Delete project events before the project

Contributes to https://gitlab.com/gitlab-org/gitlab/-/issues/346169

**Problem**

We delete events via cascade delete. But it leads to a higher chance
of the statement timeout error for `DELETE FROM project` query.

**Solution**

Delete events before the project in a separate statement to avoid a
query timeout.

Changelog: added

app/services/events/destroy_service.rb

+# frozen_string_literal: true
+
+module Events
+  class DestroyService
+    def initialize(project)
+      @project = project
+    end
+
+    def execute
+      project.events.all.delete_all
+
+      ServiceResponse.success(message: 'Events were deleted.')
+    rescue StandardError
+      ServiceResponse.error(message: 'Failed to remove events.')
+    end
+
+    private
+
+    attr_reader :project
+  end
+end

app/services/projects/destroy_service.rb

@@ -75,6 +75,18 @@ module Projects
       response.success?
     end
 
+    def destroy_events!
+      unless remove_events
+        raise_error(s_('DeleteProject|Failed to remove events. Please try again or contact administrator.'))
+      end
+    end
+
+    def remove_events
+      response = ::Events::DestroyService.new(project).execute
+
+      response.success?
+    end
+
     def remove_repository(repository)
       return true unless repository
 
@@ -117,6 +129,7 @@ module Projects
       log_destroy_event
       trash_relation_repositories!
       trash_project_repositories!
+      destroy_events!
       destroy_web_hooks!
       destroy_project_bots!
 

locale/gitlab.pot

@@ -11357,6 +11357,9 @@ msgstr ""
 msgid "Delete variable"
 msgstr ""
 
+msgid "DeleteProject|Failed to remove events. Please try again or contact administrator."
+msgstr ""
+
 msgid "DeleteProject|Failed to remove project repository. Please try again or contact administrator."
 msgstr ""
 

spec/services/events/destroy_service_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Events::DestroyService do
+  subject(:service) { described_class.new(project) }
+
+  let_it_be(:project, reload: true) { create(:project, :repository) }
+  let_it_be(:another_project) { create(:project) }
+  let_it_be(:merge_request) { create(:merge_request, source_project: project) }
+  let_it_be(:user) { create(:user) }
+
+  let!(:unrelated_event) { create(:event, :merged, project: another_project, target: another_project, author: user) }
+
+  before do
+    create(:event, :created, project: project, target: project, author: user)
+    create(:event, :created, project: project, target: merge_request, author: user)
+    create(:event, :merged, project: project, target: merge_request, author: user)
+  end
+
+  let(:events) { project.events }
+
+  describe '#execute', :aggregate_failures do
+    it 'deletes the events' do
+      response = nil
+
+      expect { response = subject.execute }.to change(Event, :count).by(-3)
+
+      expect(response).to be_success
+      expect(unrelated_event.reload).to be_present
+    end
+
+    context 'when an error is raised while deleting the records' do
+      before do
+        allow(project).to receive_message_chain(:events, :all, :delete_all).and_raise(ActiveRecord::ActiveRecordError)
+      end
+
+      it 'returns error' do
+        response = subject.execute
+
+        expect(response).to be_error
+        expect(response.message).to eq 'Failed to remove events.'
+      end
+
+      it 'does not delete events' do
+        expect { subject.execute }.not_to change(Event, :count)
+      end
+    end
+  end
+end

spec/services/projects/destroy_service_spec.rb

@@ -545,6 +545,27 @@ RSpec.describe Projects::DestroyService, :aggregate_failures do
     end
   end
 
+  context 'when project has events' do
+    let!(:event) { create(:event, :created, project: project, target: project, author: user) }
+
+    it 'deletes events from the project' do
+      expect do
+        destroy_project(project, user)
+      end.to change(Event, :count).by(-1)
+    end
+
+    context 'when an error is returned while deleting events' do
+      it 'does not delete project' do
+        allow_next_instance_of(Events::DestroyService) do |instance|
+          allow(instance).to receive(:execute).and_return(ServiceResponse.error(message: 'foo'))
+        end
+
+        expect(destroy_project(project, user)).to be_falsey
+        expect(project.delete_error).to include('Failed to remove events')
+      end
+    end
+  end
+
   context 'error while destroying', :sidekiq_inline do
     let!(:pipeline) { create(:ci_pipeline, project: project) }
     let!(:builds) { create_list(:ci_build, 2, :artifacts, pipeline: pipeline) }