1. Transaction_read_uncommitted- Allows a method to read uncommitted data from a DB(fast but not wise).

2. Transaction_read_committed- Guarantees that the data you are getting has been committed.

3. Transaction_repeatable_read - Guarantees that all reads of the database will be the same during the transaction (good for read and update operations).

4. Transaction_serializable- All the transactions for resource are performed serial.