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https://issues.apache.org/jira/browse/CASSANDRA-7731?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14095171#comment-14095171
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Cyril Scetbon edited comment on CASSANDRA-7731 at 8/13/14 6:49 AM:
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[~snazy] in the first part, you're totally right about the use of exponentially
decaying reservoirs. I didn't see that at first. Cool. Yeah, you could use a
better name for variables but as long as it does what it should that's fine for
me :) The message is clear in CFSTAT about this. Renaming them to be clearer
could help developers too.
For the second part, that's a yes. I think we really need to know the last max
for live and tombstone cells number of reads. We hit 2 development bugs related
to this and monitoring that could really help ! So using 2 more histograms
(with biased=true) for those max values should help and is a must have.
Can you also confirm that calling CFSTAT does not reset internal counters at
the end of the call ? I understand that for the histograms above it doesn't,
but what about the others ?
was (Author: cscetbon):
[~snazy] in the first part, you're totally right about the use of exponentially
decaying reservoirs. I didn't see that at first. Cool. Yeah, you could use a
better name for variables but as long as it does what it should that's fine for
me :) The message is clear in CFSTAT about this. Renaming them to be clearer
could help developers too.
For the second part, that's a yes. I think we really need to know the last max
for live and tombstone cells number of reads. We hit 2 development bugs related
to this and monitoring that could really help ! So using 2 more histograms
(with biased=true) for those max values should help and is a must have.
Can you just confirm that calling CFSTAT does not reset internal counters at
the end of the call ? I understand that for the histograms above it doesn't,
but what about the others ?
> Average 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
>
> 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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