Why is query performance on RLS enabled Postgres worse?

From: Akash Anand <akash(at)hasura(dot)io>
To: pgsql-performance(at)lists(dot)postgresql(dot)org
Subject: Why is query performance on RLS enabled Postgres worse?
Date: 2023-07-10 06:03:47
Message-ID: CAPcM0QW3yFGqnRGvR2PzbeZVYBuQTkE72+rdt9dE6Bqs2KSwgQ@mail.gmail.com
Views: Raw Message | Whole Thread | Download mbox | Resend email
Thread:
Lists: pgsql-performance

Hi,

------
Postgres version
------
postgres=# SELECT version();
version

-----------------------------------------------------------------------------------------------------------------------------------
PostgreSQL 15.3 (Debian 15.3-1.pgdg110+1) on aarch64-unknown-linux-gnu,
compiled by gcc (Debian 10.2.1-6) 10.2.1 20210110, 64-bit
(1 row)
------

------
Load data
------
Chinook database
https://github.com/lerocha/chinook-database/blob/master/ChinookDatabase/DataSources/Chinook_PostgreSql.sql
------

------
Insert dummy data into Track to bring rows count to 10 million
------
INSERT INTO "Track"("TrackId", "Name", "AlbumId", "MediaTypeId", "GenreId",
"Milliseconds", "Bytes", "UnitPrice")
SELECT i::int, i::text, 1, 1, 1, 276349, 9056902, 0.99
FROM generate_series(3504, 10000000) AS t(i);
------

------
Setup role and policies
------
create role "User";
grant select on "Album" to "User";
CREATE POLICY artist_rls_policy ON "Album" FOR SELECT TO public USING
("ArtistId"=((current_setting('rls.artistID'))::integer));
ALTER TABLE "Album" ENABLE ROW LEVEL SECURITY;
grant select on "Track" to "User";
CREATE POLICY album_rls_policy ON "Track" FOR SELECT to public
USING (
EXISTS (
select 1 from "Album" where "Track"."AlbumId" = "Album"."AlbumId"
)
);
ALTER TABLE "Track" ENABLE ROW LEVEL SECURITY;
------

------
Query and verify the policies through psql
------
set role "User";
set rls.artistID = '116';
select * from "Track";
------

------
Query plan for postgres
------
postgres=> explain analyze select * from "Track";
QUERY PLAN

-------------------------------------------------------------------------------------------------------------------------------------
Seq Scan on "Track" (cost=0.00..34589179.11 rows=2110303 width=58)
(actual time=68.097..350.074 rows=14 loops=1)
Filter: (hashed SubPlan 2)
Rows Removed by Filter: 4220538
SubPlan 2
-> Index Scan using "IFK_AlbumArtistId" on "Album" (cost=0.15..8.17
rows=1 width=4) (actual time=0.017..0.018 rows=1 loops=1)
Index Cond: ("ArtistId" =
(current_setting('rls.artistID'::text))::integer)
Planning Time: 0.091 ms
JIT:
Functions: 17
Options: Inlining true, Optimization true, Expressions true, Deforming
true
Timing: Generation 1.008 ms, Inlining 11.450 ms, Optimization 33.233 ms,
Emission 22.443 ms, Total 68.135 ms
Execution Time: 350.922 ms
(12 rows)
------

------
Disabled ROW LEVEL SECURITY and get appropriate tracks
------

QUERY PLAN

--------------------------------------------------------------------------------------------------------------------------------------------------------------
Aggregate (cost=7657.40..7657.41 rows=1 width=32) (actual
time=0.070..0.071 rows=1 loops=1)
-> Nested Loop Left Join (cost=7650.01..7657.38 rows=1 width=55)
(actual time=0.061..0.068 rows=1 loops=1)
-> Seq Scan on "Album" (cost=0.00..7.34 rows=1 width=27) (actual
time=0.020..0.026 rows=1 loops=1)
Filter: ("ArtistId" = 116)
Rows Removed by Filter: 346
-> Aggregate (cost=7650.01..7650.02 rows=1 width=32) (actual
time=0.040..0.040 rows=1 loops=1)
-> Nested Loop (cost=0.43..6107.07 rows=102863 width=11)
(actual time=0.016..0.026 rows=14 loops=1)
-> Seq Scan on "Album" "__be_0_Album"
(cost=0.00..8.21 rows=1 width=4) (actual time=0.008..0.015 rows=1 loops=1)
Filter: (("AlbumId" = "Album"."AlbumId") AND
("ArtistId" = 116))
Rows Removed by Filter: 346
-> Index Scan using "IFK_TrackAlbumId" on "Track"
(cost=0.43..5070.23 rows=102863 width=15) (actual time=0.008..0.009
rows=14 loops=1)
Index Cond: ("AlbumId" = "Album"."AlbumId")
SubPlan 2
-> Result (cost=0.00..0.01 rows=1 width=32) (actual
time=0.000..0.000 rows=1 loops=14)
SubPlan 1
-> Result (cost=0.00..0.01 rows=1 width=32) (actual
time=0.000..0.000 rows=1 loops=1)
Planning Time: 0.182 ms
Execution Time: 0.094 ms
(18 rows)
------

Why did Postgres choose to do a sequential scan on Track when RLS is
enabled?

Regards,
Akash Anand

Responses

Browse pgsql-performance by date

  From Date Subject
Next Message Akash Anand 2023-07-10 07:01:00 Re: Why is query performance on RLS enabled Postgres worse?
Previous Message Jeff Janes 2023-06-27 12:47:44 Re: Helping planner to chose sequential scan when it improves performance