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From "Sylvain Lebresne (JIRA)" <>
Subject [jira] Commented: (CASSANDRA-1555) Considerations for larger bloom filters
Date Wed, 29 Sep 2010 16:02:34 GMT


Sylvain Lebresne commented on CASSANDRA-1555:

Even if we should probably have a way to support big BF, it would still be nice to be able
configure the BF FP rate. 2+GB for BFs can start to be an heavy weight on your memory. 
For some loads, it could be better to actually keep your memory for row cache for instance.

> Considerations for larger bloom filters
> ---------------------------------------
>                 Key: CASSANDRA-1555
>                 URL:
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Stu Hood
>             Fix For: 0.8
> To (optimally) support SSTables larger than 143 million keys, we need to support bloom
filters larger than 2 GB, which java.util.BitSet can't handle directly.
> A few options:
> * Switch to a BitSet class which supports 2^63 bits (Lucene's OpenBitSet)
> * Partition the java.util.BitSet behind our current BloomFilter
> ** Straightforward bit partitioning: bit N is in bitset N // 2^31
> ** Separate equally sized complete bloom filters for member ranges, which can be used
independently or OR'd together under memory pressure.
> All of these options require new approaches to serialization.

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