THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
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Lot of times, users want to send a record to more than one partition on the sink topic. Currently, if a user wants to replicate a message into N partitions, the only way of doing that is to replicate the message N times and then plug-in a custom partitioner to write the message N times into N different partitions. Since this seems to be a common requirement for users, this KIP aims to make this process simpler.
Public Interfaces
A new abstract class called MultiCastStreamPartitioner would be added extending StreamPartitioner interface which would allow returning a List of integers indicating the partitions to which the given record should be multi-casted to. Note that partition method is marked final throwing an UnsupportedOperationException as otherwise the child classes can supply both which can lead to confusion on which one to choose. Also note that, if the implementor happens to return all the partitions for the topic, then this effectively becomes broadcasting the record to all the partitionsThe StreamPartitioner method would have a new method added called partitions() and the current partition() method would be marked as deprecated. The partitions() method would be marked as default within which it would invoke partitions() method and construct a singleton list out of it. Here's how the interface would look like now:
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import java.util.List;
public abstract class MultiCastStreamPartitioner<K, V> implements StreamPartitioner<K, V>{ public interface StreamPartitioner<K, V> {
@Override/**
public * finalDetermine Integer partition(String topic, K key, V value, int numPartitions) {
throw new UnsupportedOperationException();
}
the partition number for a record with the given key and value and the current number of partitions.
*
* @param topic the topic name this record is sent to
* @param key the key of the record
* @param value the value of the record
* @param numPartitions the total number of partitions
* @return an integer between 0 and {@code numPartitions-1}, or {@code null} if the default partitioning logic should be used
*/
@Deprecated
Integer partition(String topic, K key, V value, int numPartitions);
/**
* Determine the List of partition numbers to which a record, with the given key and value and the current number
* of partitions, should be multi-casted to. Note that returning a single valued list with value -1 is a shorthand
* for broadcasting the record to all the partitions of the topic.
*
* @param topic the topic name this record is sent to
* @param key the key of the record
* @param value the value of the record
* @param numPartitions the total number of partitions
* @return a List of integers between 0 and {@code numPartitions-1}, or [-1] if null would mean a broadcast to all partitions
* while an empty list would mean the record would shouldnot be pushedsent to allany partitions.
* the partitions of the topic.
*/
publicdefault abstract List<Integer> partitions(String topic, K key, V value, int numPartitions) {
return Collections.singletonList(partition(topic, key, value, numPartitions));
} |
Proposed Changes
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}
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Proposed Changes
- RecordCollector and it's implementation RecordCollectorImpl has the method which accepts a StreamPartitioner object and pushes it to the partitions returned by the partition method. Since the users would be passing in an object which is a child of MultiCaseStreamPartitioner class, the send method would also check that and once the partitions are returned, send to all partitions one by one. Here's the code snipper for the same:This is the core piece of logic which would allow multi/broadcasting records. Here are the high level changes. Note that when the
partitions()method return an empty list meaning we won't send the record to any partition, we would also be updating the droppedRecordsSensor.Code Block language java @Override public <K, V> void send(final String topic, final K key, final V value, final Headers headers, final Long timestamp, final Serializer<K> keySerializer, final Serializer<V> valueSerializer, final StreamPartitioner<? super K, ? super V> partitioner) { Integer partition = null; final List<Integer> multicastPartitions; if (partitioner != null) { final List<PartitionInfo> partitions; try { partitions = streamsProducer.partitionsFor(topic); } catch (final TimeoutException timeoutException) { log.warn("Could not get partitions for topic {}, will retry", topic); // re-throw to trigger `task.timeout.ms` throw timeoutException; } catch (final KafkaException fatal) { // here we cannot drop the message on the floor even if it is a transient timeout exception, // so we treat everything the same as a fatal exception throw new StreamsException("Could not determine the number of partitions for topic '" + topic + "' for task " + taskId + " due to " + fatal.toString(), fatal ); } if (partitions.size() > 0) { multicastPartitions = partitioner.partitions(topic, key, ifvalue, (partitioner instanceof MultiCastStreamPartitionerpartitions.size()); if (multicastPartitions.isEmpty()) { log.info("Not sending multicastPartitions = ((MultiCastStreamPartitioner<? super K, ? super V>) partitioner).partitions(topic, key, value, partitions.size());the record to any partition"); droppedRecordsSensor.record(); } else { forif (intmulticastPartitions p:== multicastPartitionsnull) { send(topic, key, value, headers, p, timestamp, keySerializer, valueSerializer); // Broadcast to all partitions multicastPartitions return= partitions.stream().map(PartitionInfo::partition).collect(Collectors.toList()); } } else for (int p: multicastPartitions) { partition = partitioner.partitionsend(topic, key, value, partitions.size()), headers, p, timestamp, keySerializer, valueSerializer); } } } else { throw new StreamsException("Could not get partition information for topic " + topic + " for task " + taskId + ". This can happen if the topic does not exist."); } } else { send(topic, key, value, headers, partitionnull, timestamp, keySerializer, valueSerializer); } } } - StreamPartitioner is also used in FK-join and Interactive queries. The invocation of
partition()would be replaced bypartitions()and a runtime check would be added to ensure that the returned list is singleton.
Compatibility, Deprecation, and Migration Plan
Since we are adding a new abstract class with no provision of overriding partition method in StreamPartitioner, this should keep the current usages of StreamPartitioner interface backward-compatible. No deprecation/migration plan needed as well.
This KIP deprecates partition() method in StreamPartitioner . Here is what we would be doing as part of the same:
- StreamPartitioner is also used in FK-join and Interactive queries. The invocation of
partition()would be replaced bypartitions()and a runtime check would be added to ensure that the returned list is singleton. - Adding sufficient logging
Rejected Alternatives
- extend to() / addSink() with a "broadcast" option/config in KafkaStreams.
- add toAllPartitions() / addBroadcastSink() methods in KafkaStreams.
- allow StreamPartitioner to return `-1` for "all partitions"
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- Adding a separate class to handle multi casting.