Hide decomposed query behind a feature flag

https://gitlab.com/gitlab-org/gitlab/-/issues/341341

app/finders/ci/pipelines_for_merge_request_finder.rb

@@ -47,12 +47,48 @@ module Ci
 
     private
 
+    # rubocop: disable CodeReuse/ActiveRecord
+    def pipelines_using_cte
+      sha_relation = merge_request.all_commits.select(:sha).distinct
+
+      cte = Gitlab::SQL::CTE.new(:shas, sha_relation)
+
+      pipelines_for_merge_requests = triggered_by_merge_request
+      pipelines_for_branch = filter_by_sha(triggered_for_branch, cte)
+
+      Ci::Pipeline.with(cte.to_arel) # rubocop: disable CodeReuse/ActiveRecord
+        .from_union([pipelines_for_merge_requests, pipelines_for_branch])
+    end
+    # rubocop: enable CodeReuse/ActiveRecord
+
+    def filter_by_sha(pipelines, cte)
+      hex = Arel::Nodes::SqlLiteral.new("'hex'")
+      string_sha = Arel::Nodes::NamedFunction.new('encode', [cte.table[:sha], hex])
+      join_condition = string_sha.eq(Ci::Pipeline.arel_table[:sha])
+
+      filter_by(pipelines, cte, join_condition)
+    end
+
+    def filter_by(pipelines, cte, join_condition)
+      shas_table =
+        Ci::Pipeline.arel_table
+          .join(cte.table, Arel::Nodes::InnerJoin)
+          .on(join_condition)
+          .join_sources
+
+      pipelines.joins(shas_table) # rubocop: disable CodeReuse/ActiveRecord
+    end
+
     def all_pipelines_for_merge_request
-      shas = merge_request.all_commit_shas
-      pipelines_for_merge_request = triggered_by_merge_request
-      pipelines_for_branch = triggered_for_branch.for_sha(shas)
+      if Feature.enabled?(:decomposed_ci_query_in_pipelines_for_merge_request_finder, source_project, default_enabled: :yaml)
+        pipelines_using_cte
+      else
+        shas = merge_request.all_commit_shas
+        pipelines_for_merge_request = triggered_by_merge_request
+        pipelines_for_branch = triggered_for_branch.for_sha(shas)
 
-      Ci::Pipeline.from_union([pipelines_for_merge_request, pipelines_for_branch])
+        Ci::Pipeline.from_union([pipelines_for_merge_request, pipelines_for_branch])
+      end
     end
 
     # NOTE: this method returns only parent merge request pipelines.

config/feature_flags/development/decomposed_ci_query_in_pipelines_for_merge_request_finder.yml

+---
+name: decomposed_ci_query_in_pipelines_for_merge_request_finder
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/68549
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/341341
+milestone: '14.4'
+type: development
+group: group::pipeline execution
+default_enabled: false

spec/finders/ci/pipelines_for_merge_request_finder_spec.rb

@@ -134,117 +134,129 @@ RSpec.describe Ci::PipelinesForMergeRequestFinder do
       end
     end
 
-    context 'when pipelines exist for the branch and merge request' do
-      let(:source_ref) { 'feature' }
-      let(:target_ref) { 'master' }
+    shared_examples 'returns all pipelines for merge request' do
+      context 'when pipelines exist for the branch and merge request' do
+        let(:source_ref) { 'feature' }
+        let(:target_ref) { 'master' }
 
-      let!(:branch_pipeline) do
-        create(:ci_pipeline, source: :push, project: project,
-          ref: source_ref, sha: shas.second)
-      end
-
-      let!(:tag_pipeline) do
-        create(:ci_pipeline, project: project, ref: source_ref, tag: true)
-      end
-
-      let!(:detached_merge_request_pipeline) do
-        create(:ci_pipeline, source: :merge_request_event, project: project,
-          ref: source_ref, sha: shas.second, merge_request: merge_request)
-      end
-
-      let(:merge_request) do
-        create(:merge_request, source_project: project, source_branch: source_ref,
-          target_project: project, target_branch: target_ref)
-      end
-
-      let(:project) { create(:project, :repository) }
-      let(:shas) { project.repository.commits(source_ref, limit: 2).map(&:id) }
-
-      before do
-        create(:merge_request_diff_commit,
-          merge_request_diff: merge_request.merge_request_diff,
-          sha: shas.second, relative_order: 1)
-      end
-
-      it 'returns merge request pipeline first' do
-        expect(subject.all).to eq([detached_merge_request_pipeline, branch_pipeline])
-      end
-
-      context 'when there are a branch pipeline and a merge request pipeline' do
-        let!(:branch_pipeline_2) do
+        let!(:branch_pipeline) do
           create(:ci_pipeline, source: :push, project: project,
-            ref: source_ref, sha: shas.first)
+            ref: source_ref, sha: shas.second)
         end
 
-        let!(:detached_merge_request_pipeline_2) do
-          create(:ci_pipeline, source: :merge_request_event, project: project,
-            ref: source_ref, sha: shas.first, merge_request: merge_request)
+        let!(:tag_pipeline) do
+          create(:ci_pipeline, project: project, ref: source_ref, tag: true)
         end
 
-        it 'returns merge request pipelines first' do
-          expect(subject.all)
-            .to eq([detached_merge_request_pipeline_2,
-                    detached_merge_request_pipeline,
-                    branch_pipeline_2,
-                    branch_pipeline])
+        let!(:detached_merge_request_pipeline) do
+          create(:ci_pipeline, source: :merge_request_event, project: project,
+            ref: source_ref, sha: shas.second, merge_request: merge_request)
         end
-      end
 
