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https://issues.apache.org/jira/browse/CASSANDRA-11752?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15312796#comment-15312796
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Per Otterström commented on CASSANDRA-11752:
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By using sliding window only, all collected metrics from the last 5 minutes
will be equally significant.
On the other hand, by using decay only, the user may very well see values on
the percentiles even thought the node has not processed any requests for the
last five minutes.
The reason for having both a sliding window and decay would be to make the
metrics from the last minute more significant than the metrics collected 5
minutes ago. And an idling node would show zero-values on the percentiles after
5 minutes. But I may be over engineering this a bit. A pure decay approach is
probably good enough.
> histograms/metrics in 2.2 do not appear recency biased
> ------------------------------------------------------
>
> Key: CASSANDRA-11752
> URL: https://issues.apache.org/jira/browse/CASSANDRA-11752
> Project: Cassandra
> Issue Type: Bug
> Components: Core
> Reporter: Chris Burroughs
> Labels: metrics
> Attachments: boost-metrics.png, c-jconsole-comparison.png,
> c-metrics.png, default-histogram.png
>
>
> In addition to upgrading to metrics3, CASSANDRA-5657 switched to using a
> custom histogram implementation. After upgrading to Cassandra 2.2
> histograms/timer metrics are not suspiciously flat. To be useful for
> graphing and alerting metrics need to be biased towards recent events.
> I have attached images that I think illustrate this.
> * The first two are a comparison between latency observed by a C* 2.2 (us)
> cluster shoring very flat lines and a client (using metrics 2.2.0, ms)
> showing server performance problems. We can't rule out with total certainty
> that something else isn't the cause (that's why we measure from both the
> client & server) but they very rarely disagree.
> * The 3rd image compares jconsole viewing of metrics on a 2.2 and 2.1
> cluster over several minutes. Not a single digit changed on the 2.2 cluster.
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