Here’s a MySQL tip from the MySQL Performance Blog which deals with possible lock situations while using InnoDB and foreign keys.

Today I was working with application which uses Innodb and foreign keys and got into locking problems possibly due to foreign keys, so I did a little investigation on that matter.

Peter Zaitsev goes on to outline an example of when this could happen and warns developers to look at locking overheads while implementing foreign keys in Innodb

Link: MySQL Performance Blog » Innodb locking and Foreign Keys