/core/Cache/AggregateCache.class.php

<?php
/****************************************************************************
 *   Copyright (C) 2005-2008 by Anton E. Lebedevich, Konstantin V. Arkhipov *
 *                                                                          *
 *   This program is free software; you can redistribute it and/or modify   *
 *   it under the terms of the GNU Lesser General Public License as         *
 *   published by the Free Software Foundation; either version 3 of the     *
 *   License, or (at your option) any later version.                        *
 *                                                                          *
 ****************************************************************************/

	/**
	 * A wrapper to multiple cache for workload
	 * distribution using CachePeer childs.
	 * 
	 * @ingroup Cache
	**/
	class AggregateCache extends BaseAggregateCache
	{
		const LEVEL_ULTRAHIGH	= 0xFFFF;
		const LEVEL_HIGH		= 0xC000;
		const LEVEL_NORMAL		= 0x8000;
		const LEVEL_LOW			= 0x4000;
		const LEVEL_VERYLOW		= 0x0001;
		
		private $levels		= array();

		/**
		 * @return AggregateCache
		**/
		public static function create()
		{
			return new self;
		}

		/**
		 * @return AggregateCache
		**/
		public function addPeer(
			$label, CachePeer $peer, $level = self::LEVEL_NORMAL
		)
		{
			$this->doAddPeer($label, $peer);

			$this->peers[$label]['level'] = $level;
			
			return $this;
		}
		
		/**
		 * @return AggregateCache
		**/
		public function setClassLevel($class, $level)
		{
			$this->levels[$class] = $level;
			
			return $this;
		}
		
		/**
		 * brain
		**/
		protected function guessLabel($key)
		{
			$class = $this->getClassName();

			if (isset($this->levels[$class]))
				$classLevel = $this->levels[$class];
			else
				$classLevel = self::LEVEL_NORMAL;
			
			// init by $key, randomness will be restored later
			mt_srand(hexdec(substr(md5($key), 3, 7)));

			$zeroDistances = array();
			$weights = array();

			foreach ($this->peers as $label => $peer) {
				$distance = abs($classLevel - $peer['level']);

				if (!$distance)
					$zeroDistances[] = $label;
				else
					$weights[$peer['level']] = 1 / pow($distance, 2); // BOVM
			}
			
			if (count($zeroDistances)) {

				$selectedLabel =
					$zeroDistances[mt_rand(0, count($zeroDistances) - 1)];

			} else {

				// weighted random level selection
				$sum = mt_rand() * array_sum($weights) / mt_getrandmax();
				$peerLevel = null;
				foreach ($weights as $level => $weight) {
					if ($sum <= $weight) {
						$peerLevel = $level;
						break;
					} else
						$sum -= $weight;
				}

				$selectedPeers = array();
				foreach ($this->peers as $label => $peer) {
					if ($peer['level'] == $peerLevel)
						$selectedPeers[] = $label;
				}

				$selectedLabel = $selectedPeers[mt_rand(0, count($selectedPeers) - 1)];
			}

			if (isset($this->peers[$selectedLabel]['stat'][$class]))
				++$this->peers[$selectedLabel]['stat'][$class];
			else
				$this->peers[$selectedLabel]['stat'][$class] = 1;
			
			// restore randomness
			mt_srand(
				(int) (
					(int) (microtime(true) << 2)
					* (rand(time() / 2, time()) >> 2)
				)
			);
			
			return $selectedLabel;
		}
	}
?>