MySQL has a built-in slow query log. To use it, open the my.cnf file and set the slow_query_log variable to “On.” Set long_query_time to the number of seconds that a query should take to be considered slow, say 0.2. Set slow_query_log_file to the path where you want to save the file. Then run your code and any query above the specified threshold will be added to that file.
Source: How to speed up your MySQL queries 300 times | Opensource.com