Handling the concurrent request while persisting in oracle database?

Question

I have this scenario ,on a airline website (using Java) two separate customers send two requests at same time to book a same seat in same airline
from New York to Chica

Answer 1

As you mention, transanction settings will help you achieving one operation. The best way to enforce this kind of restrictions it to ensure that your relational model is constrained not to accept the 2nd operation once the 1st one succeeds.

Instead of having to do an update on a row, say update .... seat = "taken", create a reservation table (customer, flight, seat) which has a constrain (column:seat = unique) (lookup ora docs to learn the syntax for that on table creation). That way your reservation process becomes an insert in the reservation table and you can rely on the RDBMS to enforce your relational constrains to keep your business model valid.

e.g. Let t1 be the earlier operation time, you'll have:

t1=> insert into reservations(customer1,flight-x,seat-y) // succeeds. Customer 1 reserved the seat-y
t2=> insert into reservations(customer2,flight-x,seat-y) // fails with RDBMS unique constrain violated.

The only way to reserve seat-y again is to first remove the previous reservation, which is probably what your business process wants to achieve.