I moved a database recently.
The complete size was in excess of 200MB
Of that though, around 140MB was accumulated stats. The rest was posts/comments.
Very popular blog and there was no slowdown at all.
Databases are remarkably good at managing the data inside them. Even if you have hundreds of thousands of posts, MySQL should not have any real difficulty selecting the bits necessary for each individual page.
“Databases are remarkably good at managing the data inside them.”
It is sort of their claim to fame, isn’t it. :)
