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https://issues.apache.org/jira/browse/FLINK-11912?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16808541#comment-16808541
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aitozi commented on FLINK-11912:
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Hi [~suez1224] , [~tzulitai]
I have tried to solve this bug in a very old flink version by tryRegister
metric for a time after the poll message from kafka as you did in the
experimental change you posted . But in production, I find there is also a
possibility that we can lose the per partition lag, because may be not all
partition lag metric are registered after a poll call, as i mentioned in
[FLINK-7945|https://github.com/apache/flink/pull/4935#issuecomment-348252535] .
> Expose per partition Kafka lag metric in Flink Kafka connector
> --------------------------------------------------------------
>
> Key: FLINK-11912
> URL: https://issues.apache.org/jira/browse/FLINK-11912
> Project: Flink
> Issue Type: New Feature
> Components: Connectors / Kafka
> Affects Versions: 1.6.4, 1.7.2
> Reporter: Shuyi Chen
> Assignee: Shuyi Chen
> Priority: Major
>
> In production, it's important that we expose the Kafka lag by partition
> metric in order for users to diagnose which Kafka partition is lagging.
> However, although the Kafka lag by partition metrics are available in
> KafkaConsumer after 0.10.2, Flink was not able to properly register it
> because the metrics are only available after the consumer start polling data
> from partitions. I would suggest the following fix:
> 1) In KafkaConsumerThread.run(), allocate a manualRegisteredMetricSet.
> 2) in the fetch loop, as KafkaConsumer discovers new partitions, manually add
> MetricName for those partitions that we want to register into
> manualRegisteredMetricSet.
> 3) in the fetch loop, check if manualRegisteredMetricSet is empty. If not,
> try to search for the metrics available in KafkaConsumer, and if found,
> register it and remove the entry from manualRegisteredMetricSet.
> The overhead of the above approach is bounded and only incur when discovering
> new partitions, and registration is done once the KafkaConsumer have the
> metrics exposed.
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