Github user fhussonnois commented on a diff in the pull request:

    https://github.com/apache/storm/pull/827#discussion_r45238310
  
    --- Diff: 
external/storm-cassandra/src/main/java/org/apache/storm/cassandra/Murmur3StreamGrouping.java
 ---
    @@ -0,0 +1,89 @@
    +/**
    + * 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.storm.cassandra;
    +
    +import backtype.storm.generated.GlobalStreamId;
    +import backtype.storm.grouping.CustomStreamGrouping;
    +import backtype.storm.task.WorkerTopologyContext;
    +import backtype.storm.topology.FailedException;
    +import com.google.common.annotations.VisibleForTesting;
    +import com.google.common.collect.Lists;
    +import com.google.common.hash.Hashing;
    +
    +import java.io.ByteArrayOutputStream;
    +import java.io.DataOutputStream;
    +import java.io.IOException;
    +import java.util.List;
    +
    +/**
    + *
    + * Simple {@link backtype.storm.grouping.CustomStreamGrouping} that uses 
Murmur3 algorithm to choose the target task of a tuple.
    + *
    + * This stream grouping may be used to optimise writes to Apache Cassandra.
    + */
    +public class Murmur3StreamGrouping implements CustomStreamGrouping {
    --- End diff --
    
    Yes, that's right! Actually, I didn't even noticed there is no method like 
this on component : customGrouping(componentId, customStreamGrouping, 
fields...).
    
    So, one solution could be to pass the indexes of the the partition keys as 
follows : 
    myBolt.customGrouping("comp", new Murmur3StreamGrouping(0,1)) ?


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