Four properties of database transactions
Atomicity (Atomic), consistency (consistency), isolation (isolation), persistence (Durabiliy), for short, ACID
Problems with data concurrency
Dirty read, non-repeatable read, Phantom Read, first class missing update, second category missing update
- Dirty read: Transaction a reads data not mentioned by transaction B
- Non-repeatable READ: Transaction A reads data submitted by transaction B (mostly modified)
- Phantom read: Transaction A reads data submitted by transaction B (mostly new)
- First category missing update: Transaction A revokes data that has already been submitted by transaction B
- Second category missing update: Transaction A overwrites data that has been committed by transaction B
Isolation level of a transaction
- READ uncommitted does not occur when the first category of updates is lost
- Read commited does not occur dirty reads and first class updates are lost
- Repeatable read will only show Phantom reads
- SERIALIZABLE all will not happen
Basic knowledge of database transactions
