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From "Eno Thereska (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (KAFKA-4405) Kafka consumer improperly send prefetch request
Date Thu, 01 Dec 2016 09:41:58 GMT

    [ https://issues.apache.org/jira/browse/KAFKA-4405?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15711481#comment-15711481
] 

Eno Thereska commented on KAFKA-4405:
-------------------------------------

[~guozhang] Ignore previous comment, I was testing by mistake with max.poll.records=1000 today.
The PR is still showing benefits for max.poll.records=1

> 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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