Replace Group ancestors scope with linear version

What does this MR do and why?

In this MR, we're switching the behavior of the method Group#ids_with_disabled_email to use the linear version. The new behavior is behind the linear_group_ancestor_scopes feature flag.

Database changes

In these examples, we're passing 6k groups to the query to test it with heavy data.

The old query was:

SELECT "id"
FROM
  (SELECT *
   FROM namespaces) AS namespaces_with_emails_disabled
WHERE "namespaces_with_emails_disabled"."id" IN
    (SELECT "namespaces"."id"
     FROM "namespaces"
     INNER JOIN "members" ON "namespaces"."id" = "members"."source_id"
     WHERE "members"."type" = 'GroupMember'
       AND "members"."source_type" = 'Namespace'
       AND "namespaces"."type" = 'Group'
       AND "members"."user_id" = 1614863
       AND "members"."requested_at" IS NULL
       AND (access_level >= 10))
  AND (EXISTS
         (WITH RECURSIVE "base_and_ancestors" AS (
                                                    (SELECT "namespaces".*
                                                     FROM "namespaces"
                                                     WHERE "namespaces"."type" = 'Group'
                                                       AND (id = namespaces_with_emails_disabled.id))
                                                  UNION
                                                    (SELECT "namespaces".*
                                                     FROM "namespaces",
                                                          "base_and_ancestors"
                                                     WHERE "namespaces"."type" = 'Group'
                                                       AND "namespaces"."id" = "base_and_ancestors"."parent_id")) SELECT 1
          FROM "base_and_ancestors" AS "namespaces"
          WHERE "namespaces"."emails_disabled" = TRUE
          LIMIT 1))

This is the query plan and the execution times:

Time: 208.663 ms
  - planning: 1.798 ms
  - execution: 206.865 ms
    - I/O read: 0.000 ms
    - I/O write: 0.000 ms

Shared buffers:
  - hits: 90505 (~707.10 MiB) from the buffer pool
  - reads: 0 from the OS file cache, including disk I/O
  - dirtied: 0
  - writes: 0

The new query is:

SELECT "id"
FROM
  (SELECT *
   FROM namespaces) AS namespaces_with_emails_disabled
WHERE "namespaces_with_emails_disabled"."id" IN
    (SELECT "namespaces"."id"
     FROM "namespaces"
     INNER JOIN "members" ON "namespaces"."id" = "members"."source_id"
     WHERE "members"."type" = 'GroupMember'
       AND "members"."source_type" = 'Namespace'
       AND "namespaces"."type" = 'Group'
       AND "members"."user_id" = 1614863
       AND "members"."requested_at" IS NULL
       AND (access_level >= 10))
  AND (EXISTS
         (SELECT 1
          FROM
            (SELECT "namespaces".*
             FROM "namespaces"
             WHERE "namespaces"."id" IN
                 (SELECT unnest(traversal_ids)
                  FROM "namespaces"
                  WHERE (id = namespaces_with_emails_disabled.id))) namespaces
          WHERE "namespaces"."emails_disabled" = TRUE
          LIMIT 1))

This is the query plan and the execution times:

Time: 117.777 ms
  - planning: 1.419 ms
  - execution: 116.358 ms
    - I/O read: 0.000 ms
    - I/O write: 0.000 ms

Shared buffers:
  - hits: 115075 (~899.00 MiB) from the buffer pool
  - reads: 0 from the OS file cache, including disk I/O
  - dirtied: 0
  - writes: 0

How to set up and validate locally

Example below:

1. Enable the feature flag for linear scopes

   Feature.enable(:use_traversal_ids)

2. Enable the feature flag for linear ancestors scopes

   Feature.enable(:use_traversal_ids_for_ancestor_scopes)

3. Enable the feature flag for Ci::Runner linear ancestors scopes

   Feature.enable(:linear_group_ancestor_scopes)

4. Execute the following in the Rails console with the proper id depending on the scope testing:

Group.ids_with_disabled_email(User.first.groups)

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #339194 (closed)

app/models/group.rb

@@ -192,9 +192,15 @@ def preset_root_ancestor_for(groups)
     # Returns the ids of the passed group models where the `emails_disabled`
     # column is set to true anywhere in the ancestor hierarchy.
     def ids_with_disabled_email(groups)
-      innner_query = Gitlab::ObjectHierarchy
-        .new(Group.where('id = namespaces_with_emails_disabled.id'))
-        .base_and_ancestors
+      inner_groups = Group.where('id = namespaces_with_emails_disabled.id')
+
+      inner_ancestors = if Feature.enabled?(:linear_group_ancestor_scopes, default_enabled: :yaml)
+                          inner_groups.self_and_ancestors
+                        else
+                          Gitlab::ObjectHierarchy.new(inner_groups).base_and_ancestors
+                        end
+
+      inner_query = inner_ancestors
         .where(emails_disabled: true)
         .select('1')
         .limit(1)
@@ -202,7 +208,7 @@ def ids_with_disabled_email(groups)
       group_ids = Namespace
         .from('(SELECT * FROM namespaces) as namespaces_with_emails_disabled')
         .where(namespaces_with_emails_disabled: { id: groups })
-        .where('EXISTS (?)', innner_query)
+        .where('EXISTS (?)', inner_query)
         .pluck(:id)
 
       Set.new(group_ids)