One of the main requirements for a fast web server is to has efficient and effective SQL server. If you having the slow mysql service, and you are out of idea where gone wrong, you can actually try is enable slow query log.
Sometime, a single SQL query may be the cause of all the server’s problems.
To enable slow query log, simply add the following line to MySQL configuration file (my.cnf or my.ini), and then restart the MySQL server:
log-slow-queries = [path to the log file]