SERIALIZABLE is really quite hard to retrofit to existing apps; deadlocks, livelocks, and “it’s slow” show up all over the place when you switch it on.

Definitely recommend starting new codebases with it enabled everywhere.

Good call, SERIALIZABLE is a strong option - it eliminates a whole class of bugs at the isolation level. The trade-off is your app needs to handle serialization failures with retry logic, which introduces its own complexity. That retry logic itself needs testing, and barriers work for that too. On randomized testing - that actually has the same limitation you mentioned about barriers: you need to know where to point it. And without coordination, the odds of two operations overlapping at exactly the wrong moment are slim. You'd need enormous pressure to trigger the race reliably, and even then a passing run doesn't prove much. Barriers make the interleaving deterministic so a pass actually means something.