这是使用memcache的最佳方式吗？

Question

我昨晚刚刚开始玩memcache(d),所以我有很多东西需要了解它

我想知道这段代码是否是一种很好的方式来做它正在做的事情或者我是否应该使用其他memcache函数

我想显示一些缓存版本的东西,如果缓存不存在那么我从mysql生成内容并将其设置为缓存然后在页面上显示mysql结果,然后下一页加载它将检查缓存并看到它是那里,所以它会显示出来.

这段代码似乎可以解决这个问题但是我应该使用其他几种不同的memcache函数来实现这一目的吗？

<?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

几件事.

1. 你应该检查false,不''使用===在从返回值get().php的类型转换可以避免你在这里做到这一点,但是恕我直言,最好明确你要从缓存查找中寻找的值

2. 你在空检查和set()数据库结果之间有一个竞争条件.来自http://code.google.com/p/memcached/wiki/FAQ#Race_conditions_and_stale_data:

   请记住,检查memcached,获取SQL以及存储到memcached中的过程根本不是原子的!

   这种情况的症状是密钥到期时DB CPU中的峰值,并且(在高容量站点上)一堆请求同时尝试命中数据库并缓存该值.

   您可以使用add()而不是使用来解决它get.在这里查看更具体的示例.