Cache FindCommit results in pipelines view

For each pipeline, the controller will call `Pipeline#latest?` to
determine if the pipeline's ref is the latest for that branch.
Since it's likely that the same branches are being used in each
pipeline, we can reduce Gitaly overhead by caching the results
of the FindCommit call.

app/controllers/projects/pipelines_controller.rb

@@ -31,10 +31,7 @@ class Projects::PipelinesController < Projects::ApplicationController
         Gitlab::PollingInterval.set_header(response, interval: POLLING_INTERVAL)
 
         render json: {
-          pipelines: PipelineSerializer
-            .new(project: @project, current_user: @current_user)
-            .with_pagination(request, response)
-            .represent(@pipelines, disable_coverage: true, preload: true),
+          pipelines: serialize_pipelines,
           count: {
             all: @pipelines_count,
             running: @running_count,
@@ -150,6 +147,15 @@ 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|
       format.html do

changelogs/unreleased/sh-cache-pipeline-find-commits.yml

+---
+title: Cache FindCommit results in pipelines view
+merge_request: 26776
+author:
+type: performance

spec/controllers/projects/pipelines_controller_spec.rb

@@ -28,6 +28,8 @@ describe Projects::PipelinesController do
       end
 
       it 'returns serialized pipelines', :request_store do
+        expect(::Gitlab::GitalyClient).to receive(:allow_ref_name_caching).and_call_original
+
         queries = ActiveRecord::QueryRecorder.new do
           get_pipelines_index_json
         end