Add index to workflows.tracker_id (#23743).

git-svn-id: http://svn.redmine.org/redmine/trunk@15859 e93f8b46-1217-0410-a6f0-8f06a7374b81

db/migrate/20161001122012_add_tracker_id_index_to_workflows.rb

@@ -0,0 +1,9 @@
+class AddTrackerIdIndexToWorkflows < ActiveRecord::Migration
+  def self.up
+    add_index :workflows, :tracker_id
+  end
+
+  def self.down
+    remove_index :workflows, :tracker_id
+  end
+end