环境配置

Hadoop配置

这里使用Hadoop2.5.1进行配置，可以参考这里。

查看版本号

运行Hadoop

./hadoop-2.5.1/sbin/start-dfs.sh

查看是否成功

Giraph配置

下载Giraph

cd /usr/local
sudo git clone https://github.com/apache/giraph.git
sudo chown -R hadoop:hadoop giraph

编译

cd giraph
mvn -Phadoop_2 -Dhadoop.version=2.5.1 -DskipTests clean package

编译成功：

运行

执行最短路径程序

输入

创建/tmp/tiny_graph.txt，输入:

[0,0,[[1,1],[3,3]]]
[1,0,[[0,1],[2,2],[3,1]]]
[2,0,[[1,2],[4,4]]]
[3,0,[[0,3],[1,1],[4,4]]]
[4,0,[[3,4],[2,4]]]

每一条线由[source_id,source_value,[[dest_id, edge_value],...]]构成。

并拷贝到HDFS中：

cd /usr/local
hadoop-2.5.1/bin/hadoop dfs -copyFromLocal /tmp/tiny_graph.txt /tiny_graph.txt

提交任务

/usr/local/hadoop-2.5.1/bin/hadoop jar /usr/local/giraph/giraph-examples/target/giraph-examples-1.3.0-SNAPSHOT-for-hadoop-2.5.1-jar-with-dependencies.jar org.apache.giraph.GiraphRunner org.apache.giraph.examples.SimpleShortestPathsComputation -vif org.apache.giraph.io.formats.JsonLongDoubleFloatDoubleVertexInputFormat -vip /tiny_graph.txt -vof org.apache.giraph.io.formats.IdWithValueTextOutputFormat -op /shortestpaths -w 1 -ca giraph.SplitMasterWorker=false

查看结果

每个点离点1的最短路径：

查看代码例子

package org.apache.giraph.examples;

import org.apache.giraph.graph.BasicComputation;
import org.apache.giraph.conf.LongConfOption;
import org.apache.giraph.edge.Edge;
import org.apache.giraph.graph.Vertex;
import org.apache.hadoop.io.DoubleWritable;
import org.apache.hadoop.io.FloatWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.log4j.Logger;

import java.io.IOException;

/**
 * Demonstrates the basic Pregel shortest paths implementation.
 */
@Algorithm(
    name = "Shortest paths",
    description = "Finds all shortest paths from a selected vertex"
)
public class SimpleShortestPathsComputation extends BasicComputation<
    LongWritable, DoubleWritable, FloatWritable, DoubleWritable> {
  /** The shortest paths id */
  public static final LongConfOption SOURCE_ID =
      new LongConfOption("SimpleShortestPathsVertex.sourceId", 1,
          "The shortest paths id");
  /** Class logger */
  private static final Logger LOG =
      Logger.getLogger(SimpleShortestPathsComputation.class);

  /**
   * Is this vertex the source id?
   *
   * @param vertex Vertex
   * @return True if the source id
   */
  private boolean isSource(Vertex<LongWritable, ?, ?> vertex) {
    return vertex.getId().get() == SOURCE_ID.get(getConf());
  }

  @Override
  public void compute(
      Vertex<LongWritable, DoubleWritable, FloatWritable> vertex,
      Iterable<DoubleWritable> messages) throws IOException {
    if (getSuperstep() == 0) {
      vertex.setValue(new DoubleWritable(Double.MAX_VALUE));
    }
    double minDist = isSource(vertex) ? 0d : Double.MAX_VALUE;
    for (DoubleWritable message : messages) {
      minDist = Math.min(minDist, message.get());
    }
    if (LOG.isDebugEnabled()) {
      LOG.debug("Vertex " + vertex.getId() + " got minDist = " + minDist +
          " vertex value = " + vertex.getValue());
    }
    if (minDist < vertex.getValue().get()) {
      vertex.setValue(new DoubleWritable(minDist));
      for (Edge<LongWritable, FloatWritable> edge : vertex.getEdges()) {
        double distance = minDist + edge.getValue().get();
        if (LOG.isDebugEnabled()) {
          LOG.debug("Vertex " + vertex.getId() + " sent to " +
              edge.getTargetVertexId() + " = " + distance);
        }
        sendMessage(edge.getTargetVertexId(), new DoubleWritable(distance));
      }
    }
    vertex.voteToHalt();
  }
}

主要就两个函数：

1. compute
   • 执行实际的计算
2. sendMessage
   • 发送消息