Lorenzo Alberton created KAFKA-761:
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Summary: Fetch request randomly returns 0 bytes when there's still
data in the log
Key: KAFKA-761
URL: https://issues.apache.org/jira/browse/KAFKA-761
Project: Kafka
Issue Type: Bug
Components: consumer
Affects Versions: 0.7.2
Environment: centos 6
Reporter: Lorenzo Alberton
Assignee: Neha Narkhede
I can't track the bug down in the code, but the behaviour has been hitting us
for quite some time (on Kafka 0.7.2): sometimes, a new Simple Consumer object,
on a new Fetch Request, returns an empty byte buffer (or a number of bytes
considerably smaller than the buffer size), even if there's more data on disk.
This happens randomly, with no errors, at different offsets in the same topic.
Different consumer groups processing the same topic might get stuck at
different offsets.
There seems to be no correlation between empty responses and the offset, or the
buffer size, or the log file size. At first we thought it only happened when
reaching the end of a log file, before jumping to the next file, but it doesn't
seem to be the case. It often happens in the middle of a file.
Simply retrying the Fetch Request multiple times works quite reliably, after 2
or 3 empty fetches the consumer eventually gets unstuck (we check the size of
the queue to see if there's more data before retrying).
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