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https://issues.apache.org/jira/browse/CASSANDRA-6591?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13922755#comment-13922755
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Ian Barfield commented on CASSANDRA-6591:
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The "hit mva / rate mva" and "hit rate mva" as you define them are indeed very
different things. This is most likely intentional and I would say desirable.
The red line "hit rate mva" seems to be applying the idea of recency to a
metric that already has a recency window (in this case the window is 'all
time'). This strikes me as both unintuitive and unhelpful; after the metrics
have been going for a while it is unlikely to change very fast, and by making
it a moving average it will change even slower. You could easily have a 100%
miss ratio for several minutes and never see that line move. That seems to
defeat the purpose of having a "recent" hitRate metric.
As for EWMAs being 'comparable': I'm not certain on the exact mathematical
implications of dividing two estimates after sampling, but I strongly suspect
it would be more than accurate enough for this purpose.
> un-deprecate cache recentHitRate and expose in o.a.c.metrics
> ------------------------------------------------------------
>
> Key: CASSANDRA-6591
> URL: https://issues.apache.org/jira/browse/CASSANDRA-6591
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Reporter: Chris Burroughs
> Assignee: Chris Burroughs
> Priority: Minor
> Attachments: j6591-1.2-v1.txt, j6591-1.2-v2.txt, j6591-1.2-v3.txt
>
>
> recentHitRate metrics were not added as part of CASSANDRA-4009 because there
> is not an obvious way to do it with the Metrics library. Instead hitRate was
> added as an all time measurement since node restart.
> This does allow changes in cache rate (aka production performance problems)
> to be detected. Ideally there would be 1/5/15 moving averages for the hit
> rate, but I'm not sure how to calculate that. Instead I propose updating
> recentHitRate on a fixed interval and exposing that as a Gauge.
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