Serializable

All Known Implementing Classes:

AbstractReduceTask, CountKeywords

public interface IReduceTask
extends ITask

Interface for a reduce task to be executed on a map/reduce client.

Version:

$Id: IReduceTask.java 2265 2009-10-26 12:51:06Z thompsonbry $

Author:

Bryan Thompson

Method Summary

UUID	getDataService() The IDataService from which the reduce task will read its input.
void	reduce(byte[] key, Iterator<byte[]> vals) Each reduce task will be presented with a series of key-value pairs in key order.

Methods inherited from interface com.bigdata.service.mapred.ITask

getUUID

Method Detail

getDataService

UUID getDataService()

The IDataService from which the reduce task will read its input.

reduce

void reduce(byte[] key,
            Iterator<byte[]> vals)
            throws Exception

Each reduce task will be presented with a series of key-value pairs in key order. However, the keys will be distributed across the N reduce tasks by the used defined hash function, so this is NOT a total ordering over the intermediate keys.

Note: This method is never invoked for a key for which there are no values.

Parameters:

key - A key.

vals - An iterator that will visit the set of values for that key.

Throws:

Exception