Apache Storm发出DirectDirect问题

Question

I am new to Apache Storm. I was going thru the Toppology direct grouping example. My execute method :

public void execute(Tuple input) {
        String sentence = input.getString(0);
        String[] words = sentence.split(" ");
        for (String word : words) {
            word = word.trim();
            if (!word.isEmpty()) {
                word = word.toLowerCase();
                // Emit the word
                List a = new ArrayList();
                a.add(input);
                collector.emitDirect(getWordCountIndex(word),new Values(word));
            }
        }
        // Acknowledge the tuple
        collector.ack(input);
    }
public Integer getWordCountIndex(String word) { 
        word = word.trim().toUpperCase(); 
        if(word.isEmpty())
        return 0; 
        else{
            System.out.println(word +"------"+Character.getNumericValue(word.charAt(0)) % 13);
        return Character.getNumericValue(word.charAt(0)) % 13;
        }
    }

what I observed was getWordCountIndex() value if more than 10 or 0 it is not being counted by the counter bolt. However execute does group tuples so that all words that start with the same letter will be received by the same bolt.

Can someone please explain what is going on here. I checked the documentation not much help.

Thanks, Amit

Answer 1

referred from https://storm.apache.org/documentation/Concepts.html

Direct grouping: This is a special kind of grouping. A stream grouped this way means that the producer of the tuple decides which task of the consumer will receive this tuple. Direct groupings can only be declared on streams that have been declared as direct streams. Tuples emitted to a direct stream must be emitted using one of the [emitDirect](/javadoc/apidocs/backtype/storm/task/OutputCollector.html#emitDirect(int, int, java.util.List) methods. A bolt can get the task ids of its consumers by either using the provided TopologyContext or by keeping track of the output of the emit method in OutputCollector (which returns the task ids that the tuple was sent to).

So Character.getNumericValue(word.charAt(0)) % 13 means you need to have 13 tasks for word count bolt. otherwise the data will not be accepted. My guess is you are using 10 tasks for the bolt.