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From Per Otterström (JIRA) <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-12876) Negative mean write latency
Date Tue, 08 Nov 2016 07:36:58 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-12876?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15646791#comment-15646791
] 

Per Otterström commented on CASSANDRA-12876:
--------------------------------------------

Yes, must be related to the 30 minute rescaling. I'm able o reproduce in a test cluster. I'm
seeing a similar pattern for the standard deviation as well.

Can't make out why this happens just by reviewing code, but I'll run some more tests.

> 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
>         Attachments: negative_mean.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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