Do not use `restored_project`

This removes the need for `restored_project`,
but rather drops all relation caches.

It saves one SQL query per-restored top-level
object, which if you have 40k MRs,
this saves 40k SQL queries.

ee/lib/ee/gitlab/import_export/project_tree_restorer.rb

@@ -9,11 +9,9 @@ module EE
 
         private
 
-        attr_accessor :project
-
         override :remove_feature_dependent_sub_relations
         def remove_feature_dependent_sub_relations(relation_item)
-          if relation_item.is_a?(Hash) && ::Feature.disabled?(:export_designs, project, default_enabled: true)
+          if relation_item.is_a?(Hash) && ::Feature.disabled?(:export_designs, @project, default_enabled: true)
             relation_item.except!('designs', 'design_versions')
           end
         end

lib/gitlab/import_export/project_tree_restorer.rb

@@ -6,19 +6,20 @@ module Gitlab
       # Relations which cannot be saved at project level (and have a group assigned)
       GROUP_MODELS = [GroupLabel, Milestone].freeze
 
+      attr_reader :user
+      attr_reader :restored_project
+
       def initialize(user:, shared:, project:)
         @path = File.join(shared.export_path, 'project.json')
         @user = user
         @shared = shared
         @project = project
-        @project_id = project.id
         @saved = true
       end
 
       def restore
         begin
-          json = IO.read(@path)
-          @tree_hash = ActiveSupport::JSON.decode(json)
+          @tree_hash = read_tree_hash
         rescue => e
           Rails.logger.error("Import/Export error: #{e.message}") # rubocop:disable Gitlab/RailsLogger
           raise Gitlab::ImportExport::Error.new('Incorrect JSON format')
@@ -30,26 +31,32 @@ module Gitlab
 
         ActiveRecord::Base.uncached do
           ActiveRecord::Base.no_touching do
+            update_project_params
             create_relations
           end
         end
+
+        # ensure that we have latest version
+        # of the restore
+        @restored_project = @project.reload
+
+        true
       rescue => e
         @shared.error(e)
         false
       end
 
-      def restored_project
-        return @project unless @tree_hash
+      private
 
-        @restored_project ||= restore_project
+      def read_tree_hash
+        json = IO.read(@path)
+        ActiveSupport::JSON.decode(json)
       end
 
-      private
-
       def members_mapper
         @members_mapper ||= Gitlab::ImportExport::MembersMapper.new(exported_members: @project_members,
                                                                     user: @user,
-                                                                    project: restored_project)
+                                                                    project: @project)
       end
 
       # A Hash of the imported merge request ID -> imported ID.
@@ -83,13 +90,12 @@ module Gitlab
 
         remove_group_models(relation_hash) if relation_hash.is_a?(Array)
 
-        @saved = false unless restored_project.append_or_update_attribute(relation_key, relation_hash)
+        @saved = false unless @project.append_or_update_attribute(relation_key, relation_hash)
 
         save_id_mappings(relation_key, relation_hash_batch, relation_hash)
 
-        # Restore the project again, extra query that skips holding the AR objects in memory
-        @restored_project = Project.find(@project_id)
-      end
+        @project.reset
+       end
 
       # Older, serialized CI pipeline exports may only have a
       # merge_request_id and not the full hash of the merge request. To
@@ -127,12 +133,10 @@ module Gitlab
         reader.attributes_finder.find_relations_tree(:project)
       end
 
-      def restore_project
+      def update_project_params
         Gitlab::Timeless.timeless(@project) do
           @project.update(project_params)
         end
-
-        @project
       end
 
       def project_params
@@ -245,7 +249,7 @@ module Gitlab
             members_mapper: members_mapper,
             merge_requests_mapping: merge_requests_mapping,
             user: @user,
-            project: @restored_project,
+            project: @project,
             excluded_keys: excluded_keys_for_relation(relation_key))
         end.compact
 

spec/lib/gitlab/import_export/project_tree_restorer_spec.rb

@@ -520,19 +520,20 @@ describe Gitlab::ImportExport::ProjectTreeRestorer do
     end
   end
 
-  describe '#restored_project' do
+  context 'Minimal JSON' do
     let(:project) { create(:project) }
     let(:tree_hash) { { 'visibility_level' => visibility } }
     let(:restorer) { described_class.new(user: nil, shared: shared, project: project) }
 
     before do
-      restorer.instance_variable_set(:@tree_hash, tree_hash)
+      expect(restorer).to receive(:read_tree_hash) { tree_hash }
     end
 
     context 'no group visibility' do
       let(:visibility) { Gitlab::VisibilityLevel::PRIVATE }
 
       it 'uses the project visibility' do
+        expect(restorer.restore).to eq(true)
         expect(restorer.restored_project.visibility_level).to eq(visibility)
       end
     end
@@ -544,6 +545,7 @@ describe Gitlab::ImportExport::ProjectTreeRestorer do
         it 'uses private visibility' do
           stub_application_setting(restricted_visibility_levels: [Gitlab::VisibilityLevel::INTERNAL])
 
+          expect(restorer.restore).to eq(true)
           expect(restorer.restored_project.visibility_level).to eq(Gitlab::VisibilityLevel::PRIVATE)
         end
       end
@@ -561,6 +563,7 @@ describe Gitlab::ImportExport::ProjectTreeRestorer do
         let(:visibility) { Gitlab::VisibilityLevel::PUBLIC }
 
         it 'uses the group visibility' do
+          expect(restorer.restore).to eq(true)
           expect(restorer.restored_project.visibility_level).to eq(group_visibility)
         end
       end
@@ -570,6 +573,7 @@ describe Gitlab::ImportExport::ProjectTreeRestorer do
         let(:visibility) { Gitlab::VisibilityLevel::PRIVATE }
 
         it 'uses the project visibility' do
+          expect(restorer.restore).to eq(true)
           expect(restorer.restored_project.visibility_level).to eq(visibility)
         end
       end
@@ -579,6 +583,7 @@ describe Gitlab::ImportExport::ProjectTreeRestorer do
         let(:visibility) { Gitlab::VisibilityLevel::PUBLIC }
 
         it 'uses the group visibility' do
+          expect(restorer.restore).to eq(true)
           expect(restorer.restored_project.visibility_level).to eq(group_visibility)
         end
 
@@ -586,6 +591,7 @@ describe Gitlab::ImportExport::ProjectTreeRestorer do
           it 'sets private visibility' do
             stub_application_setting(restricted_visibility_levels: [Gitlab::VisibilityLevel::INTERNAL])
 
+            expect(restorer.restore).to eq(true)
             expect(restorer.restored_project.visibility_level).to eq(Gitlab::VisibilityLevel::PRIVATE)
           end
         end