How does memcache with MySQL work?

Question

I am trying to understand (and probably deploy) memcached in our env.

We have 4 web servers on loadbalancer running a big web app developed in PHP. We are already us

Answer 1

Cache, in general, is a very fast key/value storage engine where you can store values (usually serialized) by a predetermined key, so you can retrieve the stored values by the same key.

In relation to MySQL, you would write your application code in such a way, that you would check for the presence of data in cache, before issuing a request to the database. If a match was found (matching key exists), you would then have access to the data associated to the key. The goal is to not issue a request to the more costly database if it can be avoided.

An example (demonstrative only):

$cache = new Memcached();

$cache->addServer('servername', 11211);

$myCacheKey = 'my_cache_key';

$row = $cache->get($myCacheKey);

if (!$row) {

    // Issue painful query to mysql
    $sql = "SELECT * FROM table WHERE id = :id";

    $dbo->prepare($sql);
    $stmt->bindValue(':id', $someId, PDO::PARAM_INT);

    $row = $stmt->fetch(PDO::FETCH_OBJ);

    $cache->set($myCacheKey, serialize($row));
}

// Now I have access to $row, where I can do what I need to
// And for subsequent calls, the data will be pulled from cache and skip
// the query altogether
var_dump(unserialize($row));

Check out PHP docs on memcached for more info, there are some good examples and comments.