[jira] [Commented] (KAFKA-3627) New consumer doesn't run delayed tasks while under load

["Rob Underwood (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KAFKA-3627?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15258963#comment-15258963 ] 

Rob Underwood commented on KAFKA-3627:
--------------------------------------

I've attached an example consumer in Java that often reproduces the issue, as well as the output from one such reproduction.

> 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
>         Attachments: DelayedTaskBugConsumer.java, kafka-3627-output.log
>
>
> 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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