This paper proposes a locking protocol which associates locks with sets of resources. This
protocol allows simultaneous locking at various granularities by different transactions. It is
based on the introduction of additional lock modes besides the conventional share mode
and exclusive mode. The protocol is generalized from simple hierarchies of locks to directed
acyclic graphs of locks and to dynamic graphs of locks. The issues of scheduling and
granting conflicting requests for the same resource are then discussed. Lastly, these ideas …