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https://issues.apache.org/jira/browse/BEAM-14111?focusedWorklogId=741922&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-741922
]
ASF GitHub Bot logged work on BEAM-14111:
-----------------------------------------
Author: ASF GitHub Bot
Created on: 15/Mar/22 22:21
Start Date: 15/Mar/22 22:21
Worklog Time Spent: 10m
Work Description: 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
------------------------
- [ ] [**Choose
reviewer(s)**](https://beam.apache.org/contribute/#make-your-change) and
mention them in a comment (`R: @username`).
- [ ] Format the pull request title like `[BEAM-XXX] Fixes bug in
ApproximateQuantiles`, where you replace `BEAM-XXX` with the appropriate JIRA
issue, if applicable. This will automatically link the pull request to the
issue.
- [ ] Update `CHANGES.md` with noteworthy changes.
- [ ] If this contribution is large, please file an Apache [Individual
Contributor License Agreement](https://www.apache.org/licenses/icla.pdf).
See the [Contributor Guide](https://beam.apache.org/contribute) for more
tips on [how to make review process
smoother](https://beam.apache.org/contribute/#make-reviewers-job-easier).
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Issue Time Tracking
-------------------
Worklog Id: (was: 741922)
Remaining Estimate: 0h
Time Spent: 10m
> Legacy (SDF wrapper-based) KafkaIO reader degrades when Kafka poll latency is
> hign
> ----------------------------------------------------------------------------------
>
> Key: BEAM-14111
> URL: https://issues.apache.org/jira/browse/BEAM-14111
> Project: Beam
> Issue Type: Improvement
> Components: io-java-kafka
> Reporter: Dmitry Orlovsky
> Priority: P2
> Time Spent: 10m
> Remaining Estimate: 0h
>
> 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.
> We 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.
> First problem that may be addressed in the scope of this bug is that there's
> very little visibility into the Kafka source now. We had to add extra logging
> to understand the issue with the pipeline above, or even see the poll latency.
> We believe that the cause of throughput degradation is poor choice of the
> [RECORDS_DEQUEUE_POLL_TIMEOUT and
> RECORDS_ENQUEUE_POLL_TIMEOUT|https://github.com/apache/beam/blob/master/sdks/java/io/kafka/src/main/java/org/apache/beam/sdk/io/kafka/KafkaUnboundedReader.java#L334-L335]
> especially the former one which is now 10ms.
> These are timeouts for popping and pushing elements from/to the
> [availableRecordsQueue
> |https://github.com/apache/beam/blob/master/sdks/java/io/kafka/src/main/java/org/apache/beam/sdk/io/kafka/KafkaUnboundedReader.java#L343].
> This is a synchronous queue (i.e. blocking, without buffering) used to hand
> records fetched from Kafka between two loops:
> * The
> [consumerPollLoop|https://github.com/apache/beam/blob/master/sdks/java/io/kafka/src/main/java/org/apache/beam/sdk/io/kafka/KafkaUnboundedReader.java#L515]
> that polls data via a Kafka Consumer if there's no pending data already, and
> offers it to the availableRecordsQueue otherwise. It also does offset
> checkpointing but this is irrelevant to our case.
> * The beam UnboundedSourceAsSDFWrapperFn message processing loop. It's a bit
> complicated, but the important part is that it would call the [nextBatch
> function|https://github.com/apache/beam/blob/master/sdks/java/io/kafka/src/main/java/org/apache/beam/sdk/io/kafka/KafkaUnboundedReader.java#L573]
> repeatedly until an attempt to [fetch an element from the
> avaliableRecordsQueue|https://github.com/apache/beam/blob/master/sdks/java/io/kafka/src/main/java/org/apache/beam/sdk/io/kafka/KafkaUnboundedReader.java#L580]
> times out. After the timeout, it returns the control to the worker and it
> may take relatively long time until the loop is scheduled again.
> This is what we think is happening when the poll latency is high:
> * 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.
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