Q:

Should I put my entire site on one database or split into two databases?

My webapp that I am developing will incorporate a forum (phpbb3 or smf), a wiki (doku wiki flat file storage), and my main web app.
All of these will share a User table. The forum I expect to see moderate usage (roughly 200 posts a day) to begin with and will increase from there. The main web app will be used heavily with triggers, mysql events, and stored procedures.
Would splitting the forum and main web app up into separate databases be the wiser choice (IE maintainability and performance)?

A:

Why would you ever use two databases?  What possible reason can there be?  Please update the question to explain why you think two databases has some advantage over one database.
Generally, everyone tries to use one database to keep the management overhead down to an acceptable level.  Why add complexity?

