Add uniq_ip_or_user_id_topic_views index concurrently.

db/migrate/20180521175611_change_indexes_topic_view_item.rb

@@ -11,13 +11,11 @@ class ChangeIndexesTopicViewItem < ActiveRecord::Migration[5.1]
       column: [:ip_address, :topic_id],
       name: :ip_address_topic_id_topic_views,
       unique: true
+
     remove_index :topic_views,
       column: [:user_id, :topic_id],
       name: :user_id_topic_id_topic_views,
       unique: true
-    add_index :topic_views, [:user_id, :ip_address, :topic_id],
-      name: :uniq_ip_or_user_id_topic_views,
-      unique: true
   end
 
   def down

db/migrate/20180716140323_add_uniq_ip_or_user_id_topic_views.rb

@@ -0,0 +1,15 @@
+class AddUniqIpOrUserIdTopicViews < ActiveRecord::Migration[5.2]
+  disable_ddl_transaction!
+
+  def change
+    unless index_exists?(:topic_views, [:user_id, :ip_address, :topic_id],
+      name: :uniq_ip_or_user_id_topic_views
+    )
+
+      add_index :topic_views, [:user_id, :ip_address, :topic_id],
+        name: :uniq_ip_or_user_id_topic_views,
+        unique: true,
+        algorithm: :concurrently
+    end
+  end
+end