/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.pig.backend.hadoop.executionengine.mapReduceLayer;
import java.io.IOException;
import java.util.Iterator;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.io.Writable;
import org.apache.hadoop.mapred.JobConf;
import org.apache.hadoop.mapred.MapReduceBase;
import org.apache.hadoop.mapred.OutputCollector;
import org.apache.hadoop.mapred.Reducer;
import org.apache.hadoop.mapred.Reporter;
import org.apache.pig.impl.io.PigNullableWritable;
import org.apache.pig.impl.io.NullableTuple;
/**
* A special implementation of combiner used only for distinct. This combiner
* does not even parse out the records. It just throws away duplicate values
* in the key in order ot minimize the data being sent to the reduce.
*/
public class DistinctCombiner {
public static class Combine extends MapReduceBase
implements
Reducer<PigNullableWritable, NullableTuple, PigNullableWritable, Writable> {
private final Log log = LogFactory.getLog(getClass());
ProgressableReporter pigReporter;
/**
* Configures the reporter
*/
@Override
public void configure(JobConf jConf) {
super.configure(jConf);
pigReporter = new ProgressableReporter();
}
/**
* The reduce function which removes values.
*/
public void reduce(PigNullableWritable key,
Iterator<NullableTuple> tupIter,
OutputCollector<PigNullableWritable, Writable> oc,
Reporter reporter) throws IOException {
pigReporter.setRep(reporter);
// Take the first value and the key and collect
// just that.
NullableTuple val = tupIter.next();
oc.collect(key, val);
}
}
}