Consider a database system that includes an atomic increment operation, in addition to the read and write operations. Let V be the value of data item X.
The operation increment(X) by C sets the value of X to V + C in an atomic step. The value of X is not available
to the transaction unless the latter executes a read(X).
Assume that increment operations lock the item in increment mode using the compatibility matrix in Figure 18.25.
a. Show that, if all transactions lock the data that they access in the corresponding mode, then two-phase locking ensures serializability.
b. Show that the inclusion of increment mode locks allows for increased concurrency.