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https://issues.apache.org/jira/browse/KAFKA-3135?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15750082#comment-15750082
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Jeff Widman commented on KAFKA-3135:
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Can the tags on this issue be updated to note that it applies to 0.10.x
versions as well?
At least, that's what it seems from reading through the issue description.
> 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
> 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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