fix 3

db/migrate/20160220174777_add_status_stat_foreign_key.rb

@@ -0,0 +1,16 @@
+# db/migrate/[timestamp]_add_status_stat_foreign_key.rb
+class AddStatusStatForeignKey < ActiveRecord::Migration[8.0]
+    disable_ddl_transaction!
+  
+    def up
+      add_foreign_key :statuses, :status_stats,
+                     validate: false # Important for large tables
+                     
+      # Validate in background
+      execute("ALTER TABLE statuses VALIDATE CONSTRAINT fk_rails_[constraint_name]")
+    end
+  
+    def down
+      remove_foreign_key :statuses, :status_stats
+    end
+  end