org.apache.hadoop.hive.ql.exec.tez.tools.InputMerger.java Source code

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Here is the source code for org.apache.hadoop.hive.ql.exec.tez.tools.InputMerger.java

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/**
 * 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.hadoop.hive.ql.exec.tez.tools;

import java.io.IOException;
import java.util.Comparator;
import java.util.List;
import java.util.PriorityQueue;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.hive.ql.exec.tez.ReduceRecordProcessor;
import org.apache.hadoop.io.BinaryComparable;
import org.apache.tez.runtime.api.Input;
import org.apache.tez.runtime.api.LogicalInput;
import org.apache.tez.runtime.library.api.KeyValuesReader;

/**
 * A KeyValuesReader implementation that returns a sorted stream of key-values
 * by doing a sorted merge of the key-value in LogicalInputs.
 * Tags are in the last byte of the key, so no special handling for tags is required.
 * Uses a priority queue to pick the KeyValuesReader of the input that is next in
 * sort order.
 */
public class InputMerger implements KeyValuesReader {

    public static final Log l4j = LogFactory.getLog(ReduceRecordProcessor.class);
    private PriorityQueue<KeyValuesReader> pQueue = null;
    private KeyValuesReader nextKVReader = null;

    public InputMerger(List<? extends Input> shuffleInputs) throws Exception {
        //get KeyValuesReaders from the LogicalInput and add them to priority queue
        int initialCapacity = shuffleInputs.size();
        pQueue = new PriorityQueue<KeyValuesReader>(initialCapacity, new KVReaderComparator());
        for (Input input : shuffleInputs) {
            addToQueue((KeyValuesReader) input.getReader());
        }
    }

    /**
     * Add KeyValuesReader to queue if it has more key-values
     * @param kvsReadr
     * @throws IOException
     */
    private void addToQueue(KeyValuesReader kvsReadr) throws IOException {
        if (kvsReadr.next()) {
            pQueue.add(kvsReadr);
        }
    }

    /**
     * @return true if there are more key-values and advances to next key-values
     * @throws IOException
     */
    public boolean next() throws IOException {
        //add the previous nextKVReader back to queue
        if (nextKVReader != null) {
            addToQueue(nextKVReader);
        }

        //get the new nextKVReader with lowest key
        nextKVReader = pQueue.poll();
        return nextKVReader != null;
    }

    public Object getCurrentKey() throws IOException {
        return nextKVReader.getCurrentKey();
    }

    public Iterable<Object> getCurrentValues() throws IOException {
        return nextKVReader.getCurrentValues();
    }

    /**
     * Comparator that compares KeyValuesReader on their current key
     */
    class KVReaderComparator implements Comparator<KeyValuesReader> {

        @Override
        public int compare(KeyValuesReader kvReadr1, KeyValuesReader kvReadr2) {
            try {
                BinaryComparable key1 = (BinaryComparable) kvReadr1.getCurrentKey();
                BinaryComparable key2 = (BinaryComparable) kvReadr2.getCurrentKey();
                return key1.compareTo(key2);
            } catch (IOException e) {
                l4j.error("Caught exception while reading shuffle input", e);
                //die!
                throw new RuntimeException(e);
            }
        }
    }

}