Use CTEs for nested groups and authorizations

This commit introduces the usage of Common Table Expressions (CTEs) to
efficiently retrieve nested group hierarchies, without having to rely on
the "routes" table (which is an _incredibly_ inefficient way of getting
the data). This requires a patch to ActiveRecord (found in the added
initializer) to work properly as ActiveRecord doesn't support WITH
statements properly out of the box.

Unfortunately MySQL provides no efficient way of getting nested groups.
For example, the old routes setup could easily take 5-10 seconds
depending on the amount of "routes" in a database. Providing vastly
different logic for both MySQL and PostgreSQL will negatively impact the
development process. Because of this the various nested groups related
methods return empty relations when used in combination with MySQL.

For project authorizations the logic is split up into two classes:

* Gitlab::ProjectAuthorizations::WithNestedGroups
* Gitlab::ProjectAuthorizations::WithoutNestedGroups

Both classes get the fresh project authorizations (= as they should be
in the "project_authorizations" table), including nested groups if
PostgreSQL is used. The logic of these two classes is quite different
apart from their public interface. This complicates development a bit,
but unfortunately there is no way around this.

This commit also introduces Gitlab::GroupHierarchy. This class can be
used to get the ancestors and descendants of a base relation, or both by
using a UNION. This in turn is used by methods such as:

* Namespace#ancestors
* Namespace#descendants
* User#all_expanded_groups

Again this class relies on CTEs and thus only works on PostgreSQL. The
Namespace methods will return an empty relation when MySQL is used,
while User#all_expanded_groups will return only the groups a user is a
direct member of.

Performance wise the impact is quite large. For example, on GitLab.com
Namespace#descendants used to take around 580 ms to retrieve data for a
particular user. Using CTEs we are able to reduce this down to roughly 1
millisecond, returning the exact same data.

== On The Fly Refreshing

Refreshing of authorizations on the fly (= when
users.authorized_projects_populated was not set) is removed with this
commit. This simplifies the code, and ensures any queries used for
authorizations are not mutated because they are executed in a Rails
scope (e.g. Project.visible_to_user).

This commit includes a migration to schedule refreshing authorizations
for all users, ensuring all of them have their authorizations in place.
Said migration schedules users in batches of 5000, with 5 minutes
between every batch to smear the load around a bit.

== Spec Changes

This commit also introduces some changes to various specs. For example,
some specs for ProjectTeam assumed that creating a personal project
would _not_ lead to the owner having access, which is incorrect. Because
we also no longer refresh authorizations on the fly for new users some
code had to be added to the "empty_project" factory. This chunk of code
ensures that the owner's permissions are refreshed after creating the
project, something that is normally done in Projects::CreateService.

1 files changed, 17 insertions, 49 deletions

diff --git a/spec/services/users/refresh_authorized_projects_service_spec.rb b/spec/services/users/refresh_authorized_projects_service_spec.rb
index b19374ef1a2..8c40d25e00c 100644
--- a/spec/services/users/refresh_authorized_projects_service_spec.rb
+++ b/spec/services/users/refresh_authorized_projects_service_spec.rb
@@ -1,15 +1,13 @@
 require 'spec_helper'
 
 describe Users::RefreshAuthorizedProjectsService do
-  let(:project) { create(:empty_project) }
+  # We're using let! here so that any expectations for the service class are not
+  # triggered twice.
+  let!(:project) { create(:empty_project) }
+
   let(:user) { project.namespace.owner }
   let(:service) { described_class.new(user) }
 
-  def create_authorization(project, user, access_level = Gitlab::Access::MASTER)
-    ProjectAuthorization.
-      create!(project: project, user: user, access_level: access_level)
-  end
-
   describe '#execute', :redis do
     it 'refreshes the authorizations using a lease' do
       expect_any_instance_of(Gitlab::ExclusiveLease).to receive(:try_obtain).
@@ -31,7 +29,8 @@ describe Users::RefreshAuthorizedProjectsService do
 
     it 'updates the authorized projects of the user' do
       project2 = create(:empty_project)
-      to_remove = create_authorization(project2, user)
+      to_remove = user.project_authorizations.
+        create!(project: project2, access_level: Gitlab::Access::MASTER)
 
