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Change the behavior of the default partitioner in the key = null case. Choose the “sticky” partition for the given topic. The “sticky” partition is changed when the record accumulator is allocating a new batch for a topic on a given partition.

Remove testRoundRobinWithUnavailablePartitions() and testRoundRobin() since the round robin functionality of the partitioner has been removed.

Compatibility, Deprecation, and Migration Plan

• No compatibility, deprecation, migration plan required.Tests for the round robin partitioner and round robin behavior will be removed immediately.
• Users can continue to use their own partitioners--if they want to implement a sticky partitioner, they can use the onNewBatch(String topic, Cluster cluster) method to implement the feature, if they don’t want to use the feature, behavior will be the same.
• Existing users of the default partitioner for non-keyed, not set partitioned values should see either the same or decreased latency and cpu usage

Test Results

Testing the performance for this partitioner was done through the trogdor ProduceBench test. Modifications were made to allow for non-keyed, non-partitioned values as well as the ability to prevent batches from being flushed by the throttle. Besides waiting on linger.ms and filling the batch, a batch can be sent through a flush.Tests were done with and without flushing.

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