MVCC mental model in PostgreSQL - Mini Project: Build & Apply

Understanding MVCC Mental Model in PostgreSQL

📖 Scenario: You are managing a small library database where multiple users can borrow and return books at the same time. To keep track of book availability without conflicts, PostgreSQL uses a system called MVCC (Multi-Version Concurrency Control).This project will help you understand how MVCC works by creating a simple table and simulating transactions that show how PostgreSQL handles concurrent data access.

🎯 Goal: Build a simple PostgreSQL table for books and simulate transactions to see how MVCC manages data versions and visibility.

📋 What You'll Learn

Create a table named books with columns id (integer primary key) and title (text).

Insert three specific book records into the books table.

Set a transaction isolation level to READ COMMITTED to observe MVCC behavior.

Write a query to select all books visible in the current transaction.

💡 Why This Matters

🌍 Real World

MVCC is used in real-world databases to allow many users to read and write data at the same time without conflicts or locking delays.

💼 Career

Understanding MVCC helps database administrators and developers optimize performance and avoid data anomalies in multi-user applications.

1

Create the books table

Write a SQL statement to create a table called books with two columns: id as an integer primary key and title as text.

PostgreSQL

-- Your code here to create the books table

Need a hint?

Use CREATE TABLE books (id INTEGER PRIMARY KEY, title TEXT); to create the table.

2

Insert initial book records

Insert three books into the books table with these exact entries: (1, 'The Hobbit'), (2, '1984'), and (3, 'Pride and Prejudice').

PostgreSQL

CREATE TABLE books (
    id INTEGER PRIMARY KEY,
    title TEXT
);
-- Insert the three book records here

Need a hint?

Use a single INSERT INTO books (id, title) VALUES statement with all three rows.

3

Set transaction isolation level

Write a SQL command to set the transaction isolation level to READ COMMITTED to observe MVCC behavior in PostgreSQL.

PostgreSQL

CREATE TABLE books (
    id INTEGER PRIMARY KEY,
    title TEXT
);

INSERT INTO books (id, title) VALUES
(1, 'The Hobbit'),
(2, '1984'),
(3, 'Pride and Prejudice');

-- Set transaction isolation level here

Need a hint?

Use SET TRANSACTION ISOLATION LEVEL READ COMMITTED; to set the isolation level.

4

Select visible books in current transaction

Write a SQL query to select all columns from the books table to see which rows are visible in the current transaction.

PostgreSQL

CREATE TABLE books (
    id INTEGER PRIMARY KEY,
    title TEXT
);

INSERT INTO books (id, title) VALUES
(1, 'The Hobbit'),
(2, '1984'),
(3, 'Pride and Prejudice');

SET TRANSACTION ISOLATION LEVEL READ COMMITTED;

-- Select all books visible in this transaction

Need a hint?

Use SELECT * FROM books; to see all visible rows.