Their problem stemmed from having MyISAM as their default storage engine for session data, and with it’s table-level locking, it only needs a few thousands users to hit the site at the same time to bog down MySQL. The solution? InnoDB storage engine with its row-level locking feature. Of course, it’s worth noting that InnoDB supports a bunch of features that a real database should have including transactions and enforced referential integrity.

Go ahead and read the complete Free Performance with MySQL Table Types article and learn how the big boys do it