I think the most important question is how many users are on your website at the same time (so how many database connection they create at the same time)
- I would suppose this is the most right opinion from the above said. We need archiving feature, if for example, your forums contain about 200,000 posts and they begin to work slower (for some reason - but hardware is the first!), specially Search feature or Latest Discussions. In that case, we need to create SEPARATE tables, so old data is moved from the "main" tables, which will be executed much more often than archived tables. For example, if we have for main tables
then for the archived stuff, we will have
Brazilian forums mentioned do not use the stuff like described. All posts are still saved in the same tables, I asked Sam sometimes about that stuff, and he replied this is just mod_rewrite + some easy script thing. Nothing complicated, but nothing also related to "real" archives.
Anyway, with miniBB's fast engine, it's not urgent to create such kind of archives, so we are not hurrying with that feature. As you see, million-posts forums are running ok, because they are on a powerful dedicated server and good line; forums at radioscanner.ru which I develop, are expecting thousands of visits daily and contain more than 150,000 open posts, but they are still running very good on a virtual hosting, and they all contain the same functions as default miniBB (despite they are "advanced" with additional features a lot).
So this is just the question of good hardware, good connection and good moderation. We on miniBB.com are going to re-arrange our own forums, remove old necessary posts completely, because it should be done once per 2-3 years, if you carry about the content.