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

My webapp that I am developing will incorporate开发者_JAVA技巧 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)?

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?

Keep your app simple to begin with. If you're not expecting a huge amount of traffic to begin with, then it's fine to have a single database. You can always upgrade your site later. Changing which database a table is stored in shouldn't require a huge amount of code.

It depends. If there is any chance of optimization, then splitting is good not otherwise. Another thing is that even if you split, you should be able to manage them all successfully, a bit of overhead.

For the sake of maintainability in the future, I would definitely recommend against splitting DBs when you have a shared table. This will only serve to increase the size of your queries (since joins across DBs will require further qualification). This also will eventually lead to confusion when someone new can't figure out why their query doesn't work.

Furthermore, if the two DBs are actually running on separate servers or instances, you won't be able to join and will be forced to move back and forth between code and query to do something that would otherwise be a simple join. That may not be a big deal for a simple one row look up type queries, but for more complicated summary type queries, it means dumping off a lot of the processing that RDBMs' are specifically optimized for into your more general purpose programming language.

separating to two database could not guarantee performance. putting tables in different tablespace (i.e. different drives) could boost performance, as independent queries doesn't often compete for hard disk's read/write head's access turns