In the context of concurrency control, explain with a suitable example what is meant by the temporary update problem. 

Outline the two phase locking approach to concurrency control and show that it guarantees conflict serializability. 

With respect to database recovery, what is meant by a commit point? 

In distributed databases, the database items are distributed across a number of sites with some items replicated across a number of site. Outline an approach that could be used to commit transactions in such a system.