NAME

Bloom::Faster - Perl extension for the c library libbloom.

INSTALLATION

see INSTALL

SYNOPSIS

  use Bloom::Faster;
  
  # m = ideal vector size.  
  # k = # of hash functions to use. 

  my $bloom = new Bloom::Faster({m => 1000000,k => 5});

  # this gives us very tight control of memory usage (a function of m)
  # and performance (a function of k).  but in most applications, we won't
  # know the optimal values of either of these.  for these cases, it is 
  # much easier to supply:
  #
  # n = number of expected elements to check for duplicates,
  # e = acceptable error rate (probability of false positive)
  #
  # my $bloom = new Bloom::Faster({n => 1000000, e => 0.00001});

  while (<>) {
        chomp;
        # Bloom::Faster->add() returns true when the value is a duplicate.
        if ($bloom->add($_)) {
                print "DUP: $_\n";
        }
  }

DESCRIPTION

Bloom filters are a lightweight duplicate detection algorithm proposed by Burton Bloom (http://portal.acm.org/citation.cfm?id=362692&dl=ACM&coll=portal), with applications in stream data processing, among otheres. Bloom filters are a very cool thing. Where occasional false positives are acceptable, bloom filters give us the ability to detect duplicates in a fast and resource-friendly manner.

The allocation of memory for the bit vector is handled in the c layer, but perl's oo capability handles the garbage collection. when a Bloom::Faster object goes out of scope, the vector pointed to by the c structure will be free()d. to manually do this, the DESTROY builtin method can be called.

A bloom filter perl module is currently avaible on CPAN, but it is profoundly slow and cannot handle large vectors. This alternative uses a more efficient c library which can handle arbitrarily large vectors (up to the maximum size of a "long long" datatype (at least 9223372036854775807).

EXPORT

None by default.

Exportable constants

  HASHCNT
  PRIME_SIZ
  SIZ

SEE ALSO

libbbloom.so

AUTHOR

Peter Alvaro and Dmitriy Ryaboy, <palvaro@ask.com>

COPYRIGHT AND LICENSE

Copyright (C) 2006 by Peter Alvaro and Dmitriy Ryaboy

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.8.5 or, at your option, any later version of Perl 5 you may have available.