add mem cache in poduction.rb

config/environments/production.rb

@@ -57,7 +57,7 @@
   config.log_tags = [ :request_id ]
 
   # Use a different cache store in production.
-  # config.cache_store = :mem_cache_store
+  config.cache_store = :memory_store, { size: 64.megabytes }
 
   # Use a real queuing backend for Active Job (and separate queues per environment)
   # config.active_job.queue_adapter     = :resque