Skip comparison if head and base pipelines are the same as before

2 files changed, 22 insertions, 6 deletions

diff --git a/app/controllers/projects/merge_requests_controller.rb b/app/controllers/projects/merge_requests_controller.rb
index 5f7f6c66376..2f15cf341b0 100644
--- a/app/controllers/projects/merge_requests_controller.rb
+++ b/app/controllers/projects/merge_requests_controller.rb
@@ -103,10 +103,10 @@ class Projects::MergeRequestsController < Projects::MergeRequests::ApplicationCo
     result = @merge_request.compare_test_reports
 
     case result[:status]
-    when :parsing
+    when :waiting
       render json: '', status: :no_content
-    when :success
-      render json: JSON.parse(result[:data]), status: :ok
+    when :parsed
+      render json: result[:data], status: :ok
     when :error
       render json: { status_reason: result[:status_reason] }, status: :internal_server_error
     else
diff --git a/app/models/merge_request.rb b/app/models/merge_request.rb
index f8434a0873a..9fbd1c023e3 100644
--- a/app/models/merge_request.rb
+++ b/app/models/merge_request.rb
@@ -13,6 +13,7 @@ class MergeRequest < ActiveRecord::Base
   include ReactiveCaching
 
   self.reactive_cache_key = ->(model) { [model.project.id, model.iid] } # For parsing test reports
+  self.reactive_cache_refresh_interval = 10.seconds # TODO: What is the best interval which doesn't make users feel GitLab is slow?
 
   ignore_column :locked_at,
                 :ref_fetched,
@@ -1017,18 +1018,33 @@ class MergeRequest < ActiveRecord::Base
   end
 
   def compare_test_reports
-    with_reactive_cache { |data| return data } || { status: :parsing }
+    with_reactive_cache { |data| data } || { status: :waiting }
   end
 
+  ##
+  # TODO: FE should restart polling if user retried head pipeline.
+  # TODO: How do we deal with the following events?
+  # 1. User retried a head pipeline
+  # 1. User retried a base pipeline
+  # 
+  # To hook the event of base pipeline's retry would be tricky because front-end doesn't hook the evenet today.
   def calculate_reactive_cache
-    return { status: :error, status_reason: 'Missing head pipeline' } unless actual_head_pipeline
+    return { status: :waiting } unless actual_head_pipeline
+    return { status: :waiting } unless actual_head_pipeline.has_test_reports?
+
+    # If base and head pipelines have not been updated, skip the comparison
+    data = Rails.cache.read(full_reactive_cache_key)
+    return data if actual_head_pipeline&.updated_at == data&.dig(:head_pipeline_updated_at) &&
+        base_pipeline&.updated_at == data&.dig(:base_pipeline_updated_at)
 
     begin
       comparer = Gitlab::Ci::Reports::TestReportsComparer
         .new(base_pipeline&.test_reports, actual_head_pipeline&.test_reports)
 
       {
-        status: :success,
+        status: :parsed,
+        head_pipeline_updated_at: actual_head_pipeline.updated_at,
+        base_pipeline_updated_at: base_pipeline&.updated_at,
         data: TestReportsComparerSerializer
           .new(project: project, current_user: nil)
           .represent(comparer).to_json