DistinctConverter.java

package org.apache.pig.backend.hadoop.executionengine.spark.converter;

import java.io.IOException;
import java.io.Serializable;
import java.util.List;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.pig.backend.hadoop.executionengine.physicalLayer.relationalOperators.PODistinct;
import org.apache.pig.backend.hadoop.executionengine.spark.ScalaUtil;
import org.apache.pig.backend.hadoop.executionengine.spark.SparkUtil;
import org.apache.pig.data.Tuple;
import org.apache.spark.rdd.PairRDDFunctions;
import org.apache.spark.rdd.RDD;

import scala.Function1;
import scala.Function2;
import scala.Tuple2;
import scala.reflect.ClassTag;
import scala.runtime.AbstractFunction1;
import scala.runtime.AbstractFunction2;

/**
 * PODistinct转RDD操作 <br/>
 * 这里的Distinct操纵相当于RDD.distinct(numPartitions: Int)
 * 
 * @author zhangbaofeng
 * 
 */
public class DistinctConverter implements POConverter<Tuple, Tuple, PODistinct> {
	private static final Log LOG = LogFactory.getLog(DistinctConverter.class);

	private static final Function1<Tuple, Tuple2<Tuple, Object>> TO_KEY_VALUE_FUNCTION = new ToKeyValueFunction();
	private static final Function2<Object, Object, Object> MERGE_VALUES_FUNCTION = new MergeValuesFunction();
	private static final Function1<Tuple2<Tuple, Object>, Tuple> TO_VALUE_FUNCTION = new ToValueFunction();

	@Override
	public RDD<Tuple> convert(List<RDD<Tuple>> predecessors, PODistinct poDistinct) throws IOException {
		SparkUtil.assertPredecessorSize(predecessors, poDistinct, 1);

		RDD<Tuple> rdd = predecessors.get(0);

		ClassTag<Tuple2<Tuple, Object>> tuple2ClassTag = ScalaUtil.<Tuple, Object> getTuple2ClassTag();

		RDD<Tuple2<Tuple, Object>> rddPairs = rdd.map(TO_KEY_VALUE_FUNCTION, tuple2ClassTag);

		PairRDDFunctions<Tuple, Object> pairRDDFunctions = 
			new PairRDDFunctions<Tuple, Object>(rddPairs, ScalaUtil.getClassTag(Tuple.class), ScalaUtil.getClassTag(Object.class));

		int parallelism = SparkUtil.getParallelism(predecessors, poDistinct);

		return pairRDDFunctions.reduceByKey(MERGE_VALUES_FUNCTION, parallelism)
				               .map(TO_VALUE_FUNCTION, ScalaUtil.getClassTag(Tuple.class));
	}

	@SuppressWarnings("serial")
	private static final class ToKeyValueFunction extends AbstractFunction1<Tuple, Tuple2<Tuple, Object>> 
			implements Serializable {
		@Override
		public Tuple2<Tuple, Object> apply(Tuple t) {
			if (LOG.isDebugEnabled()) {
				LOG.debug("DistinctConverter.ToKeyValueFunction in " + t);				
			}
			Tuple key = t;
			Object value = null;
			// (key, value)
			Tuple2<Tuple, Object> out = new Tuple2<Tuple, Object>(key, value);
			if (LOG.isDebugEnabled()) {
				LOG.debug("DistinctConverter.ToKeyValueFunction out " + out);
			}
			return out;
		}
	}

	@SuppressWarnings("serial")
	private static final class MergeValuesFunction extends AbstractFunction2<Object, Object, Object> 
			implements Serializable {
		@Override
		public Object apply(Object arg0, Object arg1) {
			return null;
		}
	}

	@SuppressWarnings("serial")
	private static final class ToValueFunction extends AbstractFunction1<Tuple2<Tuple, Object>, Tuple> 
			implements Serializable {
		@Override
		public Tuple apply(Tuple2<Tuple, Object> input) {
			return input._1;
		}
	}
}