Memcached没有听到过期时间(Memcached not listening to expiration time)

 我正在将Memcached与我在CodeIgniter中编写的PHP Web应用程序结合使用。 我利用这个Memcached库https://github.com/tomschlick/memcached-library当我缓存数据时，我给它一个7200或2小时的到期时间。 
 
 模型查询的片段： 
 
$result = $this->memcached_library->get(md5($sql));
if (!$result) {
     $cursor = $this->db->query($sql);
     $result = $cursor->row();
     $this->memcached_library->set(md5($sql), $result, 7200);
}
return $result;
 
 很酷，这适用于将数据设置为Memcached。 我可以看到结果，一切都运作良好。 问题出现在将此数据放入Memcached后2小时后。 
 
 根据我的理解，当执行get函数时，Memcached应​​该认识到缓存的数据已经超过其过期日期，因此将其标记为无效（但不一定将其从内存中删除）。 当PHP调用获取数据时，它应返回false，这将导致我的if语句被评估为true并重新获取数据并再次在Memcached中设置数据。 
 
 但是，似乎Memcached从未说过数据无效，并且在2小时到期限制之前存在相同的旧数据。 如果我在Memcached上手动调用flush（使缓存中的所有数据无效），数据将再次正确设置为Memcached，但我们再次遇到相同的2小时到期限制问题。 

I'm using Memcached in conjunction with my PHP web app written in CodeIgniter. I utilize this Memcached library https://github.com/tomschlick/memcached-library When I cache data, I give it an expiration time of 7200, or 2 hours.
 
Snippet of a model query:
 
$result = $this->memcached_library->get(md5($sql));
if (!$result) {
     $cursor = $this->db->query($sql);
     $result = $cursor->row();
     $this->memcached_library->set(md5($sql), $result, 7200);
}
return $result;
 
Cool, this works for setting data into Memcached. I can see the results, all is working well. The problem comes in that after 2 hours after placing this data into Memcached.
 
From my understanding, when executing the get function, Memcached should recognize that the cached data has hit past its expired date and thus marks it as invalid (not necessarily deleting it from memory however). When the PHP call to get the data, it should return false, which will then in turn cause my if statement to be evaluated as true and refetch the data and set the data in Memcached yet again.
 
However, it seems as if Memcached never says the data is invalid, and the same old data is in there from before the 2 hour expiration limit. If I manually call flush on Memcached (invalidating all data in the cache), the data is set into Memcached properly yet again, but we run into the same 2 hour expiration limit problem yet again.

原文：https://stackoverflow.com/questions/14225755