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Posted to github@beam.apache.org by GitBox <gi...@apache.org> on 2022/03/15 22:21:30 UTC
[GitHub] [beam] dmitryor opened a new pull request #17096: [BEAM-14111] Increase timeout for data handover in KafkaReader's internal queue
dmitryor opened a new pull request #17096:
URL: https://github.com/apache/beam/pull/17096
Beam has two KafkaIO source implementations now:
* a modern one implemented as a Splittable DoFn (SDF), and
* a (deprecated) legacy one implemented as an SDF wrapper over an UnboundedSource and KafkaUnboundedReader classes.
O found that the legacy KafkaIO source can not provide good throughput when the latency of calls to Kafka [Consumer.poll|https://github.com/apache/beam/blob/master/sdks/java/io/kafka/src/main/java/org/apache/beam/sdk/io/kafka/KafkaUnboundedReader.java#L523] becomes high. The degradation is very sharp: a pipeline that drops elements immediately after reading them from source was only able to read about 100-1000 qps per Kafka partition. The Kafka cluster was overprovisioned but was in a remote network and had poll latency about 30ms.
The cause of throughput degradation is poor choice of the [RECORDS_DEQUEUE_POLL_TIMEOUTT|https://github.com/apache/beam/blob/master/sdks/java/io/kafka/src/main/java/org/apache/beam/sdk/io/kafka/KafkaUnboundedReader.java#L334-L335] set too low, it should be longer than any reasonable expected Kafka poll latency. This is what's happening otherwise:
* consumerPollLoop fetches data bundle from Kafka via poll() and offers it to the avaliableRecordsQueue
* message processing loop fetches bundle from avaliableRecordsQueue and unblocks the consumerPollLoop
* consumerPollLoop calls poll() again
* message processing loop completes processing the bundle BEFORE the poll() call above completes, and tries to fetch next bundle from avaliableRecordsQueue.
* fetch from avaliableRecordsQueue has a very short timeout (10ms) and if it expires before the pending poll() in the consumerPollLoop completes the message processing loop will believe there's no fresh data in Kafka and exit. All the time until the message processing loop is rescheduled is wasted.
R: @lukecwik
------------------------
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