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https://issues.apache.org/jira/browse/KAFKA-12478?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17557576#comment-17557576
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Guozhang Wang commented on KAFKA-12478:
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Thanks [~hudeqi], I will take a look at the KIP.
> Consumer group may lose data for newly expanded partitions when add
> partitions for topic if the group is set to consume from the latest
> ---------------------------------------------------------------------------------------------------------------------------------------
>
> Key: KAFKA-12478
> URL: https://issues.apache.org/jira/browse/KAFKA-12478
> Project: Kafka
> Issue Type: Improvement
> Components: clients
> Affects Versions: 3.1.1
> Reporter: hudeqi
> Priority: Blocker
> Labels: kip-842
> Attachments: safe-console-consumer.png, safe-consume.png,
> safe-produce.png, trunk-console-consumer.png, trunk-consume.png,
> trunk-produce.png
>
> Original Estimate: 1,158h
> Remaining Estimate: 1,158h
>
> This problem is exposed in our product environment: a topic is used to
> produce monitoring data. *After expanding partitions, the consumer side of
> the business reported that the data is lost.*
> After preliminary investigation, the lost data is all concentrated in the
> newly expanded partitions. The reason is: when the server expands, the
> producer firstly perceives the expansion, and some data is written in the
> newly expanded partitions. But the consumer group perceives the expansion
> later, after the rebalance is completed, the newly expanded partitions will
> be consumed from the latest if it is set to consume from the latest. Within a
> period of time, the data of the newly expanded partitions is skipped and lost
> by the consumer.
> If it is not necessarily set to consume from the earliest for a huge data
> flow topic when starts up, this will make the group consume historical data
> from the broker crazily, which will affect the performance of brokers to a
> certain extent. Therefore, *it is necessary to consume these partitions from
> the earliest separately.*
>
> I did a test and the result is as attached screenshot. Firstly, set by
> producer and consumer "metadata.max.age.ms" are 500ms and 30000ms
> respectively.
> _trunk-console-consumer.png_ means to use the community version to start the
> consumer and set "latest".
> _trunk-produce.png_ means the data produced, "partition_count" means the
> number of partitions of the current topic, "message" means the digital
> content of the corresponding message, "send_to_partition_index" Indicates the
> index of the partition to which the corresponding message is sent. It can be
> seen that at 11:32:10, the producer perceives the expansion of the total
> partitions from 2 to 3, and writes the numbers 38, 41, and 44 into the newly
> expanded partition 2.
> _trunk-consume.png_ represents all the digital content consumed by the
> community version. You can see that 38 and 41 sent to partition 2 were not
> consumed at the beginning. Finally, after partition 2 was perceived, 38 and
> 41 were still not consumed. Instead, it has been consumed from the latest 44,
> so the two data of 38 and 41 are discarded.
>
> _safe-console-consumer.png_ means to use the fixed version to start the
> consumer and set "safe_latest".
> _safe-produce.png_ means the data produced. It can be seen that at 12:12:09,
> the producer perceives the expansion of the total partitions from 4 to 5, and
> writes the numbers 109 and 114 into the newly expanded partition 4.
> _safe-consume.png_ represents all the digital content consumed by the fixed
> version. You can see that 109 sent to partition 4 were not consumed at the
> beginning. Finally, after partition 4 was perceived,109 was consumed as the
> first data of partition 4. So the fixed version will not cause consumption to
> lose data under this condition.
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