isolation-anomalies
Installation
SKILL.md
Transaction isolation anomalies
Isolation levels are commonly taught as a ladder of "how much locking". That framing causes real bugs. Levels are defined by which anomalies they permit, and two databases can use the same label for different guarantees.
| Label | Actual guarantee |
|---|---|
Postgres REPEATABLE READ |
Snapshot isolation |
MySQL InnoDB REPEATABLE READ |
Snapshot reads plus next-key locks on writes, a different anomaly set |
Oracle SERIALIZABLE |
Snapshot isolation, not serializable |
Postgres SERIALIZABLE |
Genuinely serializable (SSI), aborting transactions to stay so |
Never reason from the label. Reason from the anomaly table.