Question

When 2 request comes to the database at the exact same time how will it handle it

Answer 1

Even if two cpu's are handling requests at exactly the same time, and they conflict, then at some stage they will say "I want to do something, which can't be done at the same time as anything else is happening". If two cpus do this at exactly the same time, there will be a predefined order - I would imagine that the lowered-number CPU would get priority.