/// <summary>Sets the Reducer class to the chain job's JobConf.</summary>
/// <remarks>
/// Sets the Reducer class to the chain job's JobConf.
/// <p>
/// It has to be specified how key and values are passed from one element of
/// the chain to the next, by value or by reference. If a Reducer leverages the
/// assumed semantics that the key and values are not modified by the collector
/// 'by value' must be used. If the Reducer does not expect this semantics, as
/// an optimization to avoid serialization and deserialization 'by reference'
/// can be used.
/// <p>
/// For the added Reducer the configuration given for it,
/// <code>reducerConf</code>, have precedence over the job's JobConf. This
/// precedence is in effect when the task is running.
/// <p>
/// IMPORTANT: There is no need to specify the output key/value classes for the
/// ChainReducer, this is done by the setReducer or the addMapper for the last
/// element in the chain.
/// </remarks>
/// <param name="job">job's JobConf to add the Reducer class.</param>
/// <param name="klass">the Reducer class to add.</param>
/// <param name="inputKeyClass">reducer input key class.</param>
/// <param name="inputValueClass">reducer input value class.</param>
/// <param name="outputKeyClass">reducer output key class.</param>
/// <param name="outputValueClass">reducer output value class.</param>
/// <param name="byValue">
/// indicates if key/values should be passed by value
/// to the next Mapper in the chain, if any.
/// </param>
/// <param name="reducerConf">
/// a JobConf with the configuration for the Reducer
/// class. It is recommended to use a JobConf without default values using the
/// <code>JobConf(boolean loadDefaults)</code> constructor with FALSE.
/// </param>
public static void SetReducer <K1, V1, K2, V2>(JobConf job, Type klass, Type inputKeyClass
, Type inputValueClass, Type outputKeyClass, Type outputValueClass, bool byValue
, JobConf reducerConf)
{
job.SetReducerClass(typeof(Org.Apache.Hadoop.Mapred.Lib.ChainReducer));
job.SetOutputKeyClass(outputKeyClass);
job.SetOutputValueClass(outputValueClass);
Chain.SetReducer(job, klass, inputKeyClass, inputValueClass, outputKeyClass, outputValueClass
, byValue, reducerConf);
}
public virtual void TestSetReducerWithReducerByValueAsFalse()
{
JobConf jobConf = new JobConf();
JobConf reducerConf = new JobConf();
Chain.SetReducer(jobConf, typeof(TestChain.MyReducer), typeof(object), typeof(object
), typeof(object), typeof(object), false, reducerConf);
bool reduceByValue = reducerConf.GetBoolean("chain.reducer.byValue", true);
NUnit.Framework.Assert.AreEqual("It should set chain.reducer.byValue as false " +
"in reducerConf when we give value as false", false, reduceByValue);
}