- Atomic, a transactions is all or nothing, if one part of a transaction fails then the entire transaction fails.
- Consistent, the database will go from one valid state to another.
- Isolation, concurrent execution of transactions result in a system state that would be obtained if transactions were executed serially.
- Durability, Once a transaction has been commited it will remain so.
Transaction Isolation levels
These are levels that define how isolated the Isolation property of a transaction is. Note they are transactions specific, different transactions can have different isolation levels.
- Statements can not read data that has been modified but not yet committed by other transactions.
- No other transaction can modify data the has been read by the current transaction unitl the current transaction completes.
- Other transactions cannot insert new rows with key values that would fall in the range of keys read by any statement in the current transaction.
- Statement can not read data that has been modified but not yet committed by other transactions ( No dirty reads ).
- No other transaction can modify data the has been read by the current transaction.
Note You can get phantom rows as inserts from other transactions are allowed.
- Statements can not read data that has been modified but not commited by other transactions ( No dirty reads).
Note Data can be changed by other transactions between individual statements within the current transaction resulting in nonrepeatable reads ( Phantom Data ).
- Statments can read rows that have been modified by other transactions but not yet committed.