Re: Partition pruning with array-contains check and current_setting function - Mailing list pgsql-performance

Hello all. I am trying to make postgres 16 prune partition for queries with `WHERE tenant_id=ANY(current_setting('my.tenant_id')::integer[])`, but I haven't been able to make it work, and naturally it impacts performance so I thought this list would be appropriate.

Here's the SQL I tried (but feel free to skip to the end as I'm sure all this stuff is obvious to you!):

CREATE TABLE tbl (id SERIAL NOT NULL, tenant_id INT NOT NULL, some_col INT, PRIMARY KEY (tenant_id, id))
PARTITION BY HASH (tenant_id);

CREATE TABLE tbl1 PARTITION OF tbl FOR VALUES WITH (MODULUS 2, REMAINDER 0);
CREATE TABLE tbl2 PARTITION OF tbl FOR VALUES WITH (MODULUS 2, REMAINDER 1);

INSERT INTO tbl (tenant_id, some_col) SELECT 1, * FROM generate_series(1,10000);
INSERT INTO tbl (tenant_id, some_col) SELECT 3, * FROM generate_series(1,10000);

Partition pruning works as expected for this query (still not an array-contains check):
EXPLAIN ANALYZE SELECT COUNT(*) FROM tbl WHERE tenant_id=1;

When reading from a setting it also prunes partitions correctly:
SET my.tenant_id=1;
EXPLAIN ANALYZE SELECT COUNT(*) FROM tbl WHERE tenant_id=current_setting('my.tenant_id')::integer;

It still does partition pruning if we use a scalar subquery. I can see the (never executed) scans in the plan.
EXPLAIN ANALYZE SELECT COUNT(*) FROM tbl WHERE tenant_id=(SELECT current_setting('my.tenant_id')::integer);

But how about an array-contains check? Still prunes, which is nice.
EXPLAIN ANALYZE SELECT COUNT(*) FROM tbl WHERE tenant_id=ANY('{1}'::integer[]);

However, it doesn't prune if the array is in a setting:
SET my.tenant_id='{1}';
EXPLAIN ANALYZE SELECT COUNT(*) FROM tbl WHERE tenant_id=ANY(current_setting('my.tenant_id')::integer[]);

I actually expected that when in a setting, none of the previous queries would've done partition pruning because I thought `current_setting` is not a stable function. But some of them did, which surprised me.

So I thought maybe if I put it in a scalar query it will give me an InitPlan node, but it looks like method resolution for =ANY won't let me try this:

EXPLAIN ANALYZE SELECT COUNT(*) FROM tbl WHERE tenant_id=ANY((SELECT current_setting('my.tenant_id')::integer[]));

ERROR:  operator does not exist: integer = integer[]

I tried using UNNEST, but that adds a Hash Semi Join to the plan which also doesn't do partition pruning.
EXPLAIN ANALYZE SELECT COUNT(*) FROM tbl WHERE tenant_id=ANY((SELECT UNNEST(current_setting('my.tenant_id')::integer[])));

My question is if there's a way to do partition pruning based on array-contains operator if the array is in a setting. The use-case is to make Row Level Security policies do partition pruning "automatically" in a setting where users can be in more than one tenant.

It feels like this would work if there were a non-overloaded operator that takes in an array and a single element and tests for array-contains, because then I could use that operator with a scalar subquery and get an InitPlan node. But I'm new to all of this, so apologies if I'm getting it all wrong!

Thanks in advance,
Marcelo.