Classic and block-style bloom filters.

bloomfilter-blocked

bloomfilter-blocked is a Haskell library providing multiple fast and efficient implementations of bloom filters. It is a full rewrite of the bloomfilter package, originally authored by Bryan O'Sullivan [email protected].

A bloom filter is a space-efficient data structure representing a set that can be probablistically queried for set membership. The set membership query returns no false negatives, but it might return false positives. That is, if an element was added to a bloom filter, then a subsequent query definitely returns True. If an element was not added to a filter, then a subsequent query may still return True if False would be the correct answer. The probabiliy of false positives -- the false positive rate (FPR) -- is configurable.

The library includes two implementations of bloom filters: classic, and blocked.

• Classic bloom filters, found in the Data.BloomFilter.Classic module: a default implementation that is faithful to the canonical description of a bloom filter data structure.

• Blocked floom filters, found in the Data.BloomFilter.Blocked module: an implementation that optimises the memory layout of a classic bloom filter for speed (cheaper CPU cache reads), at the cost of a slightly higher FPR for the same amount of assigned memory.

The FPR scales inversely with how much memory is assigned to the filter. It also scales inversely with how many elements are added to the set. The user can configure how much memory is asisgned to a filter, and the user also controls how many elements are added to a set. Each implementation comes with helper functions, like sizeForFPR and sizeForBits, that the user can leverage to configure filters.

Both immutable (Bloom) and mutable (MBloom) bloom filters, including functions to convert between the two, are provided for each implementation. Note however that a (mutable) bloom filter can not be resized once created, and that elements can not be deleted once inserted.

For more information about the library and examples of how to use it, see the Haddock documentation of the different modules.

Usage notes

User should take into account the following:

• This package is not supported on 32bit systems.

Differences from the bloomfilter package

The library is a full rewrite of the bloomfilter package, originally authored by Bryan O'Sullivan [email protected]. The main differences are:

• bloomfilter-blocked supports both classic and blocked bloom filters, whereas bloomfilter only supports the former.
• bloomfilter-blocked supports bloom filters of arbitrary sizes, whereas bloomfilter limits the sizes to powers of two.
• bloomfilter-blocked supports sizes up to 2^48 for classic bloom filters and up to 2^41 for blocked bloom filters, instead of 2^32.
• In bloomfilter-blocked, the Bloom and MBloom types are parameterised over a Hashable type class, instead of having a a -> [Hash] typed field. This separation in bloomfilter-blocked allows clean (de-)serialisation of filters as the hashing scheme is static.
• bloomfilter-blocked uses XXH3 for hashing instead of Jenkins' lookup3, which bloomfilter uses.
• The user can configure hash salts for improved security in bloomfilter-blocked, whereas this is not supported in bloomfilter.