I am making a site where users will be able to chat with each other in person-to-person chats and group chats like on facebook, and I would like to ask a few questions before I actually dig in and start coding.
I thought about creating the chat application with javascript, ajax and php, and the conversations will be saved with mysql (PDO with prepared statements connecting to the database). Are these good for doing an application like this, or are there some languages more fitting for this?
Secondly, I fear that if many users would be logged in at the same time, it would make the site slower. Is mySQL really a good RDBMS when there are many users on a site, and are there some methods like PDO but that are intended to do querys faster?