Hi,
Is there a way to visualize RLS policy check(s) in the query plan?
Regards,
Akash Anand
On Mon, Jul 10, 2023 at 11:33 AM Akash Anand wrote:
> 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, 1000) 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
>
>
