[
https://issues.apache.org/jira/browse/KAFKA-8421?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16858616#comment-16858616
]
Andrew Olson commented on KAFKA-8421:
-------------------------------------
It would be helpful to design and build a stress test harness for exhaustive
verification of this, since it seems like quite complex and critical
functionality. We could embark on that effort now, and use it to more fully
illustrate the weaknesses of the current behavior along with making sure we
have adequate logging in place for insight into what's going on deep in the
consumer internals.
> Allow consumer.poll() to return data in the middle of rebalance
> ---------------------------------------------------------------
>
> Key: KAFKA-8421
> URL: https://issues.apache.org/jira/browse/KAFKA-8421
> Project: Kafka
> Issue Type: Improvement
> Components: consumer
> Reporter: Guozhang Wang
> Priority: Major
>
> With KIP-429 in place, today when a consumer is about to send join-group
> request its owned partitions may not be empty, meaning that some of its
> fetched data can still be returned. Nevertheless, today the logic is strict:
> {code}
> if (!updateAssignmentMetadataIfNeeded(timer)) {
> return ConsumerRecords.empty();
> }
> {code}
> I.e. if the consumer enters a rebalance it always returns no data.
> As an optimization, we can consider letting consumers to still return
> messages that still belong to its owned partitions even when it is within a
> rebalance, because we know it is safe that no one else would claim those
> partitions in this rebalance yet, and we can still commit offsets if, after
> this rebalance, the partitions need to be revoked then.
> One thing we need to take care though is the rebalance timeout, i.e. when
> consumer's processing those records they may not call the next poll() in time
> (think: Kafka Streams num.iterations mechanism), which may leads to consumer
> dropping out of the group during rebalance.
--
This message was sent by Atlassian JIRA
(v7.6.3#76005)
