[jira] [Created] (CASSANDRA-7731) Average live/tombstone cells per slice

["Cyril Scetbon (JIRA)" <ji...@apache.org>]

Cyril Scetbon created CASSANDRA-7731:
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             Summary: 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
            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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