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https://issues.apache.org/jira/browse/KAFKA-4405?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15707215#comment-15707215
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ysysberserk commented on KAFKA-4405:
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Oh, I am sorry that I only read the code and did not notice that in
fetchablePartitions() the partition which has records is removed before sent a
prefetch.
So there is no such a big problem and current work flow is ok.
But we can still add check if total number of retained records is less than
max.poll.records before we call
fetcher.sendFetches().It will prevent useless call and save a lot of time.
> Kafka consumer improperly send prefetch request
> -----------------------------------------------
>
> Key: KAFKA-4405
> URL: https://issues.apache.org/jira/browse/KAFKA-4405
> Project: Kafka
> Issue Type: Bug
> Affects Versions: 0.10.0.1
> Reporter: ysysberserk
>
> Now kafka consumer has added max.poll.records to limit the count of messages
> return by poll().
> According to KIP-41, to implement max.poll.records, the prefetch request
> should only be sent when the total number of retained records is less than
> max.poll.records.
> But in the code of 0.10.0.1 , the consumer will send a prefetch request if it
> retained any records and never check if total number of retained records is
> less than max.poll.records..
> If max.poll.records is set to a count much less than the count of message
> fetched , the poll() loop will send a lot of requests than expected and will
> have more and more records fetched and stored in memory before they can be
> consumed.
> So before sending a prefetch request , the consumer must check if total
> number of retained records is less than max.poll.records.
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