Another interesting aspect of seat availability is the number of questions that the airlines must answer. If every passenger poses 100 searches before buying a ticket (a number in line with actual behavior) and each search looks at 1,000 flights, then the airlines would need to answer 15,000,000 questions a second. Neither their networks nor their computers can handle this, a situation that forced ITA Software to develop a sophisticated seat availability caching system. The problem is aggravated by O&D availability: if the entire trip must be included in each query, something many airlines desire, then search becomes impossible because every potential solution must be independently validated with the airline.
Finally, the airlines’ seat availability infrastructure does not include any locking mechanism, so even if an airline responds that a booking code is available, there is no guarantee that by the time a traveler says “yes, I’d like to buy it” it still will be.