Andreas Kohn created KAFKA-8850:
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Summary: fetch.min.bytes documentation could be misunderstood
Key: KAFKA-8850
URL: https://issues.apache.org/jira/browse/KAFKA-8850
Project: Kafka
Issue Type: Improvement
Components: documentation
Reporter: Andreas Kohn
The current documentation for `fetch.min.bytes` says:
> The minimum amount of data the server should return for a fetch request. _If
> insufficient data is available the request will wait for that much data to
> accumulate before answering the request._ The default setting of 1 byte means
> that fetch requests are answered as soon as a single byte of data is
> available or the fetch request times out waiting for data to arrive. Setting
> this to something greater than 1 will cause the server to wait for larger
> amounts of data to accumulate which can improve server throughput a bit at
> the cost of some additional latency.
The highlighted sentence made me believe that Kafka would start waiting, and
_as soon as enough data was available would stop waiting and return_. In
reality the behavior is that Kafka will check for enough data, and if there
isn't will wait the full `fetch.max.wait.ms` time.
I would propose rewording the sentence to make that clearer, for example:
"If insufficient data is available the request will wait for
`fetch.max.wait.ms` before answering the request."
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