       expect(service).to receive(:update_authorizations).
         with([to_remove.project_id], [[user.id, project.id, Gitlab::Access::MASTER]])
@@ -40,7 +39,10 @@ describe Users::RefreshAuthorizedProjectsService do
     end
 
     it 'sets the access level of a project to the highest available level' do
-      to_remove = create_authorization(project, user, Gitlab::Access::DEVELOPER)
+      user.project_authorizations.delete_all
+
+      to_remove = user.project_authorizations.
+        create!(project: project, access_level: Gitlab::Access::DEVELOPER)
 
       expect(service).to receive(:update_authorizations).
         with([to_remove.project_id], [[user.id, project.id, Gitlab::Access::MASTER]])
@@ -61,34 +63,10 @@ describe Users::RefreshAuthorizedProjectsService do
 
         service.update_authorizations([], [])
       end
-
-      context 'when the authorized projects column is not set' do
-        before do
-          user.update!(authorized_projects_populated: nil)
-        end
-
-        it 'populates the authorized projects column' do
-          service.update_authorizations([], [])
-
-          expect(user.authorized_projects_populated).to eq true
-        end
-      end
-
-      context 'when the authorized projects column is set' do
-        before do
-          user.update!(authorized_projects_populated: true)
-        end
-
-        it 'does nothing' do
-          expect(user).not_to receive(:set_authorized_projects_column)
-
-          service.update_authorizations([], [])
-        end
-      end
     end
 
     it 'removes authorizations that should be removed' do
-      authorization = create_authorization(project, user)
+      authorization = user.project_authorizations.find_by(project_id: project.id)
 
       service.update_authorizations([authorization.project_id])
 
@@ -96,6 +74,8 @@ describe Users::RefreshAuthorizedProjectsService do
     end
 
     it 'inserts authorizations that should be added' do
+      user.project_authorizations.delete_all
+
       service.update_authorizations([], [[user.id, project.id, Gitlab::Access::MASTER]])
 
       authorizations = user.project_authorizations
@@ -105,16 +85,6 @@ describe Users::RefreshAuthorizedProjectsService do
       expect(authorizations[0].project_id).to eq(project.id)
       expect(authorizations[0].access_level).to eq(Gitlab::Access::MASTER)
     end
-
-    it 'populates the authorized projects column' do
-      # make sure we start with a nil value no matter what the default in the
-      # factory may be.
-      user.update!(authorized_projects_populated: nil)
-
-      service.update_authorizations([], [[user.id, project.id, Gitlab::Access::MASTER]])
-
-      expect(user.authorized_projects_populated).to eq(true)
-    end
   end
 
   describe '#fresh_access_levels_per_project' do
@@ -163,7 +133,7 @@ describe Users::RefreshAuthorizedProjectsService do
       end
     end
 
-    context 'projects of subgroups of groups the user is a member of' do
+    context 'projects of subgroups of groups the user is a member of', :nested_groups do
       let(:group) { create(:group) }
       let(:nested_group) { create(:group, parent: group) }
       let!(:other_project) { create(:empty_project, group: nested_group) }
@@ -191,7 +161,7 @@ describe Users::RefreshAuthorizedProjectsService do
       end
     end
 
-    context 'projects shared with subgroups of groups the user is a member of' do
+    context 'projects shared with subgroups of groups the user is a member of', :nested_groups do
       let(:group) { create(:group) }
       let(:nested_group) { create(:group, parent: group) }
       let(:other_project) { create(:empty_project) }
@@ -208,8 +178,6 @@ describe Users::RefreshAuthorizedProjectsService do
   end
 
   describe '#current_authorizations_per_project' do
-    before { create_authorization(project, user) }
-
     let(:hash) { service.current_authorizations_per_project }
 
     it 'returns a Hash' do
@@ -233,13 +201,13 @@ describe Users::RefreshAuthorizedProjectsService do
   describe '#current_authorizations' do
     context 'without authorizations' do
       it 'returns an empty list' do
+        user.project_authorizations.delete_all
+
         expect(service.current_authorizations.empty?).to eq(true)
       end
     end
 
     context 'with an authorization' do
-      before { create_authorization(project, user) }
-
       let(:row) { service.current_authorizations.take }
 
       it 'returns the currently authorized projects' do