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Additional in-process cache plugin InProcessCache

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Some of our caching systems, like the disk cache or memcached, have
significant overhead (network connections or disk I/O).

This plugin adds an additional layer of in-process cache, so we don't
need to reconnect to external cache systems when we've already
received a data item from the cache. There are some concurrency issues
here, but typically they won't be important at the level of a single
web hit.
This commit is contained in:
Evan Prodromou 2010-12-09 10:45:36 -05:00
parent 94ff04e190
commit f5f6a742cb
1 changed files with 197 additions and 0 deletions
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197
plugins/InProcessCache/InProcessCachePlugin.php Normal file
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<?php
/**
* StatusNet - the distributed open-source microblogging tool
* Copyright (C) 2010, StatusNet, Inc.
*
* Extra level of caching, in memory
*
* PHP version 5
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* @category Cache
* @package StatusNet
* @author Evan Prodromou <evan@status.net>
* @copyright 2010 StatusNet, Inc.
* @license http://www.fsf.org/licensing/licenses/agpl-3.0.html AGPL 3.0
* @link http://status.net/
*/
if (!defined('STATUSNET')) {
// This check helps protect against security problems;
// your code file can't be executed directly from the web.
exit(1);
}
/**
* Extra level of caching
*
* This plugin adds an extra level of in-process caching to any regular
* cache system like APC, XCache, or Memcache.
*
* Note that since most caching plugins return false for StartCache*
* methods, you should add this plugin before them, i.e.
*
* addPlugin('InProcessCache');
* addPlugin('XCache');
*
* @category Cache
* @package StatusNet
* @author Evan Prodromou <evan@status.net>
* @copyright 2010 StatusNet, Inc.
* @license http://www.fsf.org/licensing/licenses/agpl-3.0.html AGPL 3.0
* @link http://status.net/
*/
class InProcessCachePlugin extends Plugin
{
private $_items = array();
private $_hits = array();
/**
* Get an item from the cache
*
* Called before other cache systems are called (iif this
* plugin was loaded correctly, see class comment). If we
* have the data, return it, and don't hit the other cache
* systems.
*
* @param string &$key Key to fetch
* @param mixed &$value Resulting value or false for miss
*
* @return boolean false if found, else true
*/
function onStartCacheGet(&$key, &$value)
{
if (array_key_exists($key, $this->_items)) {
$value = $this->_items[$key];
if (array_key_exists($key, $this->_hits)) {
$this->_hits[$key]++;
} else {
$this->_hits[$key] = 1;
}
Event::handle('EndCacheGet', array($key, &$value));
return false;
}
return true;
}
/**
* Called at the end of a cache get
*
* If we don't already have the data, we cache it. This
* keeps us from having to call the external cache if the
* key is requested again.
*
* @param string $key Key to fetch
* @param mixed &$value Resulting value or false for miss
*
* @return boolean hook value, true
*/
function onEndCacheGet($key, &$value)
{
if (!array_key_exists($key, $this->_items) ||
$this->_items[$key] != $value) {
$this->_items[$key] = $value;
}
return true;
}
/**
* Called at the end of setting a cache element
*
* Always set the cache element; may overwrite existing
* data.
*
* @param string $key Key to fetch
* @param mixed $value Resulting value or false for miss
* @param integer $flag ignored
* @param integer $expiry ignored
*
* @return boolean true
*/
function onEndCacheSet($key, $value, $flag, $expiry)
{
$this->_items[$key] = $value;
return true;
}
/**
* Called at the end of deleting a cache element
*
* If stuff's deleted from the other cache, we
* delete it too.
*
* @param string &$key Key to delete
* @param boolean &$success Success flag; ignored
*
* @return boolean true
*/
function onStartCacheDelete(&$key, &$success)
{
if (array_key_exists($key, $this->_items)) {
unset($this->_items[$key]);
}
return true;
}
/**
* Version info
*
* @param array &$versions Array of version blocks
*
* @return boolean true
*/
function onPluginVersion(&$versions)
{
$url = 'http://status.net/wiki/Plugin:InProcessCache';
$versions[] = array('name' => 'InProcessCache',
'version' => STATUSNET_VERSION,
'author' => 'Evan Prodromou',
'homepage' => $url,
'description' =>
_m('Additional in-process cache for plugins.'));
return true;
}
/**
* Cleanup function; called at end of process
*
* If the inprocess/stats config value is true, we dump
* stats to the log file
*
* @return boolean true
*/
function cleanup()
{
if (common_config('inprocess', 'stats')) {
$this->log(LOG_INFO, "cache size: " .
count($this->_items));
$sum = 0;
foreach ($this->_hits as $hitcount) {
$sum += $hitcount;
}
$this->log(LOG_INFO, $sum . " hits on " .
count($this->_hits) . " keys");
}
return true;
}
}