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https://issues.apache.org/jira/browse/KAFKA-4402?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15793139#comment-15793139
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ASF GitHub Bot commented on KAFKA-4402:
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Github user yaojuncn closed the pull request at:
https://github.com/apache/kafka/pull/2128
> Kafka Producer's DefaultPartitioner is actually not round robin as said in
> the code comments "If no partition or key is present choose a partition in a
> round-robin fashion"
> ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------
>
> Key: KAFKA-4402
> URL: https://issues.apache.org/jira/browse/KAFKA-4402
> Project: Kafka
> Issue Type: Improvement
> Reporter: Jun Yao
> Priority: Minor
>
> From this code comments, it is said that Kafka client Producer's
> DefaultPartitioner will do round robin if "no partition or key is present",
> https://github.com/apache/kafka/blob/41e676d29587042994a72baa5000a8861a075c8c/clients/src/main/java/org/apache/kafka/clients/producer/internals/DefaultPartitioner.java#L34
> from the code it looks trying to do round robin as well, as it maintained a
> counter and try to increase it every time and then will decide which
> partition to go to;
> However the issue here is the counter is a global counter that is shared by
> all the topics, so it is actually not round robin per topic and sometimes
> caused unbalanced routing among different partitions.
> Although we can pass a custom implementation of interface
> "org.apache.kafka.clients.producer.Partitioner", it might be still good to
> make the default implementation true round robin as comment.
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