Non-persistent: *370* requests/second Persistent: *525* requests/second This is with MySQL's query cache enabled. But Callgrind shows us that we are actually calling MySQL's internal prepare/execute API. 'mysql', 'db_user' => 'nobody', 'db_pwd' => 'foobar', 'db_host' => 'localhost', 'db_db' => 'users', 'db_opts' => array(PDO::ERRMODE_EXCEPTION => true, PDO::ATTR_PERSISTENT => true, PDO::ATTR_EMULATE_PREPARES=>true) ); ?>]]> PDO::ATTR_EMULATE_PREPARES was added in PHP 5.1.3. You can use PDO::MYSQL_ATTR_DIRECT_QUERY in earlier versions. That brings us to *580* requests/second. Down to 3 servers! The same tests with InnoDB reveal similar numbers. Sqlite3 comes in at around *550* requests/second with persistent connections.