Backend & systems·Transactions and isolation
your transaction sees the database frozen as of the instant it began, no matter what commits while it runs.
Snapshot isolation
A level where every read comes from a consistent point-in-time snapshot, implemented with MVCC. Readers never block writers and writers never block readers, which is why it is the workhorse of modern databases. It still allows write skew, so it is not serialisable no matter what the level is named in your engine.