8. Transaktioner og låsning/låse. Herunder ACID egenskaberne.
Uden transaktion Session 1Session 2Account Balance myBalance = Read(balance)100 myBalance = Read(balance)100 Write (myBalance += 10)110 Write (myBalance -= 100)0
Med transaktion Session 1Session 2Account Balance Begin Transaction ->Starter100 myBalance = Read(balance)100 Begin Transaction -> Venter100 Write (myBalance += 10)110 End Transaction110 Kan starte transaktion110 myBalance = Read(balance)110 Write (myBalance -= 100)10 End Transaction10
Deadlocks Session 1Session 2Account1Account2 Begin Transaction1 - >Starter myBalance = Read(account1) Begin Transaction2 -> Starter Begin Transaction2 -> Venter myBalance = Read(account2) End TransactionBegin Transaction1 -> Venter Deadlock !!