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https://issues.apache.org/jira/browse/CASSANDRA-12876?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15658190#comment-15658190
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Kévin LOVATO commented on CASSANDRA-12876:
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I updated a node of a test cluster with your patch and it works, no more
negative values, thanks :)
The code in the patch was clear, but I'm a bit confused regarding your
explanation. You mention that the overflow happens because of the addition of
all the buckets during the mean computation, only to be fixed by the rescaling
(that happens every 30 minutes). But then why do I only observe negative values
every 30 minutes ? Shouldn't I observe negative values all the time, and
positive ones just after the rescale ?
> 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
> Fix For: 2.2.9
>
> Attachments: 12876-2.2.txt, 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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