Transactions and rollback and their lack of in viajar.com

This post should be called "I'm going to Akademy! (i hope)", but instead of rejoicing of going for 4th consecutive year to KDE meeting, i'm going to do a rant about transactions and how rollback should work.

So here was I, sitting in my computer trying to find a good flight to go to Gran Canaria and ended up in viajar.com. They had a mixed offer (flight from Barcelona to Gran Canaria with one company and back with a different one) that was the best considering time and money so i went on and bought from them.

So i clicked the "buy" button after filling all the data and scared saw that the server was taking too much time to show me the "done" page. After 5 minutes or so, it told me "error", and i went like "oh, i'll have to find some other place to buy". But first i had a look at my credit card account and saw in horror that a the company of the second flight (clickair) had charged me about the half of the amount of money of what i had bought.

Calm down! I thought, and waited for a mail explaing something, but there was none for 12 hours so i had to call them. A nice person answered and explained me that they had absolutely no record of my purchase so they could not give me any info, i then explained the situation and she realized that clickair bookings are somewhat done differently from the rest because it's a Low Cost Company so she asked me which dates i had booked and promised to give an answer back.

Two hours later she phoned me with the needed data to take both flights as it seems she could book me also the first flight, good, all resolved!

But i was still wondering, how can the system book one ticked without checking the other one is available? how can i get a ticket booked and get no information back? Probably i went to the last if/else/if/else/if/else of conditions, but that's no excuse.

So if you are doing internet "shops" think twice your transactions and rollbacking mechanism, and then, think it a third time!