/*
* 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.solr.hadoop;
import java.io.IOException;
import java.lang.invoke.MethodHandles;
import java.util.Random;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* MR Mapper that randomizing a list of URLs.
*
* Mapper input is (offset, URL) pairs. Each such pair indicates a file to
* index.
*
* Mapper output is (randomPosition, URL) pairs. The reducer receives these
* pairs sorted by randomPosition.
*/
public class LineRandomizerMapper extends Mapper<LongWritable, Text, LongWritable, Text> {
private Random random;
private static final Logger LOGGER = LoggerFactory.getLogger(MethodHandles.lookup().lookupClass());
@Override
protected void setup(Context context) throws IOException, InterruptedException {
super.setup(context);
random = createRandom(context);
}
@Override
protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
LOGGER.debug("map key: {}, value: {}", key, value);
context.write(new LongWritable(random.nextLong()), value);
}
private Random createRandom(Context context) {
long taskId = 0;
if (context.getTaskAttemptID() != null) { // MRUnit returns null
LOGGER.debug("context.getTaskAttemptID().getId(): {}", context.getTaskAttemptID().getId());
LOGGER.debug("context.getTaskAttemptID().getTaskID().getId(): {}", context.getTaskAttemptID().getTaskID().getId());
taskId = context.getTaskAttemptID().getTaskID().getId(); // taskId = 0, 1, ..., N
}
// create a good random seed, yet ensure deterministic PRNG sequence for easy reproducability
return new Random(421439783L * (taskId + 1));
}
}