| Level | Anomaly Prevented | Concurrency Impact | |-------|-------------------|--------------------| | READ UNCOMMITTED (or NOLOCK hint) | None (dirty reads possible) | High (no shared locks) | | READ COMMITTED (default) | Dirty reads | Medium (locks held briefly) | | REPEATABLE READ | Non-repeatable reads | Lower (holds locks until end of transaction) | | SERIALIZABLE | Phantom reads | Very low (range locks) | | READ COMMITTED SNAPSHOT (RCSI) | Dirty reads via row versioning | High (no locks for readers) |
Happy coding. May your seeks be narrow and your scans be none. sqlserver developer