Sharding, pre-allocating leases of blocks of tickets across available resources, and eventual consistency. You don't need to keep the UX transactionally correc

Sharding, pre-allocating leases of blocks of tickets across available resources, and eventual consistency. You don't need to keep the UX transactionally correct; you are able to say "0 tickets remaining" and then a minute or hour or day later say "100 tickets remaining". For something as popular as Taylor Swift, the fans will keep checking.