Detailed instructions to create a LAMP server using Debian 9 Stretch RC3. Prepare your server for php7 and MariaDB.
October 21st, 2013 247,823
Logs is the best place to start troubleshooting. Concerning MySQL (or MariaDB), you need to refer to: General query Log, Error Log and Slow Query Log
Recently, many popular Linux distributions have moved from MySQL to MariaDB. Think if you have to move to MariaDB in your production servers.
PHP MySQL extension is deprecated. PHP MySQLi extension is Object Oriented, supports Transactions and protects from SQL Injection, using Prepared Statements.