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Kévin LOVATO commented on CASSANDRA-12876:
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I looked at the code as well and can't see an obvious way to have negative
values in decayingBuckets, even after a rescale(). Also, I noticed that the
time during which the metric is negative lasts for about 3 minutes and it goes
down under zero multiple times during this period of time (cf.
[^negative_mean_details.PNG]), where I would expect to see only one dip under
zero if it was caused by the rescale. Hope those details will put you in the
right direction.
> Negative mean write latency
> ---------------------------
>
> Key: CASSANDRA-12876
> URL: https://issues.apache.org/jira/browse/CASSANDRA-12876
> Project: Cassandra
> Issue Type: Bug
> Components: Observability
> Reporter: Kévin LOVATO
> Assignee: Per Otterström
> Attachments: negative_mean.png, negative_mean_details.PNG,
> negative_mean_periodicity.PNG
>
>
> The mean write latency returned by JMX turns negative every 30 minutes. As
> the attached screenshots show, the value turns negative every 30 minutes
> after the startup of the node.
> We did not experience this behavior in 2.1.16.
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