How to prevent overbooking through PostgreSQL when booking the last seat simultaneously?

To prevent overbooking (booking the same last seat by multiple users simultaneously) in PostgreSQL, several approaches can be used:

1. Transactions with SERIALIZABLE isolation level — ensure that transactions are executed sequentially, preventing conflicting changes.

2. Row locking (SELECT ... FOR UPDATE) — when attempting to book a seat, first lock the corresponding record so that other transactions wait for the current one to finish.

3. Unique constraints and availability checks — for example, store the seat status and check if it is free during booking, updating the status within a single transaction.

Example using row locking:

BEGIN;
-- Lock the seat record for update
SELECT * FROM seats WHERE seat_id = :seat_id AND status = 'available' FOR UPDATE;

-- If the record is found, update the status
UPDATE seats SET status = 'booked' WHERE seat_id = :seat_id;

COMMIT;

If two requests try to book the same seat simultaneously, the second will wait until the first completes, and if the seat is already booked, the update will not occur.

It is also important to handle errors and retry booking attempts in case of transaction conflicts.