Understanding the SERIALIZABLE Isolation Level in SQL

Last update on October 04 2025 12:40:21 (UTC/GMT +8 hours)

Demonstrate Isolation Level SERIALIZABLE

Write a SQL query to demonstrate the SERIALIZABLE isolation level.

Solution:

-- Set the isolation level to SERIALIZABLE.
SET TRANSACTION ISOLATION LEVEL SERIALIZABLE;

BEGIN TRANSACTION; -- Begin the transaction.

-- Read data from the Employees table.
SELECT * FROM Employees WHERE DepartmentID = 1;

-- Simulate another transaction attempting to modify the same data.
UPDATE Employees SET Salary = 60000 WHERE DepartmentID = 1;

COMMIT TRANSACTION; -- Commit the transaction.

Explanation:

Purpose of the Query :

The goal is to demonstrate how the SERIALIZABLE isolation level ensures complete isolation by locking the data until the transaction is complete.

Key Components :

SET TRANSACTION ISOLATION LEVEL SERIALIZABLE : Sets the isolation level.
SELECT and UPDATE : Demonstrates reading and modifying data within the transaction.

Why Use SERIALIZABLE? :

This isolation level provides the highest level of isolation, preventing dirty reads, non-repeatable reads, and phantom reads.

Real-World Application :

For example, in financial systems, you might use this isolation level to ensure that transactions are fully isolated and consistent.

Additional Notes:

The SERIALIZABLE isolation level is the strictest but can lead to performance issues due to locking.
Scenarios where SERIALIZABLE is appropriate include:

Critical operations where data consistency is paramount.
Situations where concurrent transactions must not interfere.

Important Considerations :

Use SERIALIZABLE sparingly, as it can cause contention and reduce throughput.

For more Practice: Solve these Related Problems:

Write a SQL query to demonstrate how the SERIALIZABLE isolation level prevents phantom reads in a database.
Write a SQL query to simulate two concurrent transactions attempting to modify the same data under the SERIALIZABLE isolation level.
Write a SQL query to test the locking behavior of the SERIALIZABLE isolation level when reading and updating data simultaneously.
Write a SQL query to compare the performance impact of the SERIALIZABLE isolation level versus other isolation levels in a high-concurrency scenario.

Go to:

PREV : Demonstrate Isolation Level READ COMMITTED.
NEXT : Rollback a Failed Transaction.

Have another way to solve this solution? Contribute your code (and comments) through Disqus.