Define granularity, hierarchy of granularity of locks & multiple granularity locking. Explain the modified two phase locking along with multiple granularity locking.
Ans: The size of the data item selected as a unit of protection through a concurrency control protocol is granularity.
When the granularity is denoted in a hierarchical structure in which each node denotes data items of different sizes we acquire the hierarchy of granularity.
In multiple granularity locking there are three kinds of locks - shared, exclusive and intention lock.
Modified two-phase locking strategy
1) No lock can be granted once any node has been unlocked
2) No node might be locked till its parent has an intention lock
3) No node might be unlocked till all its descendants are unlocked.