Client/MemcacheClient.php
public function set($key, $value, $ttl)
    {
        if ($this->isSafe()) {
            $key = $this->prefix . $key;
            return $this->mem->set($key, $value, $this->compression, $ttl);
        }

        return false;
    }
public function set($key, $value, $ttl)
    {
        if ($this->isSafe()) {
            $key = $this->prefix . $key;
            return $this->mem->set($key, $value, $this->compression, $ttl);
        }

        return false;
    }
Add a value to the memcache

@param string $key Unique key
@param mixed $value A value. I recommend a string, be it serialized or not - other values haven't been tested :)
@param int $ttl Number of seconds for the value to be valid for
@access public
@return void