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.

6 files changed, 42 insertions, 121 deletions

diff --git a/app/models/concerns/routable.rb b/app/models/concerns/routable.rb
index c4463abdfe6..63d02b76f6b 100644
--- a/app/models/concerns/routable.rb
+++ b/app/models/concerns/routable.rb
@@ -84,89 +84,6 @@ module Routable
         joins(:route).where(wheres.join(' OR '))
       end
     end
-
-    # Builds a relation to find multiple objects that are nested under user membership
-    #
-    # Usage:
-    #
-    #     Klass.member_descendants(1)
-    #
-    # Returns an ActiveRecord::Relation.
-    def member_descendants(user_id)
-      joins(:route).
-        joins("INNER JOIN routes r2 ON routes.path LIKE CONCAT(r2.path, '/%')
-               INNER JOIN members ON members.source_id = r2.source_id
-               AND members.source_type = r2.source_type").
-        where('members.user_id = ?', user_id)
-    end
-
-    # Builds a relation to find multiple objects that are nested under user
-    # membership. Includes the parent, as opposed to `#member_descendants`
-    # which only includes the descendants.
-    #
-    # Usage:
-    #
-    #     Klass.member_self_and_descendants(1)
-    #
-    # Returns an ActiveRecord::Relation.
-    def member_self_and_descendants(user_id)
-      joins(:route).
-        joins("INNER JOIN routes r2 ON routes.path LIKE CONCAT(r2.path, '/%')
-               OR routes.path = r2.path
-               INNER JOIN members ON members.source_id = r2.source_id
-               AND members.source_type = r2.source_type").
-        where('members.user_id = ?', user_id)
-    end
-
-    # Returns all objects in a hierarchy, where any node in the hierarchy is
-    # under the user membership.
-    #
-    # Usage:
-    #
-    #     Klass.member_hierarchy(1)
-    #
-    # Examples:
-    #
-    #     Given the following group tree...
-    #
-    #            _______group_1_______
-    #           |                     |
-    #           |                     |
-    #     nested_group_1        nested_group_2
-    #           |                     |
-    #           |                     |
-    #     nested_group_1_1      nested_group_2_1
-    #
-    #
-    #     ... the following results are returned:
-    #
-    #     * the user is a member of group 1
-    #       => 'group_1',
-    #          'nested_group_1', nested_group_1_1',
-    #          'nested_group_2', 'nested_group_2_1'
-    #
-    #     * the user is a member of nested_group_2
-    #       => 'group1',
-    #          'nested_group_2', 'nested_group_2_1'
-    #
-    #     * the user is a member of nested_group_2_1
-    #       => 'group1',
-    #          'nested_group_2', 'nested_group_2_1'
-    #
-    # Returns an ActiveRecord::Relation.
-    def member_hierarchy(user_id)
-      paths = member_self_and_descendants(user_id).pluck('routes.path')
-
-      return none if paths.empty?
-
-      wheres = paths.map do |path|
-        "#{connection.quote(path)} = routes.path
-         OR
-         #{connection.quote(path)} LIKE CONCAT(routes.path, '/%')"
-      end
-
-      joins(:route).where(wheres.join(' OR '))
-    end
   end
 
   def full_name
diff --git a/app/models/concerns/select_for_project_authorization.rb b/app/models/concerns/select_for_project_authorization.rb
index 50a1d7fc3e1..58194b0ea13 100644
--- a/app/models/concerns/select_for_project_authorization.rb
+++ b/app/models/concerns/select_for_project_authorization.rb
@@ -3,7 +3,11 @@ module SelectForProjectAuthorization
 
   module ClassMethods
     def select_for_project_authorization
-      select("members.user_id, projects.id AS project_id, members.access_level")
+      select("projects.id AS project_id, members.access_level")
+    end
+
+    def select_as_master_for_project_authorization
+      select(["projects.id AS project_id", "#{Gitlab::Access::MASTER} AS access_level"])
     end
   end
 end
diff --git a/app/models/group.rb b/app/models/group.rb
index 6aab477f431..be944da5a67 100644
--- a/app/models/group.rb
+++ b/app/models/group.rb
@@ -38,6 +38,10 @@ class Group < Namespace
   after_save :update_two_factor_requirement
 
   class << self
+    def supports_nested_groups?
+      Gitlab::Database.postgresql?
+    end
+
     # Searches for groups matching the given query.
     #
     # This method uses ILIKE on PostgreSQL and LIKE on MySQL.
@@ -78,7 +82,7 @@ class Group < Namespace
       if current_scope.joins_values.include?(:shared_projects)
         joins('INNER JOIN namespaces project_namespace ON project_namespace.id = projects.namespace_id')
           .where('project_namespace.share_with_group_lock = ?',  false)
-          .select("members.user_id, projects.id AS project_id, LEAST(project_group_links.group_access, members.access_level) AS access_level")
+          .select("projects.id AS project_id, LEAST(project_group_links.group_access, members.access_level) AS access_level")
       else
         super
       end
diff --git a/app/models/namespace.rb b/app/models/namespace.rb
index a7ede5e3b9e..985395a6fe2 100644
--- a/app/models/namespace.rb
+++ b/app/models/namespace.rb
@@ -176,26 +176,22 @@ class Namespace < ActiveRecord::Base
     projects.with_shared_runners.any?
   end
 
