Read committed behavior in PostgreSQL

Introduction

Read committed behavior ensures you only see data that has been saved by others. It helps avoid confusion from unfinished changes.

When you want to read data that is stable and not being changed right now.

When you want to avoid seeing partial updates from other users.

When you want your queries to reflect the latest committed changes.

When you want to prevent reading data that might be rolled back later.

Syntax

PostgreSQL

SET TRANSACTION ISOLATION LEVEL READ COMMITTED;

This command sets the transaction to read committed mode.

In PostgreSQL, this is the default isolation level.

Examples

This starts a transaction, sets read committed mode, reads data, then ends the transaction.

PostgreSQL

BEGIN;
SET TRANSACTION ISOLATION LEVEL READ COMMITTED;
SELECT * FROM employees;
COMMIT;

This sets the isolation level for the current transaction only.

PostgreSQL

SET TRANSACTION ISOLATION LEVEL READ COMMITTED;

Sample Program

This example reads the product with id 1 using read committed isolation to ensure the data is stable.

PostgreSQL

BEGIN;
SET TRANSACTION ISOLATION LEVEL READ COMMITTED;
SELECT * FROM products WHERE id = 1;
COMMIT;

Important Notes

Read committed isolation prevents dirty reads but allows non-repeatable reads.

It is the default level in PostgreSQL, so you usually don't need to set it explicitly.

Summary

Read committed shows only saved data from other transactions.

It avoids reading unfinished changes (dirty reads).

This level is good for most everyday database reads.