Luben Karavelov > Hash-ConsistentHash > Hash::ConsistentHash

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NAME ^

Hash::ConsistentHash - Constant hash algorithm

VERSION ^

Version 0.05

SYNOPSIS ^

    use Hash::ConsistentHash;
    use String::CRC32;

    my $chash = Hash::ConsistentHash->new(
        buckets   => [qw(10.0.0.1 10.0.0.2 10.0.0.3 10.0.0.4)],
        hash_func => \&crc32
    );
    # get just one bucket
    my $server = $chash->get_bucket('foo');

    # or get a serie of non-repeating buckets through iterator
    my $next  = $chash->lookup('bar');
    $server   = $next->(); # get bucket
    # do stuff with $server
    $server   = $next->(); # get another bucket
    ...

DESCRIPTION ^

Hash::ConsistentHash algorithm distributes keys over fixed number of buckets. Constant hash distribution means that if we add a bucket to a hash with N buckets filled with M keys we have to reassign only M/(N+1) keys to new buckets.

What puts apart this module from all similar modules available is that you could ask for non-repeatable series of buckets. Using this property you could implement not only consistent distribution but also redundancy - one key to be directed to more than one bucket.

METHODS ^

new

Creates ConsistentHash object. It accept following params:

hash_func

Hash function to be used on keys and buckets

buckets

Arrayref or Hashref. If buckets are given as arrayref they will have same weight. If given as hashref, every bucket could have differend weight.

Examples:

    # All buckets have same weight so they will hold equal amount of keys
    my $chash = Hash::ConsistentHash->new(
        buckets => [qw(A B C)],
        hash_func=>\&crc32 );

    # Bucket "B" will hold twice the amount of keys of bucket A or C
    my $chash = Cash::ConsistentHash->new(
        buckets => {A=>1, B=>2, C=>1},
        hash_func=>\&crc32 );

lookup

Lookup a key in the hash. Accept one param - the key. Returns an iterator over the hash buckets.

Example:

    my $chash = Hash::ConsistentHash->new(
        buckets => [qw(A B C)],
        hash_func=>\&crc32 );

    my $next   = $chash->lookup('foo');
    my $bucket = $next->(); # B
    $bucket    = $next->(); # A
    $bucket    = $next->(); # C, hash is exhausted
    $bucket    = $next->(); # A
    ...

Returned buckets will not repeat until all buckets are exhausted.

get_bucket

Lookup a key in the hash. Accept one param - the key. Returns a bucket.

Example:

    my $chash = Hash::ConsistentHash->new(
        buckets => [qw(A B C)],
        hash_func=>\&crc32 );

    my $bucket  = $chash->get_bucket('foo');

SEE ALSO ^

Set::ConsistentHash, Algorithm::ConsistentHash::Ketama

AUTHOR ^

Luben Karavelov, <karavelov at spnet.net>

BUGS ^

Please report any bugs or feature requests to bug-hash-consistenthash at rt.cpan.org, or through the web interface at http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Hash-ConsistentHash. I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.

SUPPORT ^

You can find documentation for this module with the perldoc command.

    perldoc Hash::ConsistentHash

You can also look for information at:

LICENSE AND COPYRIGHT ^

Copyright 2011 Luben Karavelov.

This program is free software; you can redistribute it and/or modify it under the terms of either: the GNU General Public License as published by the Free Software Foundation; or the Artistic License.

See http://dev.perl.org/licenses/ for more information.

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