someone can correct me but most of the time optimistic locking is ideal (since for most apps, the same data typically has a low chance of being updated by different people). Anyways we use that in addition to transactions

pessimistic locking in general is really tricky

http://www.ibm.com/developerworks/websphere/techjournal/0603...

I forgot to add that if you're using a good framework, it typically already has a built-in mechanism for optimistic locking