which programming language does Facebook use for its different parts

I am wondering what programming language (Php, Ajax, ...) facebook uses. What kind of database server? for "view older posts"? what considerations for high traffic and security? Can anybody help me? Thanks a lot.

PHP. http://developers.facebook.com/blog/post/358

Facebook use MYSQL for its DBMS. the node of MYSQL over than 2000 node. "for older posts" it maybe also use this DBMS and use AJAX for increase its efficiency for loading from database.

One way to find out what a site/company uses is to look at their open positions, facebook has several listed here: http://www.facebook.com/careers/department.php?dept=engineering