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| <h2 title="Interface StreamPartitioner" class="title">Interface StreamPartitioner<K,V></h2> |
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| <dl><dt><span class="strong">Type Parameters:</span></dt><dd><code>K</code> - the type of keys</dd><dd><code>V</code> - the type of values</dd></dl> |
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| <pre>public interface <span class="strong">StreamPartitioner<K,V></span></pre> |
| <div class="block">Determine how records are distributed among the partitions in a Kafka topic. If not specified, the underlying producer's |
| <code>DefaultPartitioner</code> will be used to determine the partition. |
| <p> |
| Kafka topics are divided into one or more <i>partitions</i>. Since each partition must fit on the servers that host it, so |
| using multiple partitions allows the topic to scale beyond a size that will fit on a single machine. Partitions also enable you |
| to use multiple instances of your topology to process in parallel all of the records on the topology's source topics. |
| <p> |
| When a topology is instantiated, each of its sources are assigned a subset of that topic's partitions. That means that only |
| those processors in that topology instance will consume the records from those partitions. In many cases, Kafka Streams will |
| automatically manage these instances, and adjust when new topology instances are added or removed. |
| <p> |
| Some topologies, though, need more control over which records appear in each partition. For example, some topologies that have |
| stateful processors may want all records within a range of keys to always be delivered to and handled by the same topology instance. |
| An upstream topology producing records to that topic can use a custom <i>stream partitioner</i> to precisely and consistently |
| determine to which partition each record should be written. |
| <p> |
| To do this, create a <code>StreamPartitioner</code> implementation, and when you build your topology specify that custom partitioner |
| when <a href="../../../../../org/apache/kafka/streams/processor/TopologyBuilder.html#addSink(java.lang.String,%20java.lang.String,%20org.apache.kafka.common.serialization.Serializer,%20org.apache.kafka.common.serialization.Serializer,%20org.apache.kafka.streams.processor.StreamPartitioner,%20java.lang.String...)"><code>adding a sink</code></a> |
| for that topic. |
| <p> |
| All StreamPartitioner implementations should be stateless and a pure function so they can be shared across topic and sink nodes.</div> |
| <dl><dt><span class="strong">See Also:</span></dt><dd><a href="../../../../../org/apache/kafka/streams/processor/TopologyBuilder.html#addSink(java.lang.String,%20java.lang.String,%20org.apache.kafka.common.serialization.Serializer,%20org.apache.kafka.common.serialization.Serializer,%20org.apache.kafka.streams.processor.StreamPartitioner,%20java.lang.String...)"><code>TopologyBuilder.addSink(String, String, org.apache.kafka.common.serialization.Serializer, |
| org.apache.kafka.common.serialization.Serializer, StreamPartitioner, String...)</code></a>, |
| <a href="../../../../../org/apache/kafka/streams/processor/TopologyBuilder.html#addSink(java.lang.String,%20java.lang.String,%20org.apache.kafka.streams.processor.StreamPartitioner,%20java.lang.String...)"><code>TopologyBuilder.addSink(String, String, StreamPartitioner, String...)</code></a></dd></dl> |
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| <td class="colFirst"><code><a href="http://docs.oracle.com/javase/7/docs/api/java/lang/Integer.html?is-external=true" title="class or interface in java.lang">Integer</a></code></td> |
| <td class="colLast"><code><strong><a href="../../../../../org/apache/kafka/streams/processor/StreamPartitioner.html#partition(K,%20V,%20int)">partition</a></strong>(<a href="../../../../../org/apache/kafka/streams/processor/StreamPartitioner.html" title="type parameter in StreamPartitioner">K</a> key, |
| <a href="../../../../../org/apache/kafka/streams/processor/StreamPartitioner.html" title="type parameter in StreamPartitioner">V</a> value, |
| int numPartitions)</code> |
| <div class="block">Determine the partition number for a record with the given key and value and the current number of partitions.</div> |
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| <a name="partition(java.lang.Object,java.lang.Object,int)"> |
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| </a><a name="partition(K, V, int)"> |
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| <h4>partition</h4> |
| <pre><a href="http://docs.oracle.com/javase/7/docs/api/java/lang/Integer.html?is-external=true" title="class or interface in java.lang">Integer</a> partition(<a href="../../../../../org/apache/kafka/streams/processor/StreamPartitioner.html" title="type parameter in StreamPartitioner">K</a> key, |
| <a href="../../../../../org/apache/kafka/streams/processor/StreamPartitioner.html" title="type parameter in StreamPartitioner">V</a> value, |
| int numPartitions)</pre> |
| <div class="block">Determine the partition number for a record with the given key and value and the current number of partitions.</div> |
| <dl><dt><span class="strong">Parameters:</span></dt><dd><code>key</code> - the key of the record</dd><dd><code>value</code> - the value of the record</dd><dd><code>numPartitions</code> - the total number of partitions</dd> |
| <dt><span class="strong">Returns:</span></dt><dd>an integer between 0 and <code>numPartitions-1</code>, or <code>null</code> if the default partitioning logic should be used</dd></dl> |
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