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From "Jeff Jirsa (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-12922) Bloom filter miss counts are not measured correctly
Date Thu, 30 Nov 2017 21:34:00 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-12922?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16273498#comment-16273498
] 

Jeff Jirsa commented on CASSANDRA-12922:
----------------------------------------

[~krishnasun] are you still interested in writing the unit test?


> 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: Local Write-Read Paths
>            Reporter: Branimir Lambov
>            Assignee: Sundar Srinivasan
>              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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