org.apache.hadoop.mapred.MultiFileInputFormat.java Source code

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Here is the source code for org.apache.hadoop.mapred.MultiFileInputFormat.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.mapred;

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

import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.FileUtil;
import org.apache.hadoop.fs.Path;

/**
 * An abstract {@link InputFormat} that returns {@link MultiFileSplit}'s
 * in {@link #getSplits(JobConf, int)} method. Splits are constructed from 
 * the files under the input paths. Each split returned contains <i>nearly</i>
 * equal content length. <br>  
 * Subclasses implement {@link #getRecordReader(InputSplit, JobConf, Reporter)}
 * to construct <code>RecordReader</code>'s for <code>MultiFileSplit</code>'s.
 * @see MultiFileSplit
 */
@InterfaceAudience.Public
@InterfaceStability.Stable
public abstract class MultiFileInputFormat<K, V> extends FileInputFormat<K, V> {

    @Override
    public InputSplit[] getSplits(JobConf job, int numSplits) throws IOException {

        Path[] paths = FileUtil.stat2Paths(listStatus(job));
        List<MultiFileSplit> splits = new ArrayList<MultiFileSplit>(Math.min(numSplits, paths.length));
        if (paths.length != 0) {
            // HADOOP-1818: Manage splits only if there are paths
            long[] lengths = new long[paths.length];
            long totLength = 0;
            for (int i = 0; i < paths.length; i++) {
                FileSystem fs = paths[i].getFileSystem(job);
                lengths[i] = fs.getContentSummary(paths[i]).getLength();
                totLength += lengths[i];
            }
            double avgLengthPerSplit = ((double) totLength) / numSplits;
            long cumulativeLength = 0;

            int startIndex = 0;

            for (int i = 0; i < numSplits; i++) {
                int splitSize = findSize(i, avgLengthPerSplit, cumulativeLength, startIndex, lengths);
                if (splitSize != 0) {
                    // HADOOP-1818: Manage split only if split size is not equals to 0
                    Path[] splitPaths = new Path[splitSize];
                    long[] splitLengths = new long[splitSize];
                    System.arraycopy(paths, startIndex, splitPaths, 0, splitSize);
                    System.arraycopy(lengths, startIndex, splitLengths, 0, splitSize);
                    splits.add(new MultiFileSplit(job, splitPaths, splitLengths));
                    startIndex += splitSize;
                    for (long l : splitLengths) {
                        cumulativeLength += l;
                    }
                }
            }
        }
        return splits.toArray(new MultiFileSplit[splits.size()]);
    }

    private int findSize(int splitIndex, double avgLengthPerSplit, long cumulativeLength, int startIndex,
            long[] lengths) {

        if (splitIndex == lengths.length - 1)
            return lengths.length - startIndex;

        long goalLength = (long) ((splitIndex + 1) * avgLengthPerSplit);
        long partialLength = 0;
        // accumulate till just above the goal length;
        for (int i = startIndex; i < lengths.length; i++) {
            partialLength += lengths[i];
            if (partialLength + cumulativeLength >= goalLength) {
                return i - startIndex + 1;
            }
        }
        return lengths.length - startIndex;
    }

    @Override
    public abstract RecordReader<K, V> getRecordReader(InputSplit split, JobConf job, Reporter reporter)
            throws IOException;
}