SQLite Begin Concurrent
I don't know how I feel about this implementation. On the one hand, I love its simplicity and the fact that you still have Serializable transactions. On the other hand, having conflicts at the page level means that the occurrence of conflicts may be surprising because it's based on this fuzzy notion of having values "close together". Close together changes based on your page size configuration and, as the article points out, is not necessarily correlated with a natural key in ROWID tables. I would be very interested to see this system in use in a few real applications to get an sense of how much this really matters.