group member count optimization

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 2019_07_21_234917) do
+ActiveRecord::Schema.define(version: 2019_07_22_003649) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -358,6 +358,7 @@ ActiveRecord::Schema.define(version: 2019_07_21_234917) do
     t.boolean "is_archived", default: false, null: false
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
+    t.integer "member_count", default: 0
     t.index ["account_id"], name: "index_groups_on_account_id"
   end