Sleep between inserting batches of refreshes

This inserts a short nap so replication can catch up before the next
batch.

This will add about 25m of doing nothing to the rake task for the 700k
records we expect to insert. But it's not like I'll be actively
waiting for this to complete.

lib/tasks/gitlab/refresh_project_statistics_build_artifacts_size.rake

@@ -28,11 +28,14 @@ namespace :gitlab do
         projects = Project.where(id: ids)
         Projects::BuildArtifactsSizeRefresh.enqueue_refresh(projects)
 
+        # Take a short break to allow replication to catch up
+        Kernel.sleep(1)
+
         imported += projects.size
         missing += ids.size - projects.size
         puts "#{imported}/#{project_ids.size} (missing projects: #{missing})"
       end
-      puts 'Done.'.green
+      puts 'Done.'
     else
       puts 'Project IDs must be listed in the CSV under the header PROJECT_ID'.red
     end

spec/tasks/gitlab/refresh_project_statistics_build_artifacts_size_rake_spec.rb

@@ -27,6 +27,7 @@ RSpec.describe 'gitlab:refresh_project_statistics_build_artifacts_size rake task
       stub_const("BUILD_ARTIFACTS_SIZE_REFRESH_ENQUEUE_BATCH_SIZE", 2)
 
       stub_request(:get, csv_url).to_return(status: 200, body: csv_body)
+      allow(Kernel).to receive(:sleep).with(1)
     end
 
     context 'when given a list of space-separated IDs through rake argument' do
@@ -35,6 +36,14 @@ RSpec.describe 'gitlab:refresh_project_statistics_build_artifacts_size rake task
 
         expect(Projects::BuildArtifactsSizeRefresh.all.map(&:project)).to match_array([project_1, project_2, project_3])
       end
+
+      it 'inserts refreshes in batches with a sleep' do
+        expect(Projects::BuildArtifactsSizeRefresh).to receive(:enqueue_refresh).with([project_1, project_2]).ordered
+        expect(Kernel).to receive(:sleep).with(1)
+        expect(Projects::BuildArtifactsSizeRefresh).to receive(:enqueue_refresh).with([project_3]).ordered
+
+        run_rake_task(rake_task, csv_url)
+      end
     end
 
     context 'when CSV has invalid header' do