[
https://issues.apache.org/jira/browse/CASSANDRA-7731?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14134088#comment-14134088
]
Cyril Scetbon commented on CASSANDRA-7731:
------------------------------------------
For the 2.1 patch I understand that it could not work as expected as it's not
using a percentile when it calls
[HistogramMBean.getMax|https://github.com/dropwizard/metrics/blob/v2.2.0/metrics-core/src/main/java/com/yammer/metrics/reporting/JmxReporter.java#L210-L212].
However, I'm using the [2.0
patch|https://issues.apache.org/jira/secure/attachment/12661546/7731-2.0.txt]
which internally uses metric.liveScannedHistogram.cf.getSnapshot().getValue(1d)
which gets the maximum from a percentile. However, as you saw in my logs, it
doesn't work better and returns an old maximum
> Get max values for live/tombstone cells per slice
> -------------------------------------------------
>
> Key: CASSANDRA-7731
> URL: https://issues.apache.org/jira/browse/CASSANDRA-7731
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Reporter: Cyril Scetbon
> Assignee: Robert Stupp
> Priority: Minor
> Fix For: 2.1.1
>
> Attachments: 7731-2.0.txt, 7731-2.1.txt
>
>
> I think you should not say that slice statistics are valid for the [last five
> minutes
> |https://github.com/apache/cassandra/blob/cassandra-2.0/src/java/org/apache/cassandra/tools/NodeCmd.java#L955-L956]
> in CFSTATS command of nodetool. I've read the documentation from yammer for
> Histograms and there is no way to force values to expire after x minutes
> except by
> [clearing|http://grepcode.com/file/repo1.maven.org/maven2/com.yammer.metrics/metrics-core/2.1.2/com/yammer/metrics/core/Histogram.java#96]
> it . The only thing I can see is that the last snapshot used to provide the
> median (or whatever you'd used instead) value is based on 1028 values.
> I think we should also be able to detect that some requests are accessing a
> lot of live/tombstone cells per query and that's not possible for now without
> activating DEBUG for SliceQueryFilter for example and by tweaking the
> threshold. Currently as nodetool cfstats returns the median if a low part of
> the queries are scanning a lot of live/tombstone cells we miss it !
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
