How to enable row-level security (RLS) in PostgreSQL

What is Row-Level Security (RLS)?

Row-level security (RLS) is a feature in PostgreSQL that allows you to define policies to restrict access to individual rows in a table. This ensures that users can only access or modify data that they’re authorized to see.

Enabling RLS on a table

First, let’s turn on RLS for a specific table. Here, I’ll assume a table named employees.

ALTER TABLE employees ENABLE ROW LEVEL SECURITY;

By default, this will block all access to the table unless a policy is applied. To still allow the table owner access, you can use:

ALTER TABLE employees FORCE ROW LEVEL SECURITY;

Create an RLS policy

A policy dictates what data can be accessed by whom. Let’s create a policy to allow users to see only the rows where the department matches their role.

CREATE POLICY employee_policy
    ON employees
    FOR SELECT
    USING (department = current_setting('my_app.user_role'));

Apply an RLS policy to table

After creating a policy, apply it to the table using ALTER TABLE.

ALTER TABLE employees FORCE ROW LEVEL SECURITY;
ALTER TABLE employees ALTER POLICY employee_policy USING (department = current_setting('my_app.user_role'));

Test RLS

You can test whether RLS is working by changing the current setting for the role and trying a SELECT query.

SET my_app.user_role = 'Engineering';
SELECT * FROM employees;

Using variables for dynamic RLS policies

You can use session variables to make the policies dynamic.

ALTER TABLE employees ALTER POLICY employee_policy USING (department = current_setting('my_app.user_role'));

Then, whenever a user logs in, set the session variable to their role.

SET my_app.user_role = '<user-role>';

When to Use RLS

RLS is best for multi-tenant applications or applications with different user roles that require access to subsets of data. It’s not recommended for systems with extremely high throughput because it might add performance overhead.

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Alternatives to RLS

If RLS doesn’t fit your needs, consider using other PostgreSQL features like Views or Table Partitioning for achieving similar results.