You could write an abstraction layer to your database code that doesn't rely on what the underlying database is. Then if you find that MySQL isn't good enough for your purposes, you can switch to something else and only have to change the database portion of your code.

Personally, I haven't ever had any problems with MySQL for things. With any DBMS, you are going to need to know how to efficiently model the data as well as using the proper indexes to tune the performance.

There is also Postgres, which I haven't used myself.

Oracle also runs on linux and is a pretty robust DBMS, but I think the license only allows you to use it without paying for learning purposes. If you were to use it in a final product, you would likely need to pay a pretty hefty fee. You'd have to check on that to be sure, though.

MySQL is quite resilient, particularly if you cluster it. There's also Postgres, which has some things that MySQL doesn't. It used to not perform as well, but that may have changed in recent years. You can also go with Oracle if you have RH (or are willing to put up with lots of pain). IIRC there's a free download, but with no support, and Oracle is extremely non-trivial to get working right with no support (from what I've read).

Anyhow, you could use ODBC code and then you're not tied to a particular database, or partition out your database access to a signle module, so if you change, you only have to re-code one module (if you need DB specific features that can't be had with ODBC). This is good programming practice anyhow.

Yes, you can use C++ to get user info from a Web page, as CGI scripts can be written in any language. If you don't want to go the CGI routes, there are other, more esoteric ways.

Dude you don’t have to worry until and unless you are crossing in limits in terabytes. Let me give an example http://en.wikipedia.org/wiki/Main_Page has about 170GB of data in mysql on 9 October 2004 (see h/w info http://meta.wikimedia.org/wiki/Wikimedia_servers) , excluding images and multimedia!

Also see http://en.wikipedia.org/wiki/Wikipedia:Technical_FAQ