Flexihash

Flexihash is a small PHP library which implements [http://en.wikipedia.org/wiki/Consistent_hashing consistent hashing], which is most useful in distributed caching. It requires PHP5 and uses [http://simpletest.org/ SimpleTest] for unit testing.

Usage Example

<?php

$hash = new Flexihash();

if ($data = $cache->get('myhash'))
{
    $hash = unserialize($data);
}
else
{
    // bulk add
    $hash->addTargets(array('cache-1', 'cache-2', 'cache-3'));

    // save costly initialized hash for later use
    $cache->set('myhash', serialize($hash));
}

// simple lookup
$hash->lookup('object-a'); // "cache-1"
$hash->lookup('object-b'); // "cache-2"

// add and remove
$hash
  ->addTarget('cache-4')
  ->removeTarget('cache-1');

// lookup with next-best fallback (for redundant writes)
$hash->lookupList('object', 2); // ["cache-2", "cache-4"]

// remove cache-2, expect object to hash to cache-4
$hash->removeTarget('cache-2');
$hash->lookup('object'); // "cache-4"

Further Reading

• http://www.spiteful.com/2008/03/17/programmers-toolbox-part-3-consistent-hashing/
• http://weblogs.java.net/blog/tomwhite/archive/2007/11/consistent_hash.html