[jira] [Commented] (KAFKA-7132) Consider adding faster form of rebalancing

["Stanislav Kozlovski (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KAFKA-7132?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16532545#comment-16532545 ] 

Stanislav Kozlovski commented on KAFKA-7132:
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The best way to consider this is to open a KIP and pass it to the mailing group for thorough discussion.
This is a good way to avoid lag but unfortunately will mess up every ordering guarantee.

> Consider adding faster form of rebalancing
> ------------------------------------------
>
>                 Key: KAFKA-7132
>                 URL: https://issues.apache.org/jira/browse/KAFKA-7132
>             Project: Kafka
>          Issue Type: Improvement
>          Components: consumer
>            Reporter: Richard Yu
>            Priority: Critical
>              Labels: performance
>
> Currently, when a consumer falls out of a consumer group, it will restart processing from the last checkpointed offset. However, this design could result in a lag which some users could not afford to let happen. For example, lets say a consumer crashed at offset 100, with the last checkpointed offset being at 70. When it recovers at a later offset (say, 120), it will be behind by an offset range of 50 (120 - 70). This is because the consumer restarted at 70, forcing it to reprocess old data. To avoid this from happening, one option would be to allow the current consumer to start processing not from the last checkpointed offset (which is 70 in the example), but from 120 where it recovers. Meanwhile, a new KafkaConsumer will be instantiated and start reading from offset 70 in concurrency with the old process, and will be terminated once it reaches 120. In this manner, a considerable amount of lag can be avoided, particularly since the old consumer could proceed as if nothing had happened. 



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