Will James created KAFKA-8950:
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Summary: KafkaConsumer stops fetching
Key: KAFKA-8950
URL: https://issues.apache.org/jira/browse/KAFKA-8950
Project: Kafka
Issue Type: Bug
Components: clients
Affects Versions: 2.3.0
Environment: linux
Reporter: Will James
*Summary*
We have a KafkaConsumer consuming from a single partition with
enable.auto.commit set to true.
Very occasionally, the consumer goes into a broken state. It returns no records
from the broker with every poll, and from most of the Kafka metrics in the
consumer it looks like it is fully caught up to the end of the log.
We see that we are long polling for the max poll timeout, and that there is
zero lag. In addition, we see that the heartbeat rate stays unchanged from
before the issue begins (so the consumer stays a part of the consumer group).
In addition, from looking at the __consumer_offsets topic, it is possible to
see that the consumer is committing the same offset on the auto commit
interval, however, the offset does not move, and the lag from the broker's
perspective continues to increase.
The issue is only resolved by restarting our application (which restarts the
KafkaConsumer instance).
>From a heap dump of an application in this state, I can see that the Fetcher
>is in a state where it believes there are nodesWithPendingFetchRequests.
However, I can see the state of the fetch latency sensor, specifically, the
fetch rate, and see that the samples were not updated for a long period of time
(actually, precisely the amount of time that the problem in our application was
occurring, around 50 hours - we have alerting on other metrics but not the
fetch rate, so we didn't notice the problem until a customer complained).
In this example, the consumer was processing around 40 messages per second,
with an average size of about 10kb, although most of the other examples of this
have happened with higher volume (250 messages / second, around 23kb per
message on average).
I have spent some time investigating the issue on our end, and will continue to
do so as time allows, however I wanted to raise this as an issue because it may
be affecting other people.
Please let me know if you have any questions or need additional information. I
doubt I can provide heap dumps unfortunately, but I can provide further
information as needed.
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