Read Committed
Read committed prevents dirty reads: a transaction sees only data other transactions have committed, but non-repeatable reads and phantom reads are still allowed.
Purpose
To provide a moderate isolation level balancing consistency against concurrency; the default of most DBMSs.
Mechanism
Reads return only committed rows (via row locks or MVCC visibility checks). Two reads within the same transaction may differ (another transaction committed new data). The PostgreSQL/Oracle default level.
Use cases
- Database default isolation
- Dirty read defense
- Isolation level selection