Describe the 3 common problems encountered while maintaining concurrency control.
Concurrence control ensures Serializabilty in a multiple user database. The first common problem is lost updates which occurs when data an operation from T2 uses un committed date from the same table of transaction T1. The uncommitted date problem arises when two transactions T1 and T2 are executed concurrently but the T1 is rolled back after T2 used data from T1. Inconsistent retrievals occur when a transaction calculates aggregate functions while a second transaction updates those functions in real time.