Lianet Magrans created KAFKA-19259:
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Summary: 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
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
This needs more investigation to fully understand if it's indeed something in
the fetch path or something else)
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