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https://issues.apache.org/jira/browse/KAFKA-4429?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15791620#comment-15791620
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Kevin Conaway commented on KAFKA-4429:
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I think it may be worth rethinking how the metrics are collected and
represented. Currently, the return type for the`Measurable#measure` method is
a primitive `double` which means that a value must be present. For stat values
that use Min and Max (like records-lag), this means that they default to
positive or negative infinity as the case may be.
In these two cases, the infinity values are used to represent the absence of a
real value. IMO, when there is no value we should return `Null` as most
reporting / metrics systems can handle null. I know that Graphite cannot
properly handle infinity values but I can't speak for other systems.
[~junrao] who is the right person to talk to about this?
This is also related to KAFKA-3241
> records-lag should be zero if FetchResponse is empty
> ----------------------------------------------------
>
> Key: KAFKA-4429
> URL: https://issues.apache.org/jira/browse/KAFKA-4429
> Project: Kafka
> Issue Type: Improvement
> Reporter: Dong Lin
> Assignee: Dong Lin
>
> In Fetcher we record records-lag in terms of number of records for any
> partition. Currently this metric value is updated only if number of parsed
> records is not empty. This means that if consumer has already fully caught up
> and there is no new data into the topic, this metric's value will be negative
> infinity and users can not rely on this metric to know if their consumer has
> caught up.
> We can fix this problem by assuming the lag is zero is FetchResponse is empty.
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