[Tickets #13085] Re: Use memcache instead of distributed hashtable in $conf[cache][driver]

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Ticket URL: http://bugs.horde.org/ticket/13085
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  Ticket             | 13085
  Updated By         | Michael Slusarz <slusarz at horde.org>
  Summary            | Use memcache instead of distributed hashtable in
                     | $conf[cache][driver]
  Queue              | Horde Framework Packages
  Version            | Git master
  Type               | Bug
  State              | Feedback
  Priority           | 1. Low
  Milestone          |
  Patch              |
  Owners             | Michael Slusarz
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Michael Slusarz <slusarz at horde.org> (2014-03-31 23:45) wrote:

> But in that case it is still a waste of cache, to keep entries  
> around for the configured default value for the cache lifetime,  
> while we already know it will not be used anymore after $lifetime  
> seconds in the future.

Not for memcache.  Again, you don't need to worry about expiration for  
memcache since old entries will automatically be pruned.  Dealing with  
GC is just adding unnecessary overhead.

And for many purposes, it is advantageous to use the cache if it  
exists, regardless of lifetime.  You might want to limit the size of  
your file-based cache by providing a max lifetime ... not because the  
data has an expiration date but simply because you want to limit the  
number of entries.  But the brilliance of memcache is that it makes  
this part of the calculus obsolete: the data is available until you  
run out of space.

> We already know that at the time of setting the cache value, so it  
> seems a waste not to use that knowledge.

Except, theoretically, you could set a cache value and then try to  
grab it later in two different locations ... and one of those  
locations may have a different (or no) lifetime argument.  So it is  
not that simple.

All this being said... I believe the issue here is simply that the  
Horde_Hashtable driver doesn't currently honor the $lifetime parameter  
in get():

     /**
      * NOTE: This driver ignores the lifetime argument.
      */
     public function get($key, $lifetime = 0)
     {
         return $this->_hash->get($this->_params['prefix'] . $key);
     }

Looks like that needs to be written (exists() also).