-  # Scopes the model on ancestors of the record
+  # Returns all the ancestors of the current namespaces.
   def ancestors
-    if parent_id
-      path = route ? route.path : full_path
-      paths = []
+    return self.class.none if !Group.supports_nested_groups? || !parent_id
 
-      until path.blank?
-        path = path.rpartition('/').first
-        paths << path
-      end
-
-      self.class.joins(:route).where('routes.path IN (?)', paths).reorder('routes.path ASC')
-    else
-      self.class.none
-    end
+    Gitlab::GroupHierarchy.
+      new(self.class.where(id: parent_id)).
+      base_and_ancestors
   end
 
-  # Scopes the model on direct and indirect children of the record
+  # Returns all the descendants of the current namespace.
   def descendants
-    self.class.joins(:route).merge(Route.inside_path(route.path)).reorder('routes.path ASC')
+    return self.class.none unless Group.supports_nested_groups?
+
+    Gitlab::GroupHierarchy.
+      new(self.class.where(parent_id: id)).
+      base_and_descendants
   end
 
   def user_ids_for_project_authorizations
diff --git a/app/models/project_authorization.rb b/app/models/project_authorization.rb
index 4c7f4f5a429..def09675253 100644
--- a/app/models/project_authorization.rb
+++ b/app/models/project_authorization.rb
@@ -6,6 +6,12 @@ class ProjectAuthorization < ActiveRecord::Base
   validates :access_level, inclusion: { in: Gitlab::Access.all_values }, presence: true
   validates :user, uniqueness: { scope: [:project, :access_level] }, presence: true
 
+  def self.select_from_union(union)
+    select(['project_id', 'MAX(access_level) AS access_level']).
+      from("(#{union.to_sql}) #{ProjectAuthorization.table_name}").
+      group(:project_id)
+  end
+
   def self.insert_authorizations(rows, per_batch = 1000)
     rows.each_slice(per_batch) do |slice|
       tuples = slice.map do |tuple|
diff --git a/app/models/user.rb b/app/models/user.rb
index c7160a6af14..2cf995f8c31 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -10,9 +10,12 @@ class User < ActiveRecord::Base
   include Sortable
   include CaseSensitivity
   include TokenAuthenticatable
+  include IgnorableColumn
 
   DEFAULT_NOTIFICATION_LEVEL = :participating
 
+  ignore_column :authorized_projects_populated
+
   add_authentication_token_field :authentication_token
   add_authentication_token_field :incoming_email_token
 
@@ -212,7 +215,6 @@ class User < ActiveRecord::Base
   scope :blocked, -> { with_states(:blocked, :ldap_blocked) }
   scope :external, -> { where(external: true) }
   scope :active, -> { with_state(:active).non_internal }
-  scope :not_in_project, ->(project) { project.users.present? ? where("id not in (:ids)", ids: project.users.map(&:id) ) : all }
   scope :without_projects, -> { where('id NOT IN (SELECT DISTINCT(user_id) FROM members WHERE user_id IS NOT NULL AND requested_at IS NULL)') }
   scope :todo_authors, ->(user_id, state) { where(id: Todo.where(user_id: user_id, state: state).select(:author_id)) }
   scope :order_recent_sign_in, -> { reorder(Gitlab::Database.nulls_last_order('last_sign_in_at', 'DESC')) }
@@ -504,23 +506,18 @@ class User < ActiveRecord::Base
     Group.where("namespaces.id IN (#{union.to_sql})")
   end
 
-  def nested_groups
-    Group.member_descendants(id)
-  end
-
+  # Returns a relation of groups the user has access to, including their parent
+  # and child groups (recursively).
   def all_expanded_groups
-    Group.member_hierarchy(id)
+    return groups unless Group.supports_nested_groups?
+
+    Gitlab::GroupHierarchy.new(groups).all_groups
   end
 
   def expanded_groups_requiring_two_factor_authentication
     all_expanded_groups.where(require_two_factor_authentication: true)
   end
 
-  def nested_groups_projects
-    Project.joins(:namespace).where('namespaces.parent_id IS NOT NULL').
-      member_descendants(id)
-  end
-
   def refresh_authorized_projects
     Users::RefreshAuthorizedProjectsService.new(self).execute
   end
@@ -529,18 +526,15 @@ class User < ActiveRecord::Base
     project_authorizations.where(project_id: project_ids).delete_all
   end
 
-  def set_authorized_projects_column
-    unless authorized_projects_populated
-      update_column(:authorized_projects_populated, true)
-    end
-  end
-
   def authorized_projects(min_access_level = nil)
-    refresh_authorized_projects unless authorized_projects_populated
-
-    # We're overriding an association, so explicitly call super with no arguments or it would be passed as `force_reload` to the association
+    # We're overriding an association, so explicitly call super with no
+    # arguments or it would be passed as `force_reload` to the association
     projects = super()
-    projects = projects.where('project_authorizations.access_level >= ?', min_access_level) if min_access_level
+
+    if min_access_level
+      projects = projects.
+        where('project_authorizations.access_level >= ?', min_access_level)
+    end
 
     projects
   end