Isolation Levels
Level 3
Serializability: Realized by strict 2PL with table level locks
Level 2
Level 3 without coarse grain lock
Repeatable Read: Realized by strict 2PL with tuple level locks only
Phantom tuples may occur
Level 1
Level 2 without share locks
Cursor Stability: Realized by strict 2PL with tuple level exclusive locks only
- Same query executed twice in a transaction can produce different answers
- No repeatable read
Level 0
No locks
- Transaction queries may read uncommitted updates