[eknuth]

I would never have thought that MySQL could handle massive databases, but it honestly isn't that bad. You just can't expect it to behave like a normal database.

I had to use mysql to build a 200 million row 200gb database. The trick was using myisam and indexing it as little as possible (just the pk). I used sphinx to handle full text searching. Searching and retrieving records was very fast.

[Tokutek]

Good insight. As to your point -- keeping up many indexes with MyISAM or InnoDB is definitely a problem, especially if the indexes grow too big for RAM. In these cases, TokuDB (http://en.wikipedia.org/wiki/TokuDB), a drop in storage engine replacement for MySQL, can help by replacing dated B-tree technology with more modern Fractal Tree indexes, since B-trees suffer in performance with high insertion rates (especially random insertions) into disk. By allowing for faster write performance, Fractal Tree engines allow for more indexes to be maintained, and hence better query performance can be obtained.