src/main/java/org/apache/giraph/graph/partition/RangeWorkerPartitioner.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.giraph.graph.partition;

import java.util.Collection;
import java.util.NavigableMap;
import java.util.TreeMap;

import org.apache.hadoop.io.Writable;
import org.apache.hadoop.io.WritableComparable;

/**
 * Range partitioning will split the vertices by a key range based on a generic
 * type.  This allows vertices that have some locality with the vertex ids
 * to reduce the amount of messages sent.  The tradeoffs are that
 * range partitioning is more susceptible to hot spots if the keys
 * are not randomly distributed.  Another negative is the user must implement
 * some of the functionality around how to split the key range.
 *
 * Note:  This implementation is incomplete, the developer must implement the
 * various methods based on their index type.
 *
 * @param <I> Vertex index value
 * @param <V> Vertex value
 * @param <E> Edge value
 * @param <M> Message value
 */
@SuppressWarnings("rawtypes")
public abstract class RangeWorkerPartitioner<I extends WritableComparable,
        V extends Writable, E extends Writable, M extends Writable> implements
        WorkerGraphPartitioner<I, V, E, M> {
    /** Mapping of the vertex ids to the {@link PartitionOwner} */
    protected NavigableMap<I, RangePartitionOwner<I>> vertexRangeMap =
        new TreeMap<I, RangePartitionOwner<I>>();

    @Override
    public PartitionOwner createPartitionOwner() {
        return new RangePartitionOwner<I>();
    }

    @Override
    public PartitionOwner getPartitionOwner(I vertexId) {
        // Find the partition owner based on the maximum partition id.
        // If the vertex id exceeds any of the maximum partition ids, give
        // it to the last one
        if (vertexId == null) {
            throw new IllegalArgumentException(
                "getPartitionOwner: Illegal null vertex id");
        }
        I maxVertexIndex = vertexRangeMap.ceilingKey(vertexId);
        if (maxVertexIndex == null) {
            return vertexRangeMap.lastEntry().getValue();
        } else {
            return vertexRangeMap.get(vertexId);
        }
    }

    @Override
    public Collection<? extends PartitionOwner> getPartitionOwners() {
        return vertexRangeMap.values();
    }
}