As web developers, we usually don't have to deal with concurrency bugs much. Everything we need is neatly abstracted and the databases we use carry us for the most part. Concurrency bugs are rare when you just have small or no transactions. However, business apps don't have that luxury, which are always transactional in nature and have long-running transactions. Once you hit a certain number of users, every scenario you think is "rare" will start occurring. You can choose to ignore and maybe man...