Fix PipelineController#index N+1

app/serializers/pipeline_serializer.rb

@@ -43,14 +43,14 @@ class PipelineSerializer < BaseSerializer
       :cancelable_statuses,
       :latest_statuses_ordered_by_stage,
       :latest_builds_report_results,
-      :manual_actions,
       :retryable_builds,
-      :scheduled_actions,
       :stages,
       :latest_statuses,
       :trigger_requests,
       :user,
       {
+        manual_actions: :metadata,
+        scheduled_actions: :metadata,
         downloadable_artifacts: {
           project: [:route, { namespace: :route }],
           job: []

changelogs/unreleased/321788-fix-n-plus-1s.yml

+---
+title: Fix N+1s related to per-build metadata lookups
+merge_request: 55053
+author:
+type: performance

spec/serializers/pipeline_serializer_spec.rb

@@ -209,6 +209,22 @@ RSpec.describe PipelineSerializer do
         end
       end
 
+      context 'with scheduled and manual builds' do
+        let(:ref) { 'feature' }
+
+        before do
+          create(:ci_build, :scheduled, pipeline: resource.first)
+          create(:ci_build, :scheduled, pipeline: resource.second)
+          create(:ci_build, :manual, pipeline: resource.first)
+          create(:ci_build, :manual, pipeline: resource.second)
+        end
+
+        it 'sends at most one metadata query for each type of build', :request_store do
+          # 1 for the existing failed builds and 2 for the added scheduled and manual builds
+          expect { subject }.not_to exceed_query_limit(1 + 2).for_query /SELECT "ci_builds_metadata".*/
+        end
+      end
+
       def create_pipeline(status)
         create(:ci_empty_pipeline,
                project: project,