Improve issue load time performance by avoiding ORDER BY in find_by call

The Sortable concern has a default scope that adds ORDER BY to all queries. EXPLAIN ANALYZE shows that this additional ORDER BY statement causes the SQL optimizer to use the wrong index, which leads to a load time of 2.9 s vs 0.073 ms just for the SELECT call. The minimal change here is to re-implement find_by using where and reorder to remove the ORDER BY clause in IssuesController#index. Closes #23075

Improve issue load time performance by avoiding ORDER BY in find_by call
aada0103 · Stan Hu · 63201925 · aada0103 · aada0103
Commit aada0103 authored Oct 06, 2016 by Stan Hu
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CHANGELOG CHANGELOG +1 -0

issues_controller.rb app/controllers/projects/issues_controller.rb +2 -1

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--- a/CHANGELOG
+++ b/CHANGELOG
@@ -3,6 +3,7 @@ Please view this file on the master branch, on stable branches it's out of date.
 v 8.13.0 (unreleased)
  - Update runner version only when updating contacted_at
  - Add link from system note to compare with previous version
+  - Improve issue load time performance by avoiding ORDER BY in find_by call
  - Use gitlab-shell v3.6.2 (GIT TRACE logging)
  - Fix centering of custom header logos (Ashley Dumaine)
  - AbstractReferenceFilter caches project_refs on RequestStore when active

--- a/app/controllers/projects/issues_controller.rb
+++ b/app/controllers/projects/issues_controller.rb
@@ -159,7 +159,8 @@ class Projects::IssuesController < Projects::ApplicationController
  protected

  def issue
-    @noteable = @issue ||= @project.issues.find_by(iid: params[:id]) || redirect_old
+    # The Sortable default scope causes performance issues when used with find_by
+    @noteable = @issue ||= @project.issues.where(iid: params[:id]).reorder(nil).take || redirect_old
  end
  alias_method :subscribable_resource, :issue
  alias_method :issuable, :issue