what is ACID Properties in DBMS Explained
What is ACID Properties..?
During my college days, I always had a hard time to understand ACID properties in DBMS.
I was aware that -
A stands for Atomicity
C stands for Consistency
I stands for Isolation
D stands for Durability
but I could not relate things and understand this at all.
I explored it in detail while I was working for Cisco and let me present that with simple examples.
Let's assume you have a HDFC saving bank account & You have 25k in your account.
Minimum balance in account should be 5k
Consider, you are trying to transfer some amount to your friends account.
This involves 2 activities -
1. money deducted from your account
2. money added to your friends account
what if first activity succeeds and second one fail?
Money will be deducted from your account,
also your friend has not yet received the amount.
this will lead the system in a wrong/inconsistent state
1) Atomicity: It says either both the above activities happen as a whole or none of the activity happens. so that we never end up in an inconsistent state.
2) Consistency: lets say you want to transfer Rs 25000,
if the transaction goes through it will lead the system in an Inconsistent state as the balance will be 0 now,
and min balance should have been 5k
3) Isolation - you are transferring 10k to your friend
so first your account gets deducted - at time t1
later, your friend account get added with 10k - at time t3
what if a new reader tried to get your account balance and your friends account balance at time t2 which is in between t1 and t3?
If there is no isolation that person will see wrong data (money deducted from your account, but not added to your friends account)
A new reader should only see it this when both the above activities are done. This is called Isolation.
4) Durability means the committed changes should not be lost even in case of any failures.
I tried my best to explain you in simple layman terms!