/**
* 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.join;
import java.io.IOException;
import java.util.ArrayList;
import java.util.PriorityQueue;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.io.Writable;
import org.apache.hadoop.io.WritableComparable;
import org.apache.hadoop.io.WritableComparator;
import org.apache.hadoop.mapred.JobConf;
/**
* Prefer the "rightmost" data source for this key.
* For example, <tt>override(S1,S2,S3)</tt> will prefer values
* from S3 over S2, and values from S2 over S1 for all keys
* emitted from all sources.
*/
@InterfaceAudience.Public
@InterfaceStability.Stable
public class OverrideRecordReader<K extends WritableComparable,
V extends Writable>
extends MultiFilterRecordReader<K,V> {
OverrideRecordReader(int id, JobConf conf, int capacity,
Class<? extends WritableComparator> cmpcl) throws IOException {
super(id, conf, capacity, cmpcl);
}
/**
* Emit the value with the highest position in the tuple.
*/
@SuppressWarnings("unchecked") // No static typeinfo on Tuples
protected V emit(TupleWritable dst) {
return (V) dst.iterator().next();
}
/**
* Instead of filling the JoinCollector with iterators from all
* data sources, fill only the rightmost for this key.
* This not only saves space by discarding the other sources, but
* it also emits the number of key-value pairs in the preferred
* RecordReader instead of repeating that stream n times, where
* n is the cardinality of the cross product of the discarded
* streams for the given key.
*/
protected void fillJoinCollector(K iterkey) throws IOException {
final PriorityQueue<ComposableRecordReader<K,?>> q = getRecordReaderQueue();
if (!q.isEmpty()) {
int highpos = -1;
ArrayList<ComposableRecordReader<K,?>> list =
new ArrayList<ComposableRecordReader<K,?>>(kids.length);
q.peek().key(iterkey);
final WritableComparator cmp = getComparator();
while (0 == cmp.compare(q.peek().key(), iterkey)) {
ComposableRecordReader<K,?> t = q.poll();
if (-1 == highpos || list.get(highpos).id() < t.id()) {
highpos = list.size();
}
list.add(t);
if (q.isEmpty())
break;
}
ComposableRecordReader<K,?> t = list.remove(highpos);
t.accept(jc, iterkey);
for (ComposableRecordReader<K,?> rr : list) {
rr.skip(iterkey);
}
list.add(t);
for (ComposableRecordReader<K,?> rr : list) {
if (rr.hasNext()) {
q.add(rr);
}
}
}
}
}