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https://issues.apache.org/jira/browse/KAFKA-3135?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Ewen Cheslack-Postava updated KAFKA-3135:
-----------------------------------------
    Affects Version/s: 0.10.1.0
                       0.9.0.1
                       0.10.0.0
                       0.10.0.1
                       0.10.1.1

> Unexpected delay before fetch response transmission
> ---------------------------------------------------
>
>                 Key: KAFKA-3135
>                 URL: https://issues.apache.org/jira/browse/KAFKA-3135
>             Project: Kafka
>          Issue Type: Bug
>    Affects Versions: 0.9.0.0, 0.10.1.0, 0.9.0.1, 0.10.0.0, 0.10.0.1, 0.10.1.1
>            Reporter: Jason Gustafson
>            Assignee: Jason Gustafson
>            Priority: Critical
>             Fix For: 0.10.2.0
>
>
> From the user list, Krzysztof Ciesielski reports the following:
> {quote}
> Scenario description:
> First, a producer writes 500000 elements into a topic
> Then, a consumer starts to read, polling in a loop.
> When "max.partition.fetch.bytes" is set to a relatively small value, each
> "consumer.poll()" returns a batch of messages.
> If this value is left as default, the output tends to look like this:
> Poll returned 13793 elements
> Poll returned 13793 elements
> Poll returned 13793 elements
> Poll returned 13793 elements
> Poll returned 0 elements
> Poll returned 0 elements
> Poll returned 0 elements
> Poll returned 0 elements
> Poll returned 13793 elements
> Poll returned 13793 elements
> As we can see, there are weird "gaps" when poll returns 0 elements for some
> time. What is the reason for that? Maybe there are some good practices
> about setting "max.partition.fetch.bytes" which I don't follow?
> {quote}
> The gist to reproduce this problem is here: 
> https://gist.github.com/kciesielski/054bb4359a318aa17561.
> After some initial investigation, the delay appears to be in the server's 
> networking layer. Basically I see a delay of 5 seconds from the time that 
> Selector.send() is invoked in SocketServer.Processor with the fetch response 
> to the time that the send is completed. Using netstat in the middle of the 
> delay shows the following output:
> {code}
> tcp4       0      0  10.191.0.30.55455      10.191.0.30.9092       ESTABLISHED
> tcp4       0 102400  10.191.0.30.9092       10.191.0.30.55454      ESTABLISHED
> {code}
> From this, it looks like the data reaches the send buffer, but needs to be 
> flushed.



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