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From "Stu Hood (JIRA)" <>
Subject [jira] Commented: (CASSANDRA-1555) Considerations for larger bloom filters
Date Mon, 06 Dec 2010 01:14:12 GMT


Stu Hood commented on CASSANDRA-1555:

* If BloomFilter is likely to be deprecated in favor of BigBloomFilter, naming them LegacyBloomFilter
and BloomFilter might reduce the surface area of future changes
* Probably a good opportunity to improve the serialization of BigBloomFilter: Java serialization
is very wasteful for space (each row would contain the string "org.apache.cassandra.utils.obs.OpenBitSet").
Instead, just serializing an OpenBitSet as a {{long[]}} and # of valid bits would be much
* (Big)BloomFilter
  * maxBucketsPerElement can be pushed up into Filter
  * getFilter could probably be pushed up to filter, or at least removed from BloomFilter
  * emptyBuckets is unused
* Orphaned method BigBloomFilter.serializeBitSet
* Indentation is off in SSTableReader and BigBloomFilter

I'm working on a separate issue to refresh LegacySSTableTest to check the column-level bloom
filters as well: see CASSANDRA-1822

> Considerations for larger bloom filters
> ---------------------------------------
>                 Key: CASSANDRA-1555
>                 URL:
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Stu Hood
>            Assignee: Ryan King
>             Fix For: 0.8
>         Attachments: cassandra-1555.tgz, CASSANDRA-1555v2.patch
> To (optimally) support SSTables larger than 143 million keys, we need to support bloom
filters larger than 2^31 bits, which java.util.BitSet can't handle directly.
> A few options:
> * Switch to a BitSet class which supports 2^31 * 64 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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