비동기 DB

• http://php.net/manual/en/mysqli.query.php
• http://php.net/manual/en/mysqli.reap-async-query.php
• http://blog.ulf-wendel.de/2012/non-blocking-insert-with-mysqlnd/
• https://gist.github.com/attozk/5ddf1e4acb6f76f24478
• https://mariadb.org/mariadb-non-blocking-client-api-and-node-js/