Yes it's the serializable isolation level. For applications targeting upstream SQLite, mvsqlite enables pessimistic locking by default - when a transaction is

Yes it's the serializable isolation level. For applications targeting upstream SQLite, mvsqlite enables pessimistic locking by default - when a transaction is promoted to EXCLUSIVE, it acquires a one-minute lock lease from mvstore. At this point we have the chance to fail gracefully and return a "database is locked" error if multiple clients want to acquire lock on the same DB. This is a best-effort mechanism to prevent conflict on commit (which causes the process to abort). A future feature is "MVCC-aware clients". Compatible clients can opt-in to full, optimistic MVCC, and avoid pessimistic locking. After `COMMIT`, the client should call a SQLite custom function provided by mvsqlite to check whether the commit actually succeeds, and retry if not.