The text was something that database is not available.
Forum address had SMF database something and main site had a box with text, database something also.
So my thinking was that one service does them all.
Ah, no, there is a full stack needed for any dynamic website application like this forum.
1. The HTTP server itself, provides static content like images, but also hands off dynamic requests to another service where required, which brings us to;
2. PHP, this service runs the application itself, in this case SMF, which is written in PHP, however it needs a very fast method of storing and retrieving data, as such we have specialised applications for that, called a database.
3. The Database, or MySQL in our case. This is a service dedicated to the fast storage and retrieval of mass amounts of data. It's highly optimised for this specific purpose and designed to be extremely fast and reliable.
If any one of these three layers breaks down, the forum will stop functioning correctly.
As we are running a clustered setup, there are actually a few extra intermediate layers to deal with failures or high loads.
This forum is one of the largest SMF forums on the internet with an extremely active user base. Keeping it running fast and responsive for so many concurrent users is no easy feat. It doesn't help that the SMF developers (and most forum developers) have little to no experience with forums of this size, as such, scaling it to work in a cluster can become quite tricky.
Edit: If you're talking about running a separate server for the website and a separate one for the forum, it makes little sense to do so from a technical point of view, and would substantially increase Dave's hosting costs.