ACID Properties In DBMS

ACID Properties 

A-Atomicity
C-Consistency
I-Isolation
D-Durability

Atomicity:

Which monitors either a transaction is completely done or nothing has been done. The following is an example.

Suppose Account A has a balance of 400$ & B has 700$. Account A is transferring 100$ to Account B. This is a transaction that has two operations a) Debiting 100$ from A’s balance b) Creating 100$ to B’s balance. Let’s say first operation passed successfully while second failed, in this case A’s balance would be 300$ while B would be having 700$ instead of 800$. This is unacceptable in a banking system. Either the transaction should fail without executing any of the operation or it should process both the operations. The Atomicity property ensures that.

Consistency:

To preserve the consistency of database, the execution of transaction should take place in isolation (that means no other transaction should run concurrently when there is a transaction already running).

For example account A is having a balance of 400$ and it is transferring 100$ to account B & C both. So we have two transactions here. Let’s say these transactions run concurrently and both the transactions read 400$ balance, in that case the final balance of A would be 300$ instead of 200$. This is wrong. If the transaction were to run in isolation then the second transaction would have read the correct balance 300$ (before debiting 100$) once the first transaction went successful.

Isolation:

If you are in the middle of the transactions other processes wont be able to see the data until the transaction is completed.

Durability:

Once the transaction is commited, even if the system crashes, there should be a way to get back the data.