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https://issues.apache.org/jira/browse/CASSANDRA-11752?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15312659#comment-15312659
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Chris Lohfink commented on CASSANDRA-11752:
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I am confused on why you have a sliding window and decaying function. can kinda
just do one or the other.
Sliding Window: if keeping 5 copies of the EH why not just have the same as EH
but keep a buffer of long[5][offsetsize] that every minute takes the current
values of the bucket and stores them. then on read compare oldest in the buffer
to the current, and the delta is the last 5 minutes. can treat the long[5] as a
cyclic buffer. Can still provide the current "getValues" as the current total
value but the percentiles can be computed on the delta.
Decayed: I was thinking more like a
http://www.source-code.biz/snippets/java/11.htm per bucket (a forward decaying
i think would be best). Why keep the 5 sets of them?
Decaying the snapshots sounds like it has the overhead of a sliding window and
the complexity/performance/accuracy impact of a decaying algorithm. although I
might have to see the implementation and may be missing something though.
> 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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