Question

so suppose I connect to mysql with my php script as usual, but then suppose I never actually call any code that would close that connection and just let it be until the page is served to the user

Is there any reason why I shouldn’t be doing this? What negative consequences may arise (if any) if I do this?

Answer 1

Depending on the mysql extension you are using not closing the connection is actually beneficial as this will allow the use of persistent connections. That means the connection is only opened the first time the script runs, and every subsequent run the already-open mysql connection is used, reconnecting as needed. This is a bit faster and less resource intensive then opening and closing the connection on every single request. If you are using mysqli then persistent connections should be possible and are preferable.

Even if your mysql extension doesn’t support persistent connections, or isn’t configured to use them, that just means the connection will close when the script exits, which is no different than closing it yourself, which means closing it manually gains you nothing.

Conclusion: closing the connection yourself probably gains you nothing and might actually hurt performance.

edit: See mysql.allow_persistent and mysqli.allow_persistent to configure whether or not persistent connections are used for mysql, depending on which mysql extension you are using.