 between our call to WATCH and
our call to EXEC, the transaction will fail.<br/><br/>We'll have just to re-iterate the operation hoping this time we'll not get
a new race. This form of locking is called <b>optimistic locking</b> and is
a very powerful form of locking as in many problems there are multiple
clients accessing a much bigger number of keys, so it's very unlikely that
there are collisions: usually operations don't need to be performed
multiple times.<h2><a name="WATCH explained">WATCH explained</