RLS Inaccurate Limit/Offset Results In PostgreSQL

Nov 12, 2025 by Alex Johnson 50 views

RLS Creates Inaccurate Limit and Offset Results in BharatDBPG, BharatDBMS-PG

Introduction

This article addresses a potential issue where Row Level Security (RLS) in PostgreSQL, specifically within BharatDBPG and BharatDBMS-PG, can lead to inaccurate results when using LIMIT and OFFSET clauses. This problem arises when an explicit ORDER BY clause is not included in the query. The inconsistency can be particularly problematic in applications where data pagination or selective retrieval is essential. Let’s dive deeper into the details and understand how to mitigate this issue.

The core issue revolves around how PostgreSQL optimizes queries that involve RLS, LIMIT, and OFFSET. Without a defined order, the database might return rows in an unpredictable sequence. When RLS is applied, this unpredictability can be amplified, leading to unexpected or duplicate results when using LIMIT and OFFSET to paginate through data. This article provides a detailed analysis of the scenario, sample data, and potential solutions to ensure data integrity and consistent query behavior in your PostgreSQL databases. By understanding the nuances of this interaction, developers and database administrators can implement strategies to avoid these pitfalls and maintain reliable data retrieval.

Furthermore, we will explore the specific conditions under which this issue manifests and examine the impact of different RLS policies on query outcomes. This includes scenarios where the RLS policy filters data based on user roles or other criteria. By understanding these scenarios, you can better assess the risk to your own applications and take proactive steps to prevent data inconsistencies. The examples provided will help illustrate the problem and offer practical guidance on how to construct queries that are both secure and accurate. By the end of this article, you will have a comprehensive understanding of how RLS interacts with LIMIT and OFFSET and how to ensure your queries return the expected results, even in complex database environments.

Problem Description

The core problem lies in the interaction between Row Level Security, the LIMIT clause, and the OFFSET clause. Without an ORDER BY clause, the order in which rows are returned from a query is not guaranteed. When RLS is enabled, the filtering applied by the RLS policy can change the order in which rows are processed by the LIMIT and OFFSET clauses, leading to inconsistent results. The original reporter, Mike Brancato, observed this behavior in PostgreSQL 17.6.

To illustrate, consider a scenario where a user with RLS enabled attempts to retrieve a subset of rows from a table using LIMIT and OFFSET. Without RLS, the LIMIT and OFFSET clauses would typically return a consistent set of rows. However, with RLS in place, the RLS policy filters the rows before the LIMIT and OFFSET clauses are applied. If the order of the rows is not deterministic (i.e., no ORDER BY clause), the filtered rows might be returned in a different order each time the query is executed, leading to different results for the same LIMIT and OFFSET values. This can cause significant issues in applications that rely on pagination or consistent data retrieval.

The impact of this issue is particularly pronounced in applications where data integrity is critical. For example, if a user is browsing a list of items and uses pagination to navigate through the list, inconsistent results can lead to items being skipped or duplicated. This can create a poor user experience and, in some cases, lead to data loss or corruption. Therefore, it is essential to understand the underlying cause of this issue and implement appropriate solutions to ensure data consistency and reliability. The subsequent sections will provide more detailed examples and potential solutions to address this problem.

Sample Data and RLS Policy

To reproduce the issue, the following sample data and RLS policy can be used:

CREATE TABLE IF NOT EXISTS "organization"
(
 "id" UUID DEFAULT gen_random_uuid(),
 "name" TEXT NOT NULL,
 "created_at" TIMESTAMPTZ NOT NULL DEFAULT NOW(),
 PRIMARY KEY ("id")
);

COPY public.organization (id, name, created_at) FROM stdin;
db8d12e7-faac-4b6a-a4f1-127c1da8b297 Test 2025-11-11 15:57:29.323547+00
11111111-1111-1111-1111-111111111111 Acme Corporation 2025-11-11 15:57:29.324394+00
22222222-2222-2222-2222-222222222222 Beta Industries 2025-11-11 15:57:29.325026+00
33333333-3333-3333-3333-333333333333 Gamma Labs 2025-11-11 15:57:29.325643+00
\.

