ReachTopology.java

package storm.starter;

import backtype.storm.Config;
import backtype.storm.LocalCluster;
import backtype.storm.LocalDRPC;
import backtype.storm.StormSubmitter;
import backtype.storm.coordination.BatchOutputCollector;
import backtype.storm.drpc.LinearDRPCTopologyBuilder;
import backtype.storm.task.TopologyContext;
import backtype.storm.topology.BasicOutputCollector;
import backtype.storm.topology.OutputFieldsDeclarer;
import backtype.storm.topology.base.BaseBasicBolt;
import backtype.storm.topology.base.BaseBatchBolt;
import backtype.storm.tuple.Fields;
import backtype.storm.tuple.Tuple;
import backtype.storm.tuple.Values;

import java.util.*;

/**
 * This is a good example of doing complex Distributed RPC on top of Storm. This program creates a topology that can
 * compute the reach for any URL on Twitter in realtime by parallelizing the whole computation.
 * <p/>
 * Reach is the number of unique people exposed to a URL on Twitter. To compute reach, you have to get all the people
 * who tweeted the URL, get all the followers of all those people, unique that set of followers, and then count the
 * unique set. It's an intense computation that can involve thousands of database calls and tens of millions of follower
 * records.
 * <p/>
 * This Storm topology does every piece of that computation in parallel, turning what would be a computation that takes
 * minutes on a single machine into one that takes just a couple seconds.
 * <p/>
 * For the purposes of demonstration, this topology replaces the use of actual DBs with in-memory hashmaps.
 * <p/>
 * See https://github.com/nathanmarz/storm/wiki/Distributed-RPC for more information on Distributed RPC.
 */
public class ReachTopology {
  public static Map<String, List<String>> TWEETERS_DB = new HashMap<String, List<String>>() {{
    put("foo.com/blog/1", Arrays.asList("sally", "bob", "tim", "george", "nathan"));
    put("engineering.twitter.com/blog/5", Arrays.asList("adam", "david", "sally", "nathan"));
    put("tech.backtype.com/blog/123", Arrays.asList("tim", "mike", "john"));
  }};

  public static Map<String, List<String>> FOLLOWERS_DB = new HashMap<String, List<String>>() {{
    put("sally", Arrays.asList("bob", "tim", "alice", "adam", "jim", "chris", "jai"));
    put("bob", Arrays.asList("sally", "nathan", "jim", "mary", "david", "vivian"));
    put("tim", Arrays.asList("alex"));
    put("nathan", Arrays.asList("sally", "bob", "adam", "harry", "chris", "vivian", "emily", "jordan"));
    put("adam", Arrays.asList("david", "carissa"));
    put("mike", Arrays.asList("john", "bob"));
    put("john", Arrays.asList("alice", "nathan", "jim", "mike", "bob"));
  }};

  public static class GetTweeters extends BaseBasicBolt {
    @Override
    public void execute(Tuple tuple, BasicOutputCollector collector) {
      Object id = tuple.getValue(0);
      String url = tuple.getString(1);
      List<String> tweeters = TWEETERS_DB.get(url);
      if (tweeters != null) {
        for (String tweeter : tweeters) {
          collector.emit(new Values(id, tweeter));
        }
      }
    }

    @Override
    public void declareOutputFields(OutputFieldsDeclarer declarer) {
      declarer.declare(new Fields("id", "tweeter"));
    }
  }

  public static class GetFollowers extends BaseBasicBolt {
    @Override
    public void execute(Tuple tuple, BasicOutputCollector collector) {
      Object id = tuple.getValue(0);
      String tweeter = tuple.getString(1);
      List<String> followers = FOLLOWERS_DB.get(tweeter);
      if (followers != null) {
        for (String follower : followers) {
          collector.emit(new Values(id, follower));
        }
      }
    }

    @Override
    public void declareOutputFields(OutputFieldsDeclarer declarer) {
      declarer.declare(new Fields("id", "follower"));
    }
  }

  public static class PartialUniquer extends BaseBatchBolt {
    BatchOutputCollector _collector;
    Object _id;
    Set<String> _followers = new HashSet<String>();

    @Override
    public void prepare(Map conf, TopologyContext context, BatchOutputCollector collector, Object id) {
      _collector = collector;
      _id = id;
    }

    @Override
    public void execute(Tuple tuple) {
      _followers.add(tuple.getString(1));
    }

    @Override
    public void finishBatch() {
      _collector.emit(new Values(_id, _followers.size()));
    }

    @Override
    public void declareOutputFields(OutputFieldsDeclarer declarer) {
      declarer.declare(new Fields("id", "partial-count"));
    }
  }

  public static class CountAggregator extends BaseBatchBolt {
    BatchOutputCollector _collector;
    Object _id;
    int _count = 0;

    @Override
    public void prepare(Map conf, TopologyContext context, BatchOutputCollector collector, Object id) {
      _collector = collector;
      _id = id;
    }

    @Override
    public void execute(Tuple tuple) {
      _count += tuple.getInteger(1);
    }

    @Override
    public void finishBatch() {
      _collector.emit(new Values(_id, _count));
    }

    @Override
    public void declareOutputFields(OutputFieldsDeclarer declarer) {
      declarer.declare(new Fields("id", "reach"));
    }
  }

  public static LinearDRPCTopologyBuilder construct() {
    LinearDRPCTopologyBuilder builder = new LinearDRPCTopologyBuilder("reach");
    builder.addBolt(new GetTweeters(), 4);
    builder.addBolt(new GetFollowers(), 12).shuffleGrouping();
    builder.addBolt(new PartialUniquer(), 6).fieldsGrouping(new Fields("id", "follower"));
    builder.addBolt(new CountAggregator(), 3).fieldsGrouping(new Fields("id"));
    return builder;
  }

  public static void main(String[] args) throws Exception {
    LinearDRPCTopologyBuilder builder = construct();


    Config conf = new Config();

    if (args == null || args.length == 0) {
      conf.setMaxTaskParallelism(3);
      LocalDRPC drpc = new LocalDRPC();
      LocalCluster cluster = new LocalCluster();
      cluster.submitTopology("reach-drpc", conf, builder.createLocalTopology(drpc));

      String[] urlsToTry = new String[]{ "foo.com/blog/1", "engineering.twitter.com/blog/5", "notaurl.com" };
      for (String url : urlsToTry) {
        System.out.println("Reach of " + url + ": " + drpc.execute("reach", url));
      }

      cluster.shutdown();
      drpc.shutdown();
    }
    else {
      conf.setNumWorkers(6);
      StormSubmitter.submitTopology(args[0], conf, builder.createRemoteTopology());
    }
  }
}