php - How to prevent race condition in online hotel booking - Stack Overflow
One solution is to add two columns to a table in the database. One column is the session ID or user ID or whatever of the user that is being offered the room. The second column is a timestamp indicating when that offer will expire.
Then, in your app, only show rooms that have an expired timestamp in the hold column. (Set the initial timestamp to 0 so that it starts out expired.) When a room is selected, check the column again. If there's an unexpired timestamp there, the user gets a "sorry, you were too slow" message. Otherwise, put a timestamp there for 15 minutes into the future or whatever, and proceed.
You see this on travel sites and ticket-purchasing sites a lot where it says something like "We're holding these seats for you for another 14 minutes. Please complete the transaction by then or it will be released blah blah blah."
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One solution is to add two columns to a table in the database. One column is the session ID or user ID or whatever of the user that is being offered the room. The second column is a timestamp indicating when that offer will expire.
Then, in your app, only show rooms that have an expired timestamp in the hold column. (Set the initial timestamp to 0 so that it starts out expired.) When a room is selected, check the column again. If there's an unexpired timestamp there, the user gets a "sorry, you were too slow" message. Otherwise, put a timestamp there for 15 minutes into the future or whatever, and proceed.
You see this on travel sites and ticket-purchasing sites a lot where it says something like "We're holding these seats for you for another 14 minutes. Please complete the transaction by then or it will be released blah blah blah."
I would also go with the pending state. You could save the state together with the session id of this user and have a cronjob that deletes all pending states that have expired session ids associated to them.
you can add a temporary reservation to the reservations table (with a temp-flag/field) and remove that later if the reservation is not finished after 15 minutes.
additionally if multiple users try to reserve the last room very simultaneously you should again check the availability in every step of the reservation to notify users that the last room has just been taken and propose another roomtype etc.
The classic method to do this is to use a transactional database (so there's no clashes) and to do a tentative allocation of the seat to you that expires after some length of time (e.g., 10 minutes for kiosks) that gives you enough time to pay. If the (customer-visible) transaction falls through or times out, the seat allocation can be released back into the pool. (All state changes are processed via the transactional database, and one customer-visible transaction might require many database-level transactions.)
Airlines will use a similar system (though much more complex due to the need to handle multiple flight legs!) for booking seats online. I would imagine that the timeout would be considerably longer; airline tickets are usually booked further ahead than movie tickets, and are more expensive as well.
