org.apache.hama.bsp.join.OverrideRecordReader.java Source code

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Here is the source code for org.apache.hama.bsp.join.OverrideRecordReader.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.hama.bsp.join;

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

import org.apache.hadoop.io.Writable;
import org.apache.hadoop.io.WritableComparable;
import org.apache.hadoop.io.WritableComparator;
import org.apache.hama.bsp.BSPJob;

/**
 * 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.
 */
public class OverrideRecordReader<K extends WritableComparable, V extends Writable>
        extends MultiFilterRecordReader<K, V> {

    OverrideRecordReader(int id, BSPJob job, int capacity, Class<? extends WritableComparator> cmpcl)
            throws IOException {
        super(id, job, 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);
                }
            }
        }
    }

}