ACID Properties — Complete Guide
ACID Properties — Complete Guide: free step-by-step lesson with examples, common mistakes, and interview tips — part of MySQL Tutorial on Toolliyo Academy.
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MySQL Tutorial · Lesson 42 of 100
ACID Properties
Basics ✓ → Advanced
Advanced · 2 — Production · ~6 min · MySQL — Transactions & Concurrency
What is this?
ACID: Atomicity (all or nothing), Consistency (rules hold), Isolation (concurrent sessions behave predictably), Durability (committed data survives crash). InnoDB aims for ACID on transactions.
Why should you care?
UPI debit without credit violates consistency — banks rely on ACID so ledgers never show money that vanished mid-transfer.
See it live — copy this example
Run in MySQL Workbench or the mysql CLI.
START TRANSACTION;
UPDATE accounts SET balance_inr = balance_inr - 500 WHERE account_id = 1;
UPDATE accounts SET balance_inr = balance_inr + 500 WHERE account_id = 2;
-- Both must succeed or neither
COMMIT;What happened?
- Atomicity: both updates commit together.
- Consistency: balances stay non-negative if CHECK exists.
- Isolation level controls what other sessions see mid-flight.
- Durability: redo log persists after COMMIT.
Practice next
- CREATE accounts with balance_inr and CHECK >= 0.
- Run transfer transaction successfully.
- Simulate failure: bad account_id on second UPDATE then ROLLBACK.
- Add insufficient funds CHECK and test failed debit.
- Compare READ COMMITTED vs REPEATABLE READ behavior (next lesson).
Remember
Atomicity = complete transaction or none. Consistency = constraints and invariants hold. Isolation + durability are tunable but never ignored in finance.
DataFlow wallet transfer
P2P send uses one transaction debiting sender and crediting receiver.
Outcome: Balances always sum correctly after each transfer.
Interview prep for this lesson
Practice these questions aloud after reading—each links to a full structured answer.
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