這是使用memcache的最佳方式嗎？

Question

我剛開始用的memcache玩（d）昨晚，所以我還有很多要學習一下吧

我想知道如果這個代碼是在做它在做什麼，或者我應該使用的好辦法其他memcache功能

我想顯示緩存版本的東西，如果緩存不存在，那麼我從mysql生成內容並將其設置爲緩存，然後在頁面上顯示mysql結果，然後下一頁加載它會檢查緩存，看看它在那裏，所以它會顯示它。

這段代碼似乎有訣竅，但有幾種不同的memcache函數應該使用其他的來實現這個功能嗎？

<?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>'; 
} 
?> 

這裏是發佈的鏈接提供的鎖定功能通過@crescentfresh

<?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

夫婦的事情。

1. 你應該在return value from get()使用===進行檢查false，不''。 PHP的類型轉換可以幫助您避免這樣做，但是恕我直言，最好是從緩存查找中明確您正在查找的值

2. 您的競爭條件存在於空白檢查和您在哪裏set() db結果。從http://code.google.com/p/memcached/wiki/FAQ#Race_conditions_and_stale_data：

   記住檢查 的memcached，獲取SQL和存儲 到的memcached的過程中，是不是原子的了！

   這種情況的症狀是，當密鑰過期並且（在一個高容量的站點上）一堆請求同時嘗試擊中db並緩存該值時，數據庫CPU中會出現尖峯。

   您可以使用add()而不是get來解決。看一個更具體的例子here。