-      context 'when there are multiple merge request pipelines from the same branch' do
-        let!(:branch_pipeline_2) do
-          create(:ci_pipeline, source: :push, project: project,
-            ref: source_ref, sha: shas.first)
+        let(:merge_request) do
+          create(:merge_request, source_project: project, source_branch: source_ref,
+            target_project: project, target_branch: target_ref)
         end
 
-        let!(:branch_pipeline_with_sha_not_belonging_to_merge_request) do
-          create(:ci_pipeline, source: :push, project: project, ref: source_ref)
-        end
+        let(:project) { create(:project, :repository) }
+        let(:shas) { project.repository.commits(source_ref, limit: 2).map(&:id) }
 
-        let!(:detached_merge_request_pipeline_2) do
-          create(:ci_pipeline, source: :merge_request_event, project: project,
-            ref: source_ref, sha: shas.first, merge_request: merge_request_2)
+        before do
+          create(:merge_request_diff_commit,
+            merge_request_diff: merge_request.merge_request_diff,
+            sha: shas.second, relative_order: 1)
         end
 
-        let(:merge_request_2) do
-          create(:merge_request, source_project: project, source_branch: source_ref,
-            target_project: project, target_branch: 'stable')
+        it 'returns merge request pipeline first' do
+          expect(subject.all).to eq([detached_merge_request_pipeline, branch_pipeline])
         end
 
-        before do
-          shas.each.with_index do |sha, index|
-            create(:merge_request_diff_commit,
-              merge_request_diff: merge_request_2.merge_request_diff,
-              sha: sha, relative_order: index)
+        context 'when there are a branch pipeline and a merge request pipeline' do
+          let!(:branch_pipeline_2) do
+            create(:ci_pipeline, source: :push, project: project,
+              ref: source_ref, sha: shas.first)
           end
-        end
 
-        it 'returns only related merge request pipelines' do
-          expect(subject.all)
-            .to eq([detached_merge_request_pipeline,
-                    branch_pipeline_2,
-                    branch_pipeline])
+          let!(:detached_merge_request_pipeline_2) do
+            create(:ci_pipeline, source: :merge_request_event, project: project,
+              ref: source_ref, sha: shas.first, merge_request: merge_request)
+          end
 
-          expect(described_class.new(merge_request_2, nil).all)
-            .to eq([detached_merge_request_pipeline_2,
-                    branch_pipeline_2,
-                    branch_pipeline])
+          it 'returns merge request pipelines first' do
+            expect(subject.all)
+              .to eq([detached_merge_request_pipeline_2,
+                      detached_merge_request_pipeline,
+                      branch_pipeline_2,
+                      branch_pipeline])
+          end
         end
-      end
 
-      context 'when detached merge request pipeline is run on head ref of the merge request' do
-        let!(:detached_merge_request_pipeline) do
-          create(:ci_pipeline, source: :merge_request_event, project: project,
-            ref: merge_request.ref_path, sha: shas.second, merge_request: merge_request)
-        end
+        context 'when there are multiple merge request pipelines from the same branch' do
+          let!(:branch_pipeline_2) do
+            create(:ci_pipeline, source: :push, project: project,
+              ref: source_ref, sha: shas.first)
+          end
+
+          let!(:branch_pipeline_with_sha_not_belonging_to_merge_request) do
+            create(:ci_pipeline, source: :push, project: project, ref: source_ref)
+          end
+
+          let!(:detached_merge_request_pipeline_2) do
+            create(:ci_pipeline, source: :merge_request_event, project: project,
+              ref: source_ref, sha: shas.first, merge_request: merge_request_2)
+          end
+
+          let(:merge_request_2) do
+            create(:merge_request, source_project: project, source_branch: source_ref,
+              target_project: project, target_branch: 'stable')
+          end
+
+          before do
+            shas.each.with_index do |sha, index|
+              create(:merge_request_diff_commit,
+                merge_request_diff: merge_request_2.merge_request_diff,
+                sha: sha, relative_order: index)
+            end
+          end
 
-        it 'sets the head ref of the merge request to the pipeline ref' do
-          expect(detached_merge_request_pipeline.ref).to match(%r{refs/merge-requests/\d+/head})
+          it 'returns only related merge request pipelines' do
+            expect(subject.all)
+              .to eq([detached_merge_request_pipeline,
+                      branch_pipeline_2,
+                      branch_pipeline])
+
+            expect(described_class.new(merge_request_2, nil).all)
+              .to eq([detached_merge_request_pipeline_2,
+                      branch_pipeline_2,
+                      branch_pipeline])
+          end
         end
 
-        it 'includes the detached merge request pipeline even though the ref is custom path' do
-          expect(merge_request.all_pipelines).to include(detached_merge_request_pipeline)
+        context 'when detached merge request pipeline is run on head ref of the merge request' do
+          let!(:detached_merge_request_pipeline) do
+            create(:ci_pipeline, source: :merge_request_event, project: project,
+              ref: merge_request.ref_path, sha: shas.second, merge_request: merge_request)
+          end
+
+          it 'sets the head ref of the merge request to the pipeline ref' do
+            expect(detached_merge_request_pipeline.ref).to match(%r{refs/merge-requests/\d+/head})
+          end
+
+          it 'includes the detached merge request pipeline even though the ref is custom path' do
+            expect(merge_request.all_pipelines).to include(detached_merge_request_pipeline)
+          end
         end
       end
     end
+
+    it_behaves_like 'returns all pipelines for merge request'
+
+    context 'when `decomposed_ci_query_in_pipelines_for_merge_request_finder` feature flag disabled' do
+      before do
+        stub_feature_flags(decomposed_ci_query_in_pipelines_for_merge_request_finder: false)
+      end
+
+      it_behaves_like 'returns all pipelines for merge request'
+    end
   end
 end