Batch-load environments in EE pipelines

This fixes an N+1 when rendering the pipeline tab.

app/models/ci/build.rb

@@ -73,7 +73,14 @@ module Ci
       return unless has_environment?
 
       strong_memoize(:persisted_environment) do
-        Environment.find_by(name: expanded_environment_name, project: project)
+        # This code path has caused N+1s in the past, since environments are only indirectly
+        # associated to builds and pipelines; see https://gitlab.com/gitlab-org/gitlab/-/issues/326445
+        # We therefore batch-load them to prevent dormant N+1s until we found a proper solution.
+        BatchLoader.for(expanded_environment_name).batch(key: project_id) do |names, loader, args|
+          Environment.where(name: names, project: args[:key]).find_each do |environment|
+            loader.call(environment.name, environment)
+          end
+        end
       end
     end
 

ee/app/policies/ee/ci/build_policy.rb

@@ -36,10 +36,12 @@ module EE
 
         def deployable_by_user?
           # We need to check if Protected Environments feature is available,
+          # and whether there is an environment defined for the current build,
           # as evaluating `build.expanded_environment_name` is expensive.
+          return true unless build.has_environment?
           return true unless build.project.protected_environments_feature_available?
 
-          build.project.protected_environment_accessible_to?(build.persisted_environment&.name, user)
+          build.project.protected_environment_accessible_to?(build.expanded_environment_name, user)
         end
       end
     end

ee/changelogs/unreleased/321788-fix-environment-nplus1.yml

+---
+title: Batch-load environments in EE pipelines
+merge_request: 57706
+author:
+type: performance

spec/serializers/pipeline_serializer_spec.rb

@@ -209,6 +209,25 @@ RSpec.describe PipelineSerializer do
         end
       end
 
+      context 'with build environments' do
+        let(:ref) { 'feature' }
+
+        it 'verifies number of queries', :request_store do
+          stub_licensed_features(protected_environments: true)
+
+          env = create(:environment, project: project)
+          create(:ci_build, :scheduled, project: project, environment: env.name)
+          create(:ci_build, :scheduled, project: project, environment: env.name)
+          create(:ci_build, :scheduled, project: project, environment: env.name)
+
+          recorded = ActiveRecord::QueryRecorder.new { subject }
+          expected_queries = Gitlab.ee? ? 61 : 57
+
+          expect(recorded.count).to be_within(1).of(expected_queries)
+          expect(recorded.cached_count).to eq(0)
+        end
+      end
+
       context 'with scheduled and manual builds' do
         let(:ref) { 'feature' }