CA 34 - Atomicity - Design a Reliable Wallet Transfer System with ACID Guarantees

Today I worked on a wallet system like GPay or PhonePe, where users can send money to each other. The main focus was Atomicity from ACID properties.

Atomicity means “all or nothing”.
If a transaction fails in between, everything should go back to the original state.

Transaction
I wrote a transaction like this

BEGIN;
UPDATE accounts
SET balance = balance - 200
WHERE name = 'Alice';
UPDATE accounts
SET balance = balance + 200
WHERE name = 'Bob';
COMMIT;

Now Testing Failure

I intentionally broke the second query (credit to Bob).

BEGIN;

UPDATE accounts
SET balance = balance - 200
WHERE name = 'Alice';
UPDATE accounts
SET balancee = balance + 200
WHERE name = 'Bob';
COMMIT;

BEGIN - start transaction
Do all operations
If success - COMMIT
If error - ROLLBACK

Atomicity ensures no partial transactions, which is very important in payment systems.