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From "Cyril Scetbon (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (CASSANDRA-7731) Get max values for live/tombstone cells per slice
Date Mon, 15 Sep 2014 16:35:34 GMT

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Cyril Scetbon edited comment on CASSANDRA-7731 at 9/15/14 4:34 PM:
-------------------------------------------------------------------

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]
and you said that non percentile functions return values since the application started. 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



was (Author: cscetbon):
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 !



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