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https://issues.apache.org/jira/browse/KAFKA-2434?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14908997#comment-14908997
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Jun Rao commented on KAFKA-2434:
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[~andy_k], thanks for the patch. It seems the algorithm is following: during
the round-robin iteration of all the partitions, it just skips over consumers
not subscribing to a topic. While this seems to guarantee consistent
assignment, it doesn't seem to guarantee uniform distribution. For example,
consider the following case. There are 3 consumers c1, c2, and c3. c1 and c2
subscribe to topics t1, t2, and t3, and c3 subscribes to topic t1 only. Each
topic has 2 partitions. The algorithm will sort the partitions in the following
order: t1-p1, t2-p1, t3-p1, t1-p2, t2-p2, t3-p2, and iterate the consumers in
the order of c1, c2, c3. In the end, it seems that t1-p1, t3-p1, t2-p2 will be
assigned to c1 and t2-p1, t1-p2, t3-p2 will be assigned to c2, and c3 won't get
any partitions.
> remove roundrobin identical topic constraint in consumer coordinator (old API)
> ------------------------------------------------------------------------------
>
> Key: KAFKA-2434
> URL: https://issues.apache.org/jira/browse/KAFKA-2434
> Project: Kafka
> Issue Type: Sub-task
> Reporter: Andrew Olson
> Assignee: Andrew Olson
> Attachments: KAFKA-2434.patch
>
>
> The roundrobin strategy algorithm improvement made in KAFKA-2196 should be
> applied to the original high-level consumer API as well.
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