> So, you say that I can modify for 30 minutes a document and then I try to
> see if I can commit the changes?
> I need to know that I can comit the changes before I begin to modify the
> doc. It is like pessimistic locking but without any record lock.

- start transaction
- read the record you want to modify using SELECT ... WITH LOCK
(which will fail in case other user is already editing it)
- play with document
- when done, update the record
- commit

Ivan