First, is there a limit to the number of posts a category may have?
Second, does the number of sub-categories, and sub-sub-categories make a difference in forum speed? For instance, is there a speed difference between having 500,000 posts spread between 50 Master categories versus 50 Sub-Categories off 1 Master category?
1) - Nope the only limit you would have is if your database was too big to fit on the hard drive of your host's server.
2) - I would say no to this one. All the categories are, are just different id's in the database labeled to each post/thread. Making a subforum just changes how it displays the forum layout and the posts.
I tried adding a bunch of subcategories but it really slowed down. With only a few main categories (~5) a page load took about .04s.
But when I had a Main Category, 50 Sub Categories (one for each state), and each stat sub category has about 4 categories of itself (ex., Main->Ohio->cat1,2,3,4) the page load slowed to a crawl at .16s. This is with no posts or users except for myself.
Shouldn't the result list be cached or something because this spike from .04 to .16 seems off to me. What are your thoughts, I am a newb to myBB and maybe this is normal with this many categories.
Forums are cached. The forum jump list is what would take a while to load, viewing a forum that is 100 parents deep shouldn't be slow. I tried it on my localhost once, had a forum 100 forums deep, ran just as fast as any other page once I disabled the forum jump.