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https://issues.apache.org/jira/browse/CASSANDRA-10585?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15010712#comment-15010712
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Ivan Burmistrov commented on CASSANDRA-10585:
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I think, extending EstimatedHistogram to properly capture a 0 value is more
preferably. Because not only row cache may cause reading 0 SSTables, but
[CASSANDRA-2498|https://issues.apache.org/jira/browse/CASSANDRA-2498] and
[CASSANDRA-5514|https://issues.apache.org/jira/browse/CASSANDRA-5514]
optimizations too: read request can process only Memtable without touching any
SSTable if these optimizations work well.
I will prepare new versions of patches and will attach it for your review soon.
> 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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