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https://issues.apache.org/jira/browse/KAFKA-3627?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Liquan Pei reassigned KAFKA-3627:
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Assignee: Liquan Pei (was: Neha Narkhede)
> New consumer doesn't run delayed tasks while under load
> -------------------------------------------------------
>
> Key: KAFKA-3627
> URL: https://issues.apache.org/jira/browse/KAFKA-3627
> Project: Kafka
> Issue Type: Bug
> Components: consumer
> Affects Versions: 0.9.0.1
> Reporter: Rob Underwood
> Assignee: Liquan Pei
>
> If the new consumer receives a steady flow of fetch responses it will not run
> delayed tasks, which means it will not heartbeat or perform automatic offset
> commits.
> The main cause is the code that attempts to pipeline fetch responses and keep
> the consumer fed. Specifically, in KafkaConsumer::pollOnce() there is a
> check that skips calling client.poll() if there are fetched records ready
> (line 903 in the 0.9.0 branch of this writing). Then in
> KafkaConsumer::poll(), if records are returned it will initiate another fetch
> and perform a quick poll, which will send/receive fetch requests/responses
> but will not run delayed tasks.
> If the timing works out, and the consumer is consistently receiving fetched
> records, it won't run delayed tasks until it doesn't receive a fetch response
> during its quick poll. That leads to a rebalance since the consumer isn't
> heartbeating, and typically means all the consumed records will be
> re-delivered since the automatic offset commit wasn't able to run either.
> h5. Steps to reproduce
> # Start up a cluster with *at least 2 brokers*. This seems to be required to
> reproduce the issue, I'm guessing because the fetch responses all arrive
> together when using a single broker.
> # Create a topic with a good number of partitions
> #* bq. bin/kafka-topics.sh --zookeeper localhost:2181 --create --topic
> delayed-task-bug --partitions 10 --replication-factor 1
> # Generate some test data so the consumer has plenty to consume. In this
> case I'm just using uuids
> #* bq. for ((i=0;i<100;++i)) do; cat /proc/sys/kernel/random/uuid >>
> /tmp/test-messages; done
> #* bq. bin/kafka-console-producer.sh --broker-list localhost:9092 --topic
> delayed-task-bug < /tmp/test-messages
> # Start up a consumer with a small max fetch size to ensure it only pulls a
> few records at a time. The consumer can simply sleep for a moment when it
> receives a record.
> #* I'll attach an example in Java
> # There's a timing aspect to this issue so it may take a few attempts to
> reproduce
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