001 /**
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements. See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership. The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License. You may obtain a copy of the License at
009 *
010 * http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018
019 package org.apache.hadoop.mapreduce.lib.join;
020
021 import java.io.IOException;
022 import java.util.ArrayList;
023 import java.util.PriorityQueue;
024
025 import org.apache.hadoop.classification.InterfaceAudience;
026 import org.apache.hadoop.classification.InterfaceStability;
027 import org.apache.hadoop.conf.Configuration;
028 import org.apache.hadoop.io.NullWritable;
029 import org.apache.hadoop.io.Writable;
030 import org.apache.hadoop.io.WritableComparable;
031 import org.apache.hadoop.io.WritableComparator;
032 import org.apache.hadoop.util.ReflectionUtils;
033
034 /**
035 * Prefer the "rightmost" data source for this key.
036 * For example, <tt>override(S1,S2,S3)</tt> will prefer values
037 * from S3 over S2, and values from S2 over S1 for all keys
038 * emitted from all sources.
039 */
040 @InterfaceAudience.Public
041 @InterfaceStability.Stable
042 public class OverrideRecordReader<K extends WritableComparable<?>,
043 V extends Writable>
044 extends MultiFilterRecordReader<K,V> {
045
046 OverrideRecordReader(int id, Configuration conf, int capacity,
047 Class<? extends WritableComparator> cmpcl) throws IOException {
048 super(id, conf, capacity, cmpcl);
049 }
050 private Class<? extends Writable> valueclass = null;
051
052 /**
053 * Emit the value with the highest position in the tuple.
054 */
055 @SuppressWarnings("unchecked") // No static typeinfo on Tuples
056 protected V emit(TupleWritable dst) {
057 return (V) dst.iterator().next();
058 }
059
060 @SuppressWarnings("unchecked") // Explicit check for value class agreement
061 public V createValue() {
062 if (null == valueclass) {
063 Class<?> cls = kids[kids.length -1].createValue().getClass();
064 for (int i = kids.length -1; cls.equals(NullWritable.class); i--) {
065 cls = kids[i].createValue().getClass();
066 }
067 valueclass = cls.asSubclass(Writable.class);
068 }
069 if (valueclass.equals(NullWritable.class)) {
070 return (V) NullWritable.get();
071 }
072 return (V) ReflectionUtils.newInstance(valueclass, null);
073 }
074
075 /**
076 * Instead of filling the JoinCollector with iterators from all
077 * data sources, fill only the rightmost for this key.
078 * This not only saves space by discarding the other sources, but
079 * it also emits the number of key-value pairs in the preferred
080 * RecordReader instead of repeating that stream n times, where
081 * n is the cardinality of the cross product of the discarded
082 * streams for the given key.
083 */
084 protected void fillJoinCollector(K iterkey)
085 throws IOException, InterruptedException {
086 final PriorityQueue<ComposableRecordReader<K,?>> q =
087 getRecordReaderQueue();
088 if (q != null && !q.isEmpty()) {
089 int highpos = -1;
090 ArrayList<ComposableRecordReader<K,?>> list =
091 new ArrayList<ComposableRecordReader<K,?>>(kids.length);
092 q.peek().key(iterkey);
093 final WritableComparator cmp = getComparator();
094 while (0 == cmp.compare(q.peek().key(), iterkey)) {
095 ComposableRecordReader<K,?> t = q.poll();
096 if (-1 == highpos || list.get(highpos).id() < t.id()) {
097 highpos = list.size();
098 }
099 list.add(t);
100 if (q.isEmpty())
101 break;
102 }
103 ComposableRecordReader<K,?> t = list.remove(highpos);
104 t.accept(jc, iterkey);
105 for (ComposableRecordReader<K,?> rr : list) {
106 rr.skip(iterkey);
107 }
108 list.add(t);
109 for (ComposableRecordReader<K,?> rr : list) {
110 if (rr.hasNext()) {
111 q.add(rr);
112 }
113 }
114 }
115 }
116
117 }