Destroy user associations in batches

app/models/user.rb

@@ -20,6 +20,7 @@ class User < ApplicationRecord
   include WithUploads
   include OptionallySearch
   include FromUnion
+  include BatchDestroyDependentAssociations
 
   DEFAULT_NOTIFICATION_LEVEL = :participating
 

app/services/users/destroy_service.rb

@@ -56,6 +56,13 @@ module Users
 
       MigrateToGhostUserService.new(user).execute unless options[:hard_delete]
 
+      if Feature.enabled?(:destroy_user_associations_in_batches)
+        # Rails attempts to load all related records into memory before
+        # destroying: https://github.com/rails/rails/issues/22510
+        # This ensures we delete records in batches.
+        user.destroy_dependent_associations_in_batches
+      end
+
       # Destroy the namespace after destroying the user since certain methods may depend on the namespace existing
       user_data = user.destroy
       namespace.destroy

spec/services/users/destroy_service_spec.rb

@@ -20,6 +20,22 @@ describe Users::DestroyService do
         expect { Namespace.find(namespace.id) }.to raise_error(ActiveRecord::RecordNotFound)
       end
 
+      it 'deletes user associations in batches' do
+        expect(user).to receive(:destroy_dependent_associations_in_batches)
+
+        service.execute(user)
+      end
+
+      context 'when :destroy_user_associations_in_batches flag is disabled' do
+        it 'does not delete user associations in batches' do
+          stub_feature_flags(destroy_user_associations_in_batches: false)
+
+          expect(user).not_to receive(:destroy_dependent_associations_in_batches)
+
+          service.execute(user)
+        end
+      end
+
       it 'will delete the project' do
         expect_next_instance_of(Projects::DestroyService) do |destroy_service|
           expect(destroy_service).to receive(:execute).once.and_return(true)