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https://issues.apache.org/jira/browse/KAFKA-9965?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17417479#comment-17417479
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Jon McEwen commented on KAFKA-9965:
-----------------------------------
I think I had something similar to the above initially, but it had thread
safety issues.
Here is my current WIP patch
[https://github.com/apache/kafka/pull/11326]
[~showuon] please could you help me with formatting? I can't find a gradle
task for formatting Java code.
Do you think a unit test based on the current call pattern from producer is
sufficient? I think there is another ticket open for creating integration
tests.
> Uneven distribution with RoundRobinPartitioner in AK 2.4+
> ---------------------------------------------------------
>
> Key: KAFKA-9965
> URL: https://issues.apache.org/jira/browse/KAFKA-9965
> Project: Kafka
> Issue Type: Bug
> Components: producer
> Affects Versions: 2.4.0, 2.5.0, 2.4.1
> Reporter: Michael Bingham
> Priority: Major
>
> {{RoundRobinPartitioner}} states that it will provide equal distribution of
> records across partitions. However with the enhancements made in KIP-480, it
> may not. In some cases, when a new batch is started, the partitioner may be
> called a second time for the same record:
> [https://github.com/apache/kafka/blob/2.4/clients/src/main/java/org/apache/kafka/clients/producer/KafkaProducer.java#L909]
> [https://github.com/apache/kafka/blob/2.4/clients/src/main/java/org/apache/kafka/clients/producer/KafkaProducer.java#L934]
> Each time the partitioner is called, it increments a counter in
> {{RoundRobinPartitioner}}, so this can result in unequal distribution.
> Easiest fix might be to decrement the counter in
> {{RoundRobinPartitioner#onNewBatch}}.
>
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