Add `system` to existing index for notes

changelogs/unreleased/276943-add-non-system-index-to-notes.yml

+---
+title: Update index for notes to include `system`
+merge_request: 48864
+author:
+type: performance

db/migrate/20201201034258_add_index_for_non_system_noteables.rb

+# frozen_string_literal: true
+
+class AddIndexForNonSystemNoteables < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  LEGACY_INDEX_NAME = "index_notes_on_noteable_id_and_noteable_type"
+  NEW_INDEX_NAME = "index_notes_on_noteable_id_and_noteable_type_and_system"
+
+  def up
+    add_concurrent_index :notes, [:noteable_id, :noteable_type, :system], name: NEW_INDEX_NAME
+
+    remove_concurrent_index_by_name :notes, LEGACY_INDEX_NAME
+  end
+
+  def down
+    add_concurrent_index :notes, [:noteable_id, :noteable_type], name: LEGACY_INDEX_NAME
+
+    remove_concurrent_index_by_name :notes, NEW_INDEX_NAME
+  end
+end

db/schema_migrations/20201201034258

+12cc1beb73bcc31f6546066842913284aabba22ea4e93095271c0cfdacfd0858
\ No newline at end of file

db/structure.sql

@@ -21734,7 +21734,7 @@ CREATE INDEX index_notes_on_line_code ON notes USING btree (line_code);
 
 CREATE INDEX index_notes_on_note_trigram ON notes USING gin (note gin_trgm_ops);
 
-CREATE INDEX index_notes_on_noteable_id_and_noteable_type ON notes USING btree (noteable_id, noteable_type);
+CREATE INDEX index_notes_on_noteable_id_and_noteable_type_and_system ON notes USING btree (noteable_id, noteable_type, system);
 
 CREATE INDEX index_notes_on_project_id_and_id_and_system_false ON notes USING btree (project_id, id) WHERE (NOT system);