Why concurrency control matters in PostgreSQL

Introduction

Concurrency control helps multiple users work with the database at the same time without causing mistakes or losing data.

When many people are updating the same bank account balance at once.

When multiple users try to book the last available seat on a flight.

When several employees enter sales data into the system simultaneously.

When a website handles many users posting comments at the same time.

When an online store updates product stock while many customers buy items.

Syntax

PostgreSQL

BEGIN;
-- your SQL commands here
COMMIT;

Use BEGIN and COMMIT to start and end a transaction, which helps control concurrency.

PostgreSQL automatically manages locks to keep data safe during concurrent access.

Examples

This transaction safely subtracts 100 from account 1's balance.

PostgreSQL

BEGIN;
UPDATE accounts SET balance = balance - 100 WHERE id = 1;
COMMIT;

This transaction adds a new order without interference from other users.

PostgreSQL

BEGIN;
INSERT INTO orders (user_id, product_id) VALUES (5, 10);
COMMIT;

Sample Program

This transaction reduces the stock of product 3 by 1 only if stock is available, preventing overselling.

PostgreSQL

BEGIN;
UPDATE products SET stock = stock - 1 WHERE id = 3 AND stock > 0;
COMMIT;

Important Notes

Without concurrency control, data can become incorrect or lost when many users change it at the same time.

PostgreSQL uses locks and transactions to keep data safe and consistent.

Always use transactions when making multiple related changes to the database.

Summary

Concurrency control keeps data safe when many users work at once.

Transactions group changes so they happen all together or not at all.

PostgreSQL helps manage concurrency automatically with locks and transactions.