php - 这是使用内存缓存的最佳方式吗？

Question

我昨晚才开始玩 memcache(d)，所以我有很多东西要学

我想知道这段代码是否是完成它正在做的事情的好方法，或者我是否应该使用其他内存缓存函数

我想显示某物的缓存版本，如果缓存不存在，那么我从 mysql 生成内容并将其设置到缓存中，然后在页面上显示 mysql 结果，然后下一页加载它将检查缓存并查看它在那里，所以它会显示它。

这段代码似乎可以解决问题，但有几种不同的内存缓存函数，我应该使用其他函数来实现吗？

<?PHP
$memcache= new Memcache();
$memcache->connect('127.0.0.1', 11211);

$rows2= $memcache->get('therows1');
if($rows2 == ''){
    $myfriends = findfriend2(); // this function gets our array from mysql
    $memcache->set('therows1', $myfriends, 0, 30);
    echo '<pre>';
    print_r($myfriends); // print the mysql version
    echo '</pre>';
}else{
    echo '<pre>';
    print_r($rows2); //print the cached version
    echo '</pre>';
}
?>

这是@crescentfresh 发布的链接中提供的锁定功能

<?PHP
// {{{ locked_mecache_update($memcache,$key,$updateFunction,$expiryTime,$waitUTime,$maxTries)
/**
 * A function to do ensure only one thing can update a memcache at a time.
 *
 * Note that there are issues with the $expiryTime on memcache not being
 * fine enough, but this is the best I can do. The idea behind this form
 * of locking is that it takes advantage of the fact that
 * {@link memcache_add()}'s are atomic in nature.
 *
 * It would be possible to be a more interesting limiter (say that limits
 * updates to no more than 1/second) simply by storing a timestamp or
 * something of that nature with the lock key (currently stores "1") and
 * not deleitng the memcache entry.
 *
 * @package TGIFramework
 * @subpackage functions
 * @copyright 2009 terry chay
 * @author terry chay &lt;tychay@php.net&gt;
 * @param $memcache memcache the memcache object
 * @param $key string the key to do the update on
 * @param $updateFunction mixed the function to call that accepts the data
 *  from memcache and modifies it (use pass by reference).
 * @param $expiryTime integer time in seconds to allow the key to last before
 *  it will expire. This should only happen if the process dies during update.
 *  Choose a number big enough so that $updateFunction will take much less
 *  time to execute.
 * @param $waitUTime integer the amount of time in microseconds to wait before
 *  checking for the lock to release
 * @param $maxTries integer maximum number of attempts before it gives up
 *  on the locks. Note that if $maxTries is 0, then it will RickRoll forever
 *  (never give up). The default number ensures that it will wait for three
 *  full lock cycles to crash before it gives up also.
 * @return boolean success or failure
 */
function locked_memcache_update($memcache, $key, $updateFunction, $expiryTime=3, $waitUtime=101, $maxTries=100000)
{
    $lock = 'lock:'.$key;

    // get the lock {{{
    if ($maxTries>0) {
        for ($tries=0; $tries< $maxTries; ++$tries) {
            if ($memcache->add($lock,1,0,$expiryTime)) { break; }
            usleep($waitUtime);
        }
        if ($tries == $maxTries) {
            // handle failure case (use exceptions and try-catch if you need to be nice)
            trigger_error(sprintf('Lock failed for key: %s',$key), E_USER_NOTICE);
            return false;
        }
    } else {
        while (!$memcache->add($lock,1,0,$expiryTime)) {
            usleep($waitUtime);
        }
    }
    // }}}
    // modify data in cache {{{
    $data = $memcache->get($key, $flag);
    call_user_func($updateFunction, $data); // update data
    $memcache->set($key, $data, $flag);
    // }}}
    // clear the lock
    $memcache->delete($lock,0);
    return true;
}
// }}}
?>

Answer 1

一些事情。

1. 您应该在 return value from get() 中使用 === 检查 false，而不是 '' . php 的类型转换使您无需在此处执行此操作，但恕我直言，最好明确说明您从缓存查找中查找的值

2. 在空检查和 set() 数据库结果之间存在竞争条件。来自 http://code.google.com/p/memcached/wiki/FAQ#Race_conditions_and_stale_data :

   Remember that the process of checking memcached, fetching SQL, and storing into memcached, is not atomic at all!

   这种情况的症状是当 key 过期时数据库 CPU 出现峰值，并且(在高容量站点上)一堆请求同时尝试访问数据库并缓存值。

   您可以使用 add() 解决它而不是 get。查看更具体的示例 here .