Merge branch 'ab-60524-optimize-query' into 'master'

Optimize count query by using a limited count only

See merge request gitlab-org/gitlab-ee!12231

ee/app/models/ee/project.rb

@@ -79,12 +79,13 @@ module EE
 
       scope :mirror, -> { where(mirror: true) }
 
-      scope :mirrors_to_sync, ->(freeze_at) do
+      scope :mirrors_to_sync, ->(freeze_at, limit: nil) do
         mirror
           .joins_import_state
           .where.not(import_state: { status: [:scheduled, :started] })
           .where("import_state.next_execution_timestamp <= ?", freeze_at)
           .where("import_state.retry_count <= ?", ::Gitlab::Mirror::MAX_RETRY)
+          .limit(limit)
       end
 
       scope :with_wiki_enabled, -> { with_feature_enabled(:wiki) }

ee/changelogs/unreleased/ab-60524-optimize-query.yml

+---
+title: Limit count to improve query performance
+merge_request: 12231
+author:
+type: performance

ee/lib/gitlab/mirror.rb

@@ -37,11 +37,11 @@ module Gitlab
         return false if available_spots < capacity_threshold
 
         # Only reschedule if we are able to completely fill up the available spots.
-        mirrors_ready_to_sync_count >= available_spots
+        mirrors_ready_to_sync_count(available_spots) >= available_spots
       end
 
-      def mirrors_ready_to_sync_count
-        Project.mirrors_to_sync(Time.now).count
+      def mirrors_ready_to_sync_count(up_to = nil)
+        Project.mirrors_to_sync(Time.now, limit: up_to).count
       end
 
       def available_capacity

ee/spec/models/project_spec.rb

@@ -191,6 +191,17 @@ describe Project do
 
         expect(described_class.mirrors_to_sync(timestamp)).to be_empty
       end
+
+      context 'when a limit is applied' do
+        before do
+          another_project = create(:project)
+          create(:import_state, :mirror, :finished, project: another_project)
+        end
+
+        it 'returns project if next_execution_timestamp is not in the future' do
+          expect(described_class.mirrors_to_sync(timestamp, limit: 1)).to match_array(project)
+        end
+      end
     end
 
     context 'when project is failed' do