Understanding the SERIALIZABLE Isolation Level in SQL

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.

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

Previous SQL Exercise: Demonstrate Isolation Level READ COMMITTED.
Next SQL Exercise: Rollback a Failed Transaction.