Remove feature flag export_fast_serialize

- Remove feature flag from specs
- Remove feature flag from LegacyTreeSaver

changelogs/unreleased/212463-remove-export-fast-serialize-feature-flag.yml

+---
+title: Remove feature flag 'export_fast_serialize' and 'export_fast_serialize_with_raw_json'
+merge_request: 28037
+author:
+type: performance

lib/gitlab/import_export/fast_hash_serializer.rb

@@ -142,12 +142,7 @@ module Gitlab
           # returned by database when no `ORDER` is specified
           batch = batch.reorder(batch.klass.primary_key)
 
-          if Feature.enabled?(:export_fast_serialize_with_raw_json, default_enabled: true)
           data.append(JSONBatchRelation.new(batch, options, preloads[key]).tap(&:raw_json))
-          else
-            batch = batch.preload(preloads[key]) if preloads&.key?(key)
-            data += batch.as_json(options)
-          end
         end
 
         data

lib/gitlab/import_export/legacy_relation_tree_saver.rb

@@ -6,13 +6,9 @@ module Gitlab
       include Gitlab::ImportExport::CommandLineUtil
 
       def serialize(exportable, relations_tree)
-        if Feature.enabled?(:export_fast_serialize, default_enabled: true)
         Gitlab::ImportExport::FastHashSerializer
           .new(exportable, relations_tree)
           .execute
-        else
-          exportable.as_json(relations_tree)
-        end
       end
 
       def save(tree, dir_path, filename)

spec/lib/gitlab/import_export/group/tree_saver_spec.rb

@@ -23,50 +23,6 @@ describe Gitlab::ImportExport::Group::TreeSaver do
       expect(group_tree_saver.save).to be true
     end
 
-    context ':export_fast_serialize feature flag checks' do
-      before do
-        expect(Gitlab::ImportExport::Reader).to receive(:new).with(shared: shared, config: group_config).and_return(reader)
-        expect(reader).to receive(:group_tree).and_return(group_tree)
-      end
-
-      let(:reader) { instance_double('Gitlab::ImportExport::Reader') }
-      let(:group_config) { Gitlab::ImportExport::Config.new(config: Gitlab::ImportExport.group_config_file).to_h }
-      let(:group_tree) do
-        {
-          include: [{ milestones: { include: [] } }],
-          preload: { milestones: nil }
-        }
-      end
-
-      context 'when :export_fast_serialize feature is enabled' do
-        let(:serializer) { instance_double(Gitlab::ImportExport::FastHashSerializer) }
-
-        before do
-          stub_feature_flags(export_fast_serialize: true)
-
-          expect(Gitlab::ImportExport::FastHashSerializer).to receive(:new).with(group, group_tree).and_return(serializer)
-        end
-
-        it 'uses FastHashSerializer' do
-          expect(serializer).to receive(:execute)
-
-          group_tree_saver.save
-        end
-      end
-
-      context 'when :export_fast_serialize feature is disabled' do
-        before do
-          stub_feature_flags(export_fast_serialize: false)
-        end
-
-        it 'is serialized via built-in `as_json`' do
-          expect(group).to receive(:as_json).with(group_tree).and_call_original
-
-          group_tree_saver.save
-        end
-      end
-    end
-
     # It is mostly duplicated in
     # `spec/lib/gitlab/import_export/fast_hash_serializer_spec.rb`
     # except:

spec/lib/gitlab/import_export/legacy_relation_tree_saver_spec.rb

@@ -8,13 +8,8 @@ describe Gitlab::ImportExport::LegacyRelationTreeSaver do
   let(:tree) { {} }
 
   describe '#serialize' do
-    context 'when :export_fast_serialize feature is enabled' do
     let(:serializer) { instance_double(Gitlab::ImportExport::FastHashSerializer) }
 
-      before do
-        stub_feature_flags(export_fast_serialize: true)
-      end
-
     it 'uses FastHashSerializer' do
       expect(Gitlab::ImportExport::FastHashSerializer)
         .to receive(:new)
@@ -26,17 +21,4 @@ describe Gitlab::ImportExport::LegacyRelationTreeSaver do
       relation_tree_saver.serialize(exportable, tree)
     end
   end
-
-    context 'when :export_fast_serialize feature is disabled' do
-      before do
-        stub_feature_flags(export_fast_serialize: false)
-      end
-
-      it 'is serialized via built-in `as_json`' do
-        expect(exportable).to receive(:as_json).with(tree)
-
-        relation_tree_saver.serialize(exportable, tree)
-      end
-    end
-  end
 end

spec/lib/gitlab/import_export/project/legacy_tree_saver_spec.rb

@@ -25,51 +25,6 @@ describe Gitlab::ImportExport::Project::LegacyTreeSaver do
       expect(project_tree_saver.save).to be true
     end
 
-    context ':export_fast_serialize feature flag checks' do
-      before do
-        expect(Gitlab::ImportExport::Reader).to receive(:new).with(shared: shared).and_return(reader)
-        expect(reader).to receive(:project_tree).and_return(project_tree)
-      end
-
-      let(:serializer) { instance_double('Gitlab::ImportExport::FastHashSerializer') }
-      let(:reader) { instance_double('Gitlab::ImportExport::Reader') }
-      let(:project_tree) do
-        {
-          include: [{ issues: { include: [] } }],
-          preload: { issues: nil }
-        }
-      end
-
-      context 'when :export_fast_serialize feature is enabled' do
-        before do
-          stub_feature_flags(export_fast_serialize: true)
-        end
-
-        it 'uses FastHashSerializer' do
-          expect(Gitlab::ImportExport::FastHashSerializer)
-            .to receive(:new)
-            .with(project, project_tree)
-            .and_return(serializer)
-
-          expect(serializer).to receive(:execute)
-
-          project_tree_saver.save
-        end
-      end
-
-      context 'when :export_fast_serialize feature is disabled' do
-        before do
-          stub_feature_flags(export_fast_serialize: false)
-        end
-
-        it 'is serialized via built-in `as_json`' do
-          expect(project).to receive(:as_json).with(project_tree)
-
-          project_tree_saver.save
-        end
-      end
-    end
-
     # It is mostly duplicated in
     # `spec/lib/gitlab/import_export/fast_hash_serializer_spec.rb`
     # except: