Isolation Levels — Complete Guide
Isolation Levels — 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 43 of 100
Isolation Levels
Basics ✓ → Advanced
Advanced · 2 — Production · ~6 min · MySQL — Transactions & Concurrency
What is this?
Isolation levels control how much one transaction sees of others’ uncommitted or in-flight changes: READ UNCOMMITTED, READ COMMITTED, REPEATABLE READ (MySQL default), SERIALIZABLE.
Why should you care?
Two agents updating the same Swiggy rider payout row need predictable reads — wrong level causes double pay or stale totals.
See it live — copy this example
Run in MySQL Workbench or the mysql CLI.
SET SESSION TRANSACTION ISOLATION LEVEL READ COMMITTED;
START TRANSACTION;
SELECT balance_inr FROM accounts WHERE account_id = 1;
-- Another session may commit a change before your next SELECT
COMMIT;What happened?
- READ COMMITTED allows non-repeatable reads — second SELECT in same txn may differ.
- REPEATABLE READ snapshots first read for the transaction duration in InnoDB.
Practice next
- Open two Workbench tabs on DataFlow.
- Tab A: START TRANSACTION; SELECT balance.
- Tab B: UPDATE balance; COMMIT.
- Try SERIALIZABLE on a contested UPDATE — note locks.
- SHOW VARIABLES LIKE 'transaction_isolation';
Remember
Default InnoDB is REPEATABLE READ. Higher isolation = fewer anomalies, more locking. SET SESSION for testing; change global only with DBA review.
DataFlow payout job
Batch job uses REPEATABLE READ so rider totals stable during 10-minute run.
Outcome: No partial updates skew payroll.
Interview prep for this lesson
Practice these questions aloud after reading—each links to a full structured answer.
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