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https://issues.apache.org/jira/browse/KAFKA-19259?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17954402#comment-17954402
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Lianet Magrans commented on KAFKA-19259:
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Hey [~goyarpit], sorry I've been away but checked again and these are the exact
steps I follow and see the different pattern (repro now, on trunk):
1- ./bin/kafka-server-start.sh config/server.properties
2- bin/kafka-topics.sh --bootstrap-server localhost:9092 --create --topic t1
--partitions 6
3- while sleep 1; do echo $(uuidgen); done | bin/kafka-console-producer.sh
--bootstrap-server localhost:9092 --topic t1
4- bin/kafka-console-consumer.sh --topic t1 --bootstrap-server localhost:9092
--consumer-property group.protocol=classic --group cg1 --consumer-property
enable.auto.commit=false ==> ( here I see records continuously)
5- bin/kafka-console-consumer.sh --topic t1 --bootstrap-server localhost:9092
--consumer-property group.protocol=consumer --group cg1 --consumer-property
enable.auto.commit=false ==> ( here I see records in kind of batches, with
a delay in between. This is probably what leads to the spiky lag we also see
with the new consumer only, when describing the group with the command line
tool too)
I recorded a video of the output so you can see the pattern I refer too that we
need to understand.
[^console-consumer-classic-vs-consumer.mov]
I'll be looking into this in detail soon but hope this helps in the meantime.
Thanks for your help!
> Async consumer fetch intermittent delays on console consumer
> ------------------------------------------------------------
>
> Key: KAFKA-19259
> URL: https://issues.apache.org/jira/browse/KAFKA-19259
> Project: Kafka
> Issue Type: Bug
> Components: clients, consumer
> Affects Versions: 4.0.0
> Reporter: Lianet Magrans
> Assignee: Arpit Goyal
> Priority: Major
> Fix For: 4.1.0
>
> Attachments: console-consumer-classic-vs-consumer.mov
>
>
> We noticed that fetching with the kafka-console-consumer.sh tool using the
> new consumer shows some intermittent delays, that are not seen when running
> the same with the classic consumer. Note that I disabled auto-commit to
> isolate the delay, and from a first look seems to come from the
> fetchBuffer.awaitNonEmpty logic, that alternatively takes almost the full
> poll timeout (runs "fast", then "slow", and continues to alternate)
> [https://github.com/apache/kafka/blob/0b81d6c7802c1be55dc823ce51729f2c6a6071a7/clients/src/main/java/org/apache/kafka/clients/consumer/internals/AsyncKafkaConsumer.java#L1808]
>
> The difference in behaviour between the 2 consumers can be seen with this
> setup:
> * topic with 6 partitions (I tried with 1 partition first and didn't see the
> delay, then with 3 and 6 I could see it)
> * data populated in topic with producer sending generated uuids to the topic
> in while loop
> * run console consumer (asycn) no commit:
> bin/kafka-console-consumer.sh --topic t1 --bootstrap-server localhost:9092
> --consumer-property group.protocol=consumer --group cg1 --consumer-property
> enable.auto.commit=false
> Here we can notice the pattern that looks like batches, and custom logs on
> the awaitNonEmpty show it take the full poll timeout on alternate poll
> iterations.
> * run same but for classic consumer (consumer-property
> group.protocol=classic) -> not such pattern of intermittent delays
> Produce continuously (I used this)
> while sleep 1; do echo $(uuidgen); done | bin/kafka-console-producer.sh
> --bootstrap-server localhost:9092 --topic t1
> This needs more investigation to fully understand if it's indeed something in
> the fetch path or something else)
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