src/org/apache/pig/impl/io/InterRecordWriter.java

/*
 * 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.impl.io;

import java.io.IOException;
import java.rmi.server.UID;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

import org.apache.hadoop.fs.FSDataOutputStream;
import org.apache.hadoop.io.WritableComparable;
import org.apache.hadoop.mapreduce.RecordWriter;
import org.apache.hadoop.mapreduce.TaskAttemptContext;
import org.apache.hadoop.util.Time;
import org.apache.pig.data.InterSedes;
import org.apache.pig.data.InterSedesFactory;
import org.apache.pig.data.Tuple;


/**
 * A record reader used to write data compatible with {@link InterRecordWriter}
 * It uses the default InterSedes object for serialization.
 */
public class InterRecordWriter extends
        RecordWriter<org.apache.hadoop.io.WritableComparable, Tuple> {

    private static InterSedes sedes = InterSedesFactory.getInterSedesInstance();

    private byte[] syncMarker;
    private long lastSyncPos = -1;
    private long syncMarkerInterval;
    /**
     * the outputstream to write out on
     */
    private FSDataOutputStream out;
    
    /**
     * 
     */
    public InterRecordWriter(FSDataOutputStream out, int syncMarkerLength, long syncMarkerInterval) {
        this.out = out;
        this.syncMarkerInterval = syncMarkerInterval;
        syncMarker = new byte[syncMarkerLength];

        try {
            MessageDigest digester = MessageDigest.getInstance("MD5");
            long time = Time.now();
            digester.update((new UID()+"@"+time).getBytes());
            byte[] generatedMarker = digester.digest();
            System.arraycopy(generatedMarker, 0, syncMarker, 0, syncMarkerLength);
        } catch (NoSuchAlgorithmException e) {
            throw new RuntimeException(e);
        }

    }

    /* (non-Javadoc)
     * @see org.apache.hadoop.mapreduce.RecordWriter#close(org.apache.hadoop.mapreduce.TaskAttemptContext)
     */
    @Override
    public void close(TaskAttemptContext arg0) throws IOException,
            InterruptedException {
        out.close();        
    }

    /* (non-Javadoc)
     * @see org.apache.hadoop.mapreduce.RecordWriter#write(java.lang.Object, java.lang.Object)
     */
    @Override
    public void write(WritableComparable wc, Tuple t) throws IOException,
            InterruptedException {
        // we really only want to write the tuple (value) out here (and a sync syncMarker before that if necessary)
        if (lastSyncPos == -1 || out.getPos() >= (lastSyncPos + syncMarkerInterval)) {
            out.write(syncMarker);
            lastSyncPos = out.getPos();
        }
        sedes.writeDatum(out, t);
        
    }

}