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https://issues.apache.org/jira/browse/CASSANDRA-8413?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14614284#comment-14614284
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Robert Stupp commented on CASSANDRA-8413:
-----------------------------------------
Thanks.
Committed as 23fd75f27c40462636f09920719b5dcbef5b8f36 with a few sentences in
NEWS.txt regarding the new SSTable file version.
> Bloom filter false positive ratio is not honoured
> -------------------------------------------------
>
> Key: CASSANDRA-8413
> URL: https://issues.apache.org/jira/browse/CASSANDRA-8413
> Project: Cassandra
> Issue Type: Bug
> Components: Core
> Reporter: Benedict
> Assignee: Robert Stupp
> Fix For: 3.0 beta 1
>
> Attachments: 8413-patch.txt, 8413.hack-3.0.txt, 8413.hack.txt
>
>
> Whilst thinking about CASSANDRA-7438 and hash bits, I realised we have a
> problem with sabotaging our bloom filters when using the murmur3 partitioner.
> I have performed a very quick test to confirm this risk is real.
> Since a typical cluster uses the same murmur3 hash for partitioning as we do
> for bloom filter lookups, and we own a contiguous range, we can guarantee
> that the top X bits collide for all keys on the node. This translates into
> poor bloom filter distribution. I quickly hacked LongBloomFilterTest to
> simulate the problem, and the result in these tests is _up to_ a doubling of
> the actual false positive ratio. The actual change will depend on the key
> distribution, the number of keys, the false positive ratio, the number of
> nodes, the token distribution, etc. But seems to be a real problem for
> non-vnode clusters of at least ~128 nodes in size.
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