ysysberserk created KAFKA-4405:
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             Summary: 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.

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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