Hadoop Cascading - create flow with one source, two sinks

Question

I am using Cascading 2 to create Hadoop jobs and am trying to create a flow that starts with a single source. After a couple of functions are applied to the data I need to split the flow so that this data is used to create two separate reports (in two separate sinks).

    //SOURCE
    Scheme sourceScheme = new TextLine( new Fields( "line" ) );
    Tap source = new Hfs( sourceScheme, input );

    //REPORT1 SINK
    Scheme report1SinkScheme = new TextDelimited( Fields.ALL, ",","\"" );
    Tap report1Sink = new Hfs( report1SinkScheme, output1, SinkMode.REPLACE );

    //REPORT2 SINK
    Scheme report2SinkScheme = new TextDelimited( Fields.ALL, ",","\"" );
    Tap report2Sink = new Hfs( report2SinkScheme, output2, SinkMode.REPLACE );

    //INITIAL FUNCTIONS
    Pipe firstPipe = new Pipe("firstPipe");
    firstPipe = new Each(firstPipe, new Fields("line"), functionA);
    firstPipe = new Each(firstPipe, functionB, Fields.ALL);

    //REPORT1 FUNCTION
    report1Pipe = new Each(firstPipe, Fields.ALL, function1, Fields.RESULTS);

    //REPORT2 FUNCTION
    report2Pipe = new Each(firstPipe, Fields.ALL, function2, Fields.RESULTS);

    //CONNECT FLOW PARTS
    FlowDef flowDef = new FlowDef()
    .setName("report-flow")
    .addSource(firstPipe, source)
    .addSink(report1Pipe, report1Sink)
    .addSink(report2Pipe, report2Sink);

    new HadoopFlowConnector( properties ).connect( flowDef ).complete();

Currently this is giving me the error "java.lang.IllegalArgumentException: cannot add duplicate sink: firstPipe" but even after messing around with it for a while I get a variety of other issues to do with the flow set up.

Is it possible for someone to explain how to construct a flow of this form (one source, two sinks)? Do I need to create a Cascade instead? Or do I need an intermediate sink to hold the data before I split?

Please help!

Answer 1

You can use the split pattern as mentioned in the Cascading documentation. Here's an example:

public static void main(String[] args) {
    // source and sink
    Scheme sourceScheme = new TextLine(new Fields("line"));
    Tap source = new FileTap(sourceScheme, args[0]);

    Fields sinkFields = new Fields("word", "count");
    Scheme sinkScheme = new TextLine(sinkFields, sinkFields);
    Tap sink_one = new FileTap(sinkScheme, "out-one.txt");
    Tap sink_two = new FileTap(sinkScheme, "out-two.txt");

    // the pipe assembly
    Pipe assembly = new Pipe("wordcount");

    String regex = "\\w+";
    Function function = new RegexGenerator(new Fields("word"), regex);
    assembly = new Each(assembly, new Fields("line"), function);

    Aggregator count = new Count(new Fields("count"));

    // ...split into two pipes
    Pipe countOne = new Pipe("count-one", assembly);
    countOne = new GroupBy(countOne, new Fields("word"));
    countOne = new Every(countOne, count);

    Pipe countTwo = new Pipe("count-two", assembly);
    countTwo = new GroupBy(countTwo, new Fields("word"));
    countTwo = new Every(countTwo, count);

    // create the flow
    final List<Pipe> pipes = new ArrayList<Pipe>(2);
    pipes.add(countOne);
    pipes.add(countTwo);

    final Map<String, Tap> sinks = new HashMap<String, Tap>();
    sinks.put("count-one", sink_one);
    sinks.put("count-two", sink_two);

    FlowConnector flowConnector = new LocalFlowConnector();
    Flow flow = flowConnector.connect(source, sinks, pipes);

    flow.complete();
}