[jira] [Updated] (CASSANDRA-12922) Bloom filter miss counts are not measured correctly

["Jeremy Hanna (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CASSANDRA-12922?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Jeremy Hanna updated CASSANDRA-12922:
-------------------------------------
    Complexity: Low Hanging Fruit

> Bloom filter miss counts are not measured correctly
> ---------------------------------------------------
>
>                 Key: CASSANDRA-12922
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-12922
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Legacy/Local Write-Read Paths
>            Reporter: Branimir Lambov
>            Assignee: Sundar Srinivasan
>            Priority: Normal
>              Labels: lhf
>             Fix For: 4.x
>
>         Attachments: 12922-trunk.txt
>
>
> Bloom filter hits and misses are evaluated incorrectly in {{BigTableReader.getPosition}}: we properly record hits, but not misses. In particular, if we don't find a match for a key in the index, which is where almost all non-matches will be rejected, [we don't record a bloom filter false positive|https://github.com/apache/cassandra/blob/trunk/src/java/org/apache/cassandra/io/sstable/format/big/BigTableReader.java#L228].
> This leads to very misleading output from e.g. {{nodetool tablestats}}.



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