Move issue placement to its own worker

This adds an issue_placement_worker that places recently created
unpositioned issues either at the end or the start of the issue set.

app/workers/issue_placement_worker.rb

+# frozen_string_literal: true
+
+class IssuePlacementWorker
+  include ApplicationWorker
+
+  idempotent!
+  feature_category :issue_tracking
+  urgency :high
+  worker_resource_boundary :cpu
+  weight 2
+
+  # rubocop: disable CodeReuse/ActiveRecord
+  def perform(issue_id, placement = :end)
+    issue = Issue.find(issue_id)
+
+    to_place = Issue
+      .relative_positioning_query_base(issue)
+      .where(Issue.arel_table[:created_at].gteq(issue.created_at - 5.minutes))
+      .order_created_at_desc
+
+    if placement == :end
+      Issue.move_nulls_to_end(to_place.to_a.reverse)
+    elsif placement == :start
+      Issue.move_nulls_to_start(to_place.to_a)
+    end
+  rescue ActiveRecord::RecordNotFound, RelativePositioning::NoSpaceLeft => e
+    Gitlab::ErrorTracking.log_exception(e, issue_id: issue_id, placement: placement)
+    IssueRebalancingWorker.perform_async(nil, issue.project_id) if issue && e.is_a?(RelativePositioning::NoSpaceLeft)
+  end
+  # rubocop: enable CodeReuse/ActiveRecord
+end

app/workers/new_issue_worker.rb

@@ -12,10 +12,10 @@ class NewIssueWorker # rubocop:disable Scalability/IdempotentWorker
   def perform(issue_id, user_id)
     return unless objects_found?(issue_id, user_id)
 
-    ::Issues::ReorderService.new(nil, user, placement: :end).execute(issuable)
     ::EventCreateService.new.open_issue(issuable, user)
     ::NotificationService.new.new_issue(issuable, user)
     issuable.create_cross_references!(user)
+    IssuePlacementWorker.perform_async(issue_id, :end)
   end
 
   def issuable_class

spec/workers/issue_placement_worker_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe IssuePlacementWorker do
+  describe '#perform' do
+    let_it_be(:project) { create_default(:project) }
+    let_it_be(:issue) { create(:issue, relative_position: nil) }
+    let_it_be(:issue_a) { create(:issue, relative_position: nil, created_at: issue.created_at - 1.minute) }
+    let_it_be(:issue_b) { create(:issue, relative_position: nil, created_at: issue.created_at - 6.minutes) }
+    let_it_be(:issue_c) { create(:issue, relative_position: nil, created_at: issue.created_at + 1.minute) }
+    let_it_be(:issue_d) { create(:issue, relative_position: nil, created_at: issue.created_at + 6.minutes) }
+    let_it_be(:issue_e) { create(:issue, relative_position: 10, created_at: issue.created_at + 3.minutes) }
+
+    let_it_be(:irrelevant) { create(:issue, project: create(:project), created_at: issue.created_at - 30.seconds) }
+
+    it 'places all issues created at most 5 minutes before this one at the end, most recent last' do
+      described_class.new.perform(issue.id, :end)
+
+      expect(project.issues.order_relative_position_asc)
+        .to eq([issue_e, issue_a, issue, issue_c, issue_d, issue_b])
+    end
+
+    it 'places all issues created at most 5 minutes before this one at the start, most recent first' do
+      described_class.new.perform(issue.id, :start)
+
+      expect(project.issues.order_relative_position_asc)
+        .to eq([issue_d, issue_c, issue, issue_a, issue_e, issue_b])
+    end
+
+    it 'anticipates the failure to find the issue' do
+      id = non_existing_record_id
+
+      expect(Gitlab::ErrorTracking)
+        .to receive(:log_exception)
+        .with(ActiveRecord::RecordNotFound, issue_id: id, placement: :end)
+
+      described_class.new.perform(id, :end)
+    end
+
+    it 'anticipates the failure to place the issues, and schedules rebalancing' do
+      allow(Issue).to receive(:move_nulls_to_end) { raise RelativePositioning::NoSpaceLeft }
+
+      expect(IssueRebalancingWorker).to receive(:perform_async).with(nil, project.id)
+      expect(Gitlab::ErrorTracking)
+        .to receive(:log_exception)
+        .with(RelativePositioning::NoSpaceLeft, issue_id: issue.id, placement: :end)
+
+      described_class.new.perform(issue.id, :end)
+    end
+  end
+end

spec/workers/new_issue_worker_spec.rb

@@ -49,10 +49,9 @@ RSpec.describe NewIssueWorker do
       end
 
       it 'moves the issue to the end' do
-        other_issue = create(:issue, project: project, relative_position: 100)
+        expect(IssuePlacementWorker).to receive(:perform_async).with(issue.id, :end)
 
-        expect { worker.perform(issue.id, user.id) }
-          .to change { issue.reset.relative_position }.to(be > other_issue.relative_position)
+        worker.perform(issue.id, user.id)
       end
 
       it 'creates a notification for the mentioned user' do