Chi-Hsuan Huang created HDDS-16611:
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             Summary: Use MutableGaugeLong for numVolumes, numBuckets and 
numKeys in OMMetrics
                 Key: HDDS-16611
                 URL: https://issues.apache.org/jira/browse/HDDS-16611
             Project: Apache Ozone
          Issue Type: Bug
          Components: Ozone Manager
            Reporter: Chi-Hsuan Huang
            Assignee: Chi-Hsuan Huang


{{OMMetrics}} declares {{numVolumes}}, {{numBuckets}} and {{numKeys}} as 
{{MutableCounterLong}}, but they behave like gauges. They are decremented with 
{{incr\(\-1\)}}, and {{setNum\*\(\)}} emulates a set via {{incr\(val \- 
oldVal\)}}. This has been the case since HDDS\-816.

The JMX values are correct, but {{/prom}} exports these metrics as {{# TYPE 
counter}}. Prometheus treats any decrease in a counter as a reset. So the _Key 
Creation Rate_ panel in the Memory Consumption dashboard, which uses 
{{rate\(om\_metrics\_num\_keys\[1m\]\)}}, reports inflated values whenever keys 
are deleted.

HDDS\-10597 fixed the same pattern in {{SafeModeMetrics}}.

Proposed changes:
\- Switch the three fields to {{MutableGaugeLong}} and use {{set\(\)}} in 
{{setNumVolumes}}, {{setNumBuckets}} and {{setNumKeys}}.
\- Update {{TestOmMetrics}} to read these values with {{getLongGauge}} instead 
of {{getLongCounter}}.
\- Update the Key Creation Rate panel to use {{deriv\(\)}}, or 
{{rate\(om\_metrics\_num\_key\_commits\[1m\]\)}}.

Metric names in {{/jmx}} and {{/prom}} stay the same.





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