Github user satishd commented on a diff in the pull request:
https://github.com/apache/storm/pull/827#discussion_r45177772
--- 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 --
@fhussonnois Cassandra should be partitioning rows based on partition key
on a row according to the configured partitioner. But here, the grouping is
done based on the hash generated on tuple values which may contain values other
than partition key. Can you elaborate on this? Pl add more details in java
doc.
It maybe helpful for users to have information about this grouping in
ReadMe.md.
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