Requests got stuck in ActiveRecord::QueryCache middleware

Question

After deploying our Rails app (4.0.9, Ruby 2.1.2), we notice requests to our app get hang after a while , usually 1 day or so.

Using the gem rack_timer, we

Answer 1

The most possible cause is your connection with the database died (firewall, server configuration...) and Rails didn't notice, so a timeout happens inside ActiveRecord::QueryCache. Once Rails notices the connection died, it reconnects and the execution flow continues.

Try setting the param read_timeout in your database.yml file to something like 10 seconds and check your connection and server settings.