Avoid cross-joins in PipelinesForMergeRequestFinder

Separate DB queries to avoid cross-joins in
`Ci::PipelinesForMergeRequestFinder`

Changelog: performance

app/finders/ci/pipelines_for_merge_request_finder.rb

@@ -31,67 +31,27 @@ module Ci
 
     # Fetch all pipelines without permission check.
     def all
-      ::Gitlab::Database.allow_cross_joins_across_databases(url: 'https://gitlab.com/gitlab-org/gitlab/-/issues/336891') do
-        strong_memoize(:all_pipelines) do
-          next Ci::Pipeline.none unless source_project
+      strong_memoize(:all_pipelines) do
+        next Ci::Pipeline.none unless source_project
 
-          pipelines =
-            if merge_request.persisted?
-              all_pipelines_for_merge_request
-            else
-              triggered_for_branch.for_sha(commit_shas)
-            end
+        pipelines =
+          if merge_request.persisted?
+            all_pipelines_for_merge_request
+          else
+            triggered_for_branch.for_sha(commit_shas)
+          end
 
-          pipelines = pipelines.allow_cross_joins_across_databases(url: 'https://gitlab.com/gitlab-org/gitlab/-/issues/336891')
-
-          sort(pipelines)
-        end
+        sort(pipelines)
       end
     end
 
     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
-      if Feature.enabled?(:decomposed_ci_query_in_pipelines_for_merge_request_finder, target_project, default_enabled: :yaml)
-        pipelines_for_merge_request = triggered_by_merge_request
-        pipelines_for_branch = triggered_for_branch.for_sha(recent_diff_head_shas(COMMITS_LIMIT))
+      pipelines_for_merge_request = triggered_by_merge_request
+      pipelines_for_branch = triggered_for_branch.for_sha(recent_diff_head_shas(COMMITS_LIMIT))
 
-        Ci::Pipeline.from_union([pipelines_for_merge_request, pipelines_for_branch])
-      else
-        pipelines_using_cte
-      end
+      Ci::Pipeline.from_union([pipelines_for_merge_request, pipelines_for_branch])
     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

@@ -135,86 +135,6 @@ RSpec.describe Ci::PipelinesForMergeRequestFinder do
     end
 
     context 'when pipelines exist for the branch and merge request' do
-      shared_examples 'returns all pipelines for merge request' do
-        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
-            create(:ci_pipeline, source: :push, project: project,
-                   ref: source_ref, sha: shas.first)
-          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)
-          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])
-          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)
-          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 '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 match_array([detached_merge_request_pipeline_2, branch_pipeline_2, branch_pipeline])
-          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
-
-          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
-
       let(:source_ref) { 'feature' }
       let(:target_ref) { 'master' }
 
@@ -240,20 +160,76 @@ RSpec.describe Ci::PipelinesForMergeRequestFinder do
       let(:project) { create(:project, :repository) }
       let(:shas) { project.repository.commits(source_ref, limit: 2).map(&:id) }
 
-      context 'when `decomposed_ci_query_in_pipelines_for_merge_request_finder` feature flag enabled' do
-        before do
-          stub_feature_flags(decomposed_ci_query_in_pipelines_for_merge_request_finder: merge_request.target_project)
+      it 'returns merge request pipeline first' do
+        expect(subject.all).to match_array([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
+          create(:ci_pipeline, source: :push, project: project,
+                 ref: source_ref, sha: shas.first)
+        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)
         end
 
-        it_behaves_like 'returns all pipelines for merge request'
+        it 'returns merge request pipelines first' do
+          expect(subject.all)
+            .to match_array([detached_merge_request_pipeline_2, detached_merge_request_pipeline, branch_pipeline_2, branch_pipeline])
+        end
       end
 
-      context 'when `decomposed_ci_query_in_pipelines_for_merge_request_finder` feature flag disabled' do
+      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
-          stub_feature_flags(decomposed_ci_query_in_pipelines_for_merge_request_finder: false)
+          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_behaves_like 'returns all pipelines for merge request'
+        it 'returns only related merge request pipelines' do
+          expect(subject.all).to match_array([detached_merge_request_pipeline, branch_pipeline_2, branch_pipeline])
+
+          expect(described_class.new(merge_request_2, nil).all)
+            .to match_array([detached_merge_request_pipeline_2, branch_pipeline_2, branch_pipeline])
+        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
+
+        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