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https://issues.apache.org/jira/browse/CASSANDRA-10585?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15003635#comment-15003635
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Ivan Burmistrov commented on CASSANDRA-10585:
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I have prepared patches to versions 2.1, 2.2 and 3.0 (and it is not hard to
prepare patch for trunk).
Important comment for 2.2 and 3.0 versions.
SSTablePerReadHistogram in these versions is EstimatedHistogram now.
But for this implementation of histogram zero values make almost no effect.
It seems not good, because it is important to know if, for example, we read 0.1
SSTables per read at average.
For example, we want to know do
https://issues.apache.org/jira/browse/CASSANDRA-2498 and
https://issues.apache.org/jira/browse/CASSANDRA-5514 optimizations works for
some table.
EstimatedHistogram returns only integer values and make this scenario
impossible, while it was possible in versions 2.1 and below.
So in patches for 2.2 and 3.0 I switched SSTablesPerReadHistogram to
ExponentiallyDecayingHistogram implementation.
> SSTablesPerReadHistogram seems wrong when row cache hit happend
> ---------------------------------------------------------------
>
> Key: CASSANDRA-10585
> URL: https://issues.apache.org/jira/browse/CASSANDRA-10585
> Project: Cassandra
> Issue Type: Bug
> Reporter: Ivan Burmistrov
> Priority: Minor
> Fix For: 2.1.x, 2.2.x, 3.0.x
>
> Attachments: SSTablePerReadHistogram_RowCache-cassandra-2_1.patch,
> SSTablePerReadHistogram_RowCache-cassandra-2_2.patch,
> SSTablePerReadHistogram_RowCache-cassandra-3_0.patch
>
>
> SSTablePerReadHistogram metric now not considers case when row has been read
> from row cache.
> And so, this metric will have big values even almost all requests processed
> by row cache (and without touching SSTables, of course).
> So, it seems that correct behavior is to consider that if we read row from
> row cache then we read zero SSTables by this request.
> The patch at the attachment.
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