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https://issues.apache.org/jira/browse/KAFKA-17503?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Matthias J. Sax updated KAFKA-17503:
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Component/s: clients
consumer
> The poll-idle-ratio-avg consumer metric is calculated incorrectly
> -----------------------------------------------------------------
>
> Key: KAFKA-17503
> URL: https://issues.apache.org/jira/browse/KAFKA-17503
> Project: Kafka
> Issue Type: Bug
> Components: clients, consumer
> Affects Versions: 3.8.0
> Reporter: Stig Rohde Døssing
> Assignee: Stig Rohde Døssing
> Priority: Minor
>
> The poll-idle-ratio-avg metric is supposed to calculate the fraction of time
> a thread spends inside KafkaConsumer.poll, indicating that the thread is
> waiting for Kafka rather than processing records.
> As
> [KIP-517|https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=127406453#KIP517:Addconsumermetricstoobserveuserpollbehavior-poll-idle-ratio-avg]
> says, the fraction is supposed to be "time-inside-poll/total-time".
> The metric's computation is slightly off, because the total time ends up
> being slightly too large, because it actually covers one full poll interval,
> plus the time spent in the latest poll call.
> To give an example say that a thread consistently spends 10 ms in poll, and
> 10 ms outside poll. We would expect a fraction of 0.5. But the metric as
> implemented calculates something slightly different.
> At time 0, we enter the first poll, setting pollStartMs to 0.
> At time 10, we exit the first poll, registering a meaningless value with the
> metric.
> At time 20, we enter the second poll, setting pollStartMs to 20, and setting
> timeSinceLastPollMs to 20.
> At time 30, we exit the second poll. The calculation we get is
> {code}pollTimeMs / (pollTimeMs + timeSinceLastPollMs){code} which in this
> case is {code}10 / (10 + 20)=0.33{code}
> This slightly wrong answer is because the divisor covers a larger period of
> time than the poll interval.
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