Read Committed: a transaction only sees data that has been committed, preventing dirty reads of another transaction's uncommitted changes. Non-repeatable reads can still occur.
2 / 5
What is a non-repeatable read?
Non-repeatable read: two reads of the same row in one transaction return different values because another committed transaction modified it in between. Repeatable Read prevents this.
3 / 5
What anomaly do phantom reads involve?
Phantom read: re-running a range/predicate query returns newly inserted (or removed) rows that match the condition. Only Serializable fully prevents phantoms in the SQL standard.
4 / 5
Which isolation level is the strictest in the SQL standard?
Serializable: guarantees transactions behave as if executed one after another, eliminating dirty reads, non-repeatable reads, and phantoms at the cost of more contention.
5 / 5
What anomaly is allowed under Read Uncommitted?
Read Uncommitted: the weakest level, permitting dirty reads where a transaction can observe another's uncommitted (and possibly rolled-back) data.