[
https://issues.apache.org/jira/browse/CASSANDRA-11752?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15448327#comment-15448327
]
Per Otterström commented on CASSANDRA-11752:
--------------------------------------------
Interesting comparison. And I'm a bit surprised by the results. I would expect
the EH to exaggerate peaks rather than the other way around as it registers
measurements in fixed value buckets rounding _upwards_.
I wonder if this could be an effect of the fact that the EDR is based on
samples. This means that sometimes it can miss an outlier, but could this also
mean that if an outlier is caught it can be over-represented in the histogram?
Another explanation could be that the decay is to quick or slow in the DEHR
(half-time set to one minute right now). How frequently do you take readings?
> 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
> Assignee: Per Otterström
> Labels: metrics
> Fix For: 2.2.8, 3.0.9, 3.8
>
> Attachments: 11752-2.2-v2.txt, 11752-2.2-v2b.txt, 11752-2.2.txt,
> boost-metrics.png, c-jconsole-comparison.png, c-metrics.png,
> default-histogram.png, server-patch-v2.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.
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
