distributed database

ve Exercise 1 Assume that two concurrent executing transactions T1 and T2 are allowed to update same stock item say 'A' in an uncontrolled manner. In such scenario. Give the problems no concurrency module and allows concurrent execution. Exercise 2 Suppose that 2PC with Presumed Abort is used as the commit protocol. Explain how the system recovers from failure and deals with particular transaction T in each of the following cases: (a) A subordinate site for T fails before receiving a prepare message. (b) A subordinate site for T fails after receiving a prepare message but before making a decision (c) The coordinator site for T fails before sending a prepare message, (d) The coordinator site for T fails after writing an abort log record but before sending any further messages to its subordinates