CREATE POLICY organization_isolation_policy
ON public.organization
FOR SELECT USING (
(id = ANY
(
 ARRAY [
 '11111111-1111-1111-1111-111111111111'::uuid,
 '22222222-2222-2222-2222-222222222222'::uuid,
 '33333333-3333-3333-3333-333333333333'::uuid,
 'db8d12e7-faac-4b6a-a4f1-127c1da8b297'::uuid]
)
)
);

This SQL code sets up a table named organization with columns for id, name, and created_at. It then inserts four rows of sample data into this table. Finally, it creates an RLS policy named organization_isolation_policy that restricts SELECT access to rows where the id matches one of the UUIDs specified in the array. This policy effectively limits the data that a user with this policy enabled can see.

Using the above setup, the following queries demonstrate the issue:

SELECT * FROM organization LIMIT 1;
SELECT * FROM organization LIMIT 1 OFFSET 0;
SELECT * FROM organization LIMIT 1 OFFSET 1;

As reported, the last two queries (LIMIT 1 OFFSET 0 and LIMIT 1 OFFSET 1) return the same result, which is unexpected. This demonstrates that the OFFSET is not working as intended when RLS is enabled and there is no ORDER BY clause. This behavior highlights the importance of including an ORDER BY clause to ensure consistent and predictable results when using LIMIT and OFFSET in conjunction with RLS. The following sections will discuss potential solutions to this problem.

Analysis of the Issue

When RLS is enabled, PostgreSQL applies the RLS policy before applying the LIMIT and OFFSET clauses. Without an ORDER BY clause, the order in which rows are processed is not guaranteed. This means that the RLS policy might filter the rows in a different order each time the query is executed, leading to different results for the same LIMIT and OFFSET values.

Consider the following scenario: A user with RLS enabled queries the organization table with LIMIT 1 OFFSET 1. The RLS policy filters the rows, and the filtered rows are then processed by the LIMIT and OFFSET clauses. If the order of the filtered rows is different each time the query is executed, the OFFSET might skip a different row each time, leading to inconsistent results. This is particularly problematic when the RLS policy allows only a small subset of rows to be returned.

The key takeaway here is that the combination of RLS and the lack of a deterministic row order (due to the absence of ORDER BY) introduces unpredictability. The database engine is free to choose any execution plan that satisfies the query conditions, and this choice can vary between executions, especially when RLS is involved. This variability directly impacts the behavior of LIMIT and OFFSET, causing the observed inconsistencies. Therefore, it is crucial to enforce a specific order using ORDER BY to ensure that the results are consistent and predictable.

Solutions and Mitigations

The most straightforward solution is to always include an ORDER BY clause when using LIMIT and OFFSET, especially when RLS is enabled. The ORDER BY clause ensures that the rows are processed in a consistent order, regardless of the RLS policy.

For example, the following query will return consistent results:

SELECT * FROM organization ORDER BY created_at LIMIT 1 OFFSET 1;

By ordering the results by the created_at column, we ensure that the OFFSET will always skip the same row, leading to consistent results. It is important to choose an appropriate column for the ORDER BY clause that guarantees a stable and meaningful order for your data. This could be a primary key, a timestamp, or any other column that provides a reliable basis for sorting.

Another mitigation strategy is to review and simplify your RLS policies. Complex RLS policies can increase the likelihood of unexpected behavior. By simplifying your RLS policies, you can reduce the chances of inconsistencies and improve query performance. Ensure that your RLS policies are well-defined and thoroughly tested to avoid any unintended side effects. Regularly audit your RLS policies to ensure they are still relevant and effective.

Finally, consider using a different approach to pagination if the above solutions are not feasible. For example, you could use keyset pagination, which involves filtering the data based on the values of specific columns rather than using LIMIT and OFFSET. Keyset pagination can be more efficient and less prone to inconsistencies than traditional LIMIT and OFFSET pagination, especially in large datasets.

Conclusion

The interaction between Row Level Security, the LIMIT clause, and the OFFSET clause in PostgreSQL can lead to inaccurate results if an ORDER BY clause is not included. To avoid this issue, always include an ORDER BY clause when using LIMIT and OFFSET, especially when RLS is enabled. Additionally, review and simplify your RLS policies, and consider using a different approach to pagination if necessary. By following these guidelines, you can ensure data integrity and consistent query behavior in your PostgreSQL databases.

For more information on Row Level Security in PostgreSQL, please visit the PostgreSQL Documentation.