[jira] [Created] (KAFKA-17954) Error getting oldest-iterator-open-since-ms from JMX

["Nicholas Telford (Jira)" <ji...@apache.org>]

Nicholas Telford created KAFKA-17954:
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             Summary: Error getting oldest-iterator-open-since-ms from JMX
                 Key: KAFKA-17954
                 URL: https://issues.apache.org/jira/browse/KAFKA-17954
             Project: Kafka
          Issue Type: Bug
          Components: streams
    Affects Versions: 3.8.1
            Reporter: Nicholas Telford


In [KIP-989|https://cwiki.apache.org/confluence/display/KAFKA/KIP-989%3A+Improved+StateStore+Iterator+metrics+for+detecting+leaks] we introduced a new metric, {{{}oldest-iterator-open-since-ms{}}}, which reports the timestamp that the oldest currently open KeyValueIterator was opened at.

However, if no iterators are currently open, this Gauge returns {{{}null{}}}.

When using the Prometheus {{JmxScraper}} to scrape this metric, its value is added to a {{{}ConcurrentHashMap{}}}, which does _not_ permit {{null}} values.

Consequently, on-scrape, we see this {{WARN}} log message:
{noformat}
Error getting JMX attribute 'oldest-iterator-open-since-ms' {noformat}
We should find some other way to report the absence of this metric that does not cause problems with {{{}ConcurrentHashMap{}}}.



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