Deadlock And Bad Users

How deadlock occurs

Imagine 100,000 transactions all trying to update the same row of the same table in the same database. Somebody is bound to get deadlocked. Once a single transaction with a lock on the user’s profile gets hung (because of the need for a connection from a different resource pool), all the other database transactions on that row get blocked. Pretty soon, every single request-handling thread gets used up with these bogus logins. As soon as that happens, the site is down.

So one group of bad users just blunder around leaving disaster in their wake. More crafty sorts, however, deliberately do abnormal things that just happen to have undesirable effects.