Fixes #30555 - Authorizer uses subselect for joined_on

[ezr-ondrej]

if we use joined_on class, we are using the where clause on that class through the association.
This is very volatile and it doesnt play well with the Host STI.

See the test file for example failure

The original idea for the fix came from @sufanek1, kudos! 👍

[theforeman-bot]

Issues: #30555

[ShimShtein]

I suppose it's better than failing, but can you share an explain plan for such query? I think it can get quite resource - intensive on the DB side. Especially when the sub-select is quite big.

[ShimShtein]

Shouldn't we modify the SELECT part of the subquery to return only the assoc.primary_key column?

[ezr-ondrej]

Rails does that automatically if you pass scope to the id field.

[ezr-ondrej]

The test builds following query

SELECT "fact_values".* FROM "fact_values" INNER JOIN "hosts" ON "hosts"."id" = "fact_values"."host_id" WHERE "fact_values"."host_id" IN (SELECT "hosts"."id" FROM "hosts" INNER JOIN "operatingsystems" ON "operatingsystems"."id" = "hosts"."operatingsystem_id" WHERE "hosts"."type" = 'Host::Managed' AND (("operatingsystems"."name" = 'Debian')))

Which have the following plan

EXPLAIN for: SELECT "fact_values".* FROM "fact_values" INNER JOIN "hosts" ON "hosts"."id" = "fact_values"."host_id" WHERE "fact_values"."host_id" IN (SELECT "hosts"."id" FROM "hosts" INNER JOIN "operatingsystems" ON "operatingsystems"."id" = "hosts"."operatingsystem_id" WHERE "hosts"."type" = 'Host::Managed' AND (("operatingsystems"."name" = 'Debian')))
                                                              QUERY PLAN
---------------------------------------------------------------------------------------------------------------------------------------
 Nested Loop  (cost=9.55..23.95 rows=440 width=64)
   ->  Nested Loop  (cost=9.40..18.89 rows=1 width=8)
         ->  HashAggregate  (cost=9.27..9.28 rows=1 width=4)
               Group Key: hosts_1.id
               ->  Nested Loop  (cost=0.14..9.26 rows=1 width=4)
                     Join Filter: (hosts_1.operatingsystem_id = operatingsystems.id)
                     ->  Index Scan using index_hosts_on_type_and_organization_id_and_location_id on hosts hosts_1  (cost=0.14..8.15 rows=1 width=8)
                           Index Cond: ((type)::text = 'Host::Managed'::text)
                     ->  Seq Scan on operatingsystems  (cost=0.00..1.10 rows=1 width=4)
                           Filter: ((name)::text = 'Debian'::text)
         ->  Index Only Scan using hosts_pkey on hosts  (cost=0.14..8.15 rows=1 width=4)
               Index Cond: (id = hosts_1.id)
   ->  Index Scan using index_fact_values_on_host_id on fact_values  (cost=0.15..5.02 rows=4 width=64)
         Index Cond: (host_id = hosts.id)

I'm not sure if the subquery is efficient or not, although the data throughput should be higher as we don't pull the additional joined data. The rest should be more or less the same, but depends on the optimizer 🤷

[ezr-ondrej]

@ShimShtein any other issues? :)
Or would you like to go over it together?

[ezr-ondrej]

includes here doesn't work as if used in subselect, it does select only id and Rails then considers the join useless, as includes primary intention was to preload. Thus I had to go with left_outer_joins here.

[ezr-ondrej]

@ShimShtein #7913 should fix the issue you've hitted in your setup, could you try these together to see if it really helps?

[ShimShtein]

ACK, works as expected! And #7913 indeed helped with my setup.

Thanks @ezr-ondrej!