Delete events in batches when project is destroyed

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

**Problem**

The previous attempt to extract delete events query from project
delete did not help to resolve the statement timeout problem.

**Solution**

Use batch delete for events.

Changelog: changed

app/services/events/destroy_service.rb

@@ -2,20 +2,29 @@
 
 module Events
   class DestroyService
+    BATCH_SIZE = 50
+
     def initialize(project)
       @project = project
     end
 
     def execute
-      project.events.all.delete_all
+      loop do
+        count = delete_events_in_batches
+        break if count < BATCH_SIZE
+      end
 
       ServiceResponse.success(message: 'Events were deleted.')
-    rescue StandardError
-      ServiceResponse.error(message: 'Failed to remove events.')
+    rescue StandardError => e
+      ServiceResponse.error(message: e.message)
     end
 
     private
 
     attr_reader :project
+
+    def delete_events_in_batches
+      project.events.limit(BATCH_SIZE).delete_all
+    end
   end
 end

app/services/projects/destroy_service.rb

@@ -80,8 +80,14 @@ module Projects
     end
 
     def remove_events
+      log_info("Attempting to destroy events from #{project.full_path} (#{project.id})")
+
       response = ::Events::DestroyService.new(project).execute
 
+      if response.error?
+        log_error("Event deletion failed on #{project.full_path} with the following message: #{response.message}")
+      end
+
       response.success?
     end
 

spec/services/events/destroy_service_spec.rb

@@ -30,16 +30,28 @@ RSpec.describe Events::DestroyService do
       expect(unrelated_event.reload).to be_present
     end
 
+    context 'batch delete' do
+      before do
+        stub_const("#{described_class}::BATCH_SIZE", 2)
+      end
+
+      it 'splits delete queries into batches' do
+        expect(project).to receive(:events).twice.and_call_original
+
+        subject.execute
+      end
+    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)
+        allow(project).to receive_message_chain(:events, :limit, :delete_all).and_raise(ActiveRecord::ActiveRecordError, 'custom error')
       end
 
       it 'returns error' do
         response = subject.execute
 
         expect(response).to be_error
-        expect(response.message).to eq 'Failed to remove events.'
+        expect(response.message).to eq 'custom error'
       end
 
       it 'does not delete events' do