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https://issues.apache.org/jira/browse/FLINK-34554?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17860823#comment-17860823
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Martijn Visser commented on FLINK-34554:
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[~loserwang1024] I think that would require a discussion on the Dev mailing
list and potentially a FLIP, it would be great if you could start such a
discussion thread
> Using EXACTLY_ONCE with KafkaSink cause broker's OOM due to newly created
> transactionalId per checkpoint
> --------------------------------------------------------------------------------------------------------
>
> Key: FLINK-34554
> URL: https://issues.apache.org/jira/browse/FLINK-34554
> Project: Flink
> Issue Type: Improvement
> Components: Connectors / Kafka
> Affects Versions: 1.16.3, 1.17.2, 1.18.1
> Reporter: Hilmi Al Fatih
> Priority: Major
> Attachments: image (4).png, image (5).png,
> image-2024-03-16-17-17-16-152.png
>
>
> Flink version: 1.17.1
> Kafka Broker version: 2.7.1 * 4 GB heap memory for each
> Hi, We recently had an outage in our production system after we perform a
> Flink kafka-connector API upgrade. To give a brief context, our application
> is a simple kafka-to-kafka pipeline with minimal processing. We run in
> EXACTLY_ONCE mode, thus kafka transaction is involved.
> Our application runs with total around 350 sink subtask. Checkpoint period
> was set to 5 seconds to avoid blocking {{read_committed}} consumers too long.
> We recently performed an upgrade with the following details:
> Previous state:
> * Flink version: 1.14.4
> * Broker version: 2.7.1
> * kafka connector API: FlinkKafkaProducer
> Update to:
> * Flink version: 1.17.1
> * Broker version: 2.7.1
> * kafka connector API: KafkaSink
> Around 10 hours after the deployment, our kafka broker started to failing
> with OOM error. Heap dump entries are dominated by the ProducerStateEntry
> records.
> Our investigation leads to finding the total implementation change between
> FlinkKafkaProducer and KafkaSink.
> * KafkaSink generate different transactionalId for each checkpoint,
> * FlinkKafkaProducer uses constant set of transactionalId pool.
> With this behavior, KafkaSink seemed to exhaust our broker heap very fast and
> the ProducerStateEntry will only expire after
> [transactional.id.expiration.ms|http://transactional.id.expiration.ms/] ,
> which by default is set to 7 days.
> ([ref1|https://github.com/apache/kafka/blob/61dbce85d0d41457d81a4096ecaea049f3a4b3ae/core/src/main/scala/kafka/log/Log.scala#L677],
>
> [ref2|https://github.com/apache/kafka/blob/61dbce85d0d41457d81a4096ecaea049f3a4b3ae/core/src/main/scala/kafka/log/LogManager.scala#L268],
>
> [ref3|https://github.com/apache/kafka/blob/61dbce85d0d41457d81a4096ecaea049f3a4b3ae/core/src/main/scala/kafka/log/LogManager.scala#L1207])
> For our job, it means it creates roughly:
> * 10 hour running) 350 ids * 12 times/minute * 60 min/hour * 10 hour ~
> 2,520,000
> * 7 days) ~ 42mil entries.
> Attached below is the number of ProducerStateEntry entries of heap dump when
> it is OOM:
> * 505,000 (6.5%), in total it would be roughly ~ 7,000,000 entries.
> There are several things that come up in our mind to mitigate the drawbacks
> such as:
> * reduce the number of subtasks, so it reduces the number of transactionalId
> * Enlarge the checkpoint period to reduce the newly generated
> transactionalId rate.
> * Shorten
> [transactional.id.expiration.ms|http://transactional.id.expiration.ms/] to
> expire the unused transactionalId soon.
> * Increase the broker heap
> However, above mitigation might be too cumbersome and need careful tuning
> which harm our flexibility.In addition, due to the lack of maintaining
> lingering transaction state, TransactionAborter seems to abort old
> transaction naively. We might be accidentally (or purposefully) reuse the
> same transactionalIdPrefix and start the counter from 0. In that case, if the
> old transactionalId happens to have epoch >0, it will keep looping aborting
> the nonexistent transactions up to the latest checkpoint counter (which may
> be too big) and make the job stuck.
> Btw, I am aware that in Flink 2.0, you guys are putting a lot of effort on
> creating better integration with Kafka transaction
> ([FLIP-319|https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=255071710]).
> In FLIP-319, it mentions something about TID pooling. However, it is seem
> that there is no relevant page yet for it, so I wonder whether there are any
> concrete plan already that I can follow, or if there is something I can
> contribute to, I will be really happy to help.
>
>
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