I'd also like to thank the other for his attempt at raising the general awareness of transaction isolation. Even when you deal with simpler databases like SQLite, isolation is a serious topic. When serializing accesses hinders performances, dealing with the "WAL mode" that grants SQLite with single-writer-multipler-readers abilities is everything but trivial, because of the huge amount of documentation that has to be read in order to reach the desired level of isolation. I've written an SQLite library in Swift that provides by default the snapshot isolation level which grants most developers with both peace of mind, and non-blocking reads. Check out its "concurrency guide" if you're interested: https://github.com/groue/GRDB.swift/blob/master/README.md#co...
Unique to GRDB.swift, as far as I know, is the ability to perform database writes and then wait until snapshot isolation has been reached in another connection before releasing the writing lock. This allows to read from a known database state, while allowing other writes to be performed. The ability to read for a precisely known database state allows nice features like database observation and reactive patterns, while taking advantage from the WAL mode by not holding locks longer than necessary.
