Fix and expand Gitaly FindCommit caching

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/26248 added
support for deduplicating FindCommit requests using Gitaly ref name
caching. However, not all endpoints were covered, and in one case the
Gitaly wrapper wasn't actually surrounding the serialization step. We
can safely cache ref names between FindCommit calls for #index and #show
endpoints for merge requests and pipelines. This can significantly
reduce the number of FindCommit requests.

app/controllers/projects/application_controller.rb

@@ -88,4 +88,10 @@ class Projects::ApplicationController < ApplicationController
   def check_issues_available!
     return render_404 unless @project.feature_available?(:issues, current_user)
   end
+
+  def allow_gitaly_ref_name_caching
+    ::Gitlab::GitalyClient.allow_ref_name_caching do
+      yield
+    end
+  end
 end

app/controllers/projects/merge_requests_controller.rb

@@ -16,6 +16,8 @@ class Projects::MergeRequestsController < Projects::MergeRequests::ApplicationCo
   before_action :authenticate_user!, only: [:assign_related_issues]
   before_action :check_user_can_push_to_source_branch!, only: [:rebase]
 
+  around_action :allow_gitaly_ref_name_caching, only: [:index, :show]
+
   def index
     @merge_requests = @issuables
 
@@ -315,10 +317,8 @@ class Projects::MergeRequestsController < Projects::MergeRequests::ApplicationCo
   end
 
   def serializer
-    ::Gitlab::GitalyClient.allow_ref_name_caching do
     MergeRequestSerializer.new(current_user: current_user, project: merge_request.project)
   end
-  end
 
   def define_edit_vars
     @source_project = @merge_request.source_project

app/controllers/projects/pipelines_controller.rb

@@ -8,6 +8,8 @@ class Projects::PipelinesController < Projects::ApplicationController
   before_action :authorize_create_pipeline!, only: [:new, :create]
   before_action :authorize_update_pipeline!, only: [:retry, :cancel]
 
+  around_action :allow_gitaly_ref_name_caching, only: [:index, :show]
+
   wrap_parameters Ci::Pipeline
 
   POLLING_INTERVAL = 10_000
@@ -148,13 +150,11 @@ class Projects::PipelinesController < Projects::ApplicationController
   private
 
   def serialize_pipelines
-    ::Gitlab::GitalyClient.allow_ref_name_caching do
     PipelineSerializer
       .new(project: @project, current_user: @current_user)
       .with_pagination(request, response)
       .represent(@pipelines, disable_coverage: true, preload: true)
   end
-  end
 
   def render_show
     respond_to do |format|

changelogs/unreleased/sh-fix-ref-name-caching.yml

+---
+title: Fix and expand Gitaly FindCommit caching
+merge_request: 27018
+author:
+type: performance

spec/controllers/projects/merge_requests_controller_spec.rb

@@ -60,6 +60,8 @@ describe Projects::MergeRequestsController do
       end
 
       it "renders merge request page" do
+        expect(::Gitlab::GitalyClient).to receive(:allow_ref_name_caching).and_call_original
+
         go(format: :html)
 
         expect(response).to be_success

spec/controllers/projects/pipelines_controller_spec.rb

@@ -97,6 +97,8 @@ describe Projects::PipelinesController do
         RequestStore.clear!
         RequestStore.begin!
 
+        expect(::Gitlab::GitalyClient).to receive(:allow_ref_name_caching).and_call_original
+
         expect { get_pipelines_index_json }
           .to change { Gitlab::GitalyClient.get_request_count }.by(2)
       end