Question

Consider the following code:

function getUser($uid) {
    global $_memcache;
    $u = $_memcache->get("user-".$uid);
    if( !$u) {
        $u = ... // get user from database
        $_memcache->set("user-".$uid,$u);
    }
    return $u;
}

Now, this function will probably be called a LOT. For instance, on the forum it may be called 30+ times in a single pageload. Is it worth doing the following, or is Memcache already optimal enough?

function getUser2($uid) {
    static $localcache = [];
    if( isset($localcache[$uid])) return $localcache[$uid];
    return $localcache[$uid] = getUser($uid);
}

Answer 1

Well ultimately memcached is in memory storage, just as storing the values in PHP array would be. If the memcached instance is on the same server that you are running the code on, then I would definitely say just use memcached instead of both memcached and the PHP array, as you would end up just using ~ twice as much memory on the machine by storing the same data in memory twice.

If memcached is on seperate infrastructure (which is probably likely), then I guess I would consider what the size of the data stored for the user is going to be. If it is large and you may store a large number of users in the PHP array, it means you could potentially be sucking up more memory on your web server than you find desirable, in which case accessing the data from memcached repeatedly, while being slightly slower for overall access time, would probably provide significant application performance under server load.

Personally, I would probably tend to lean towards relying on memcached for each request, as it is just more scalable.