Nginx – Why is the Rails application hanging

I have a Rails application of moderate complexity running under Apache/Passenger which becomes unresponsive after periods of idleness. It takes several minutes to respond, but can be temporarily revived with a web server restart.

Server load is negligible, and since it's an internal application, there are rarely more than a few concurrent users.

I've tried nginx too, so it's not Apache causing the problem.

There isn't anything useful in the Apache or Rails logs. As per Passenger docs, I sent a SIGABRT and have a stacktrace (below). Its database isn't heavily loaded, and I've tried disabling any background processing which could be causing locks.

SignalException (SIGABRT):
  passenger (3.0.17) lib/phusion_passenger/abstract_request_handler.rb:443:in `block in install_useful_signal_handlers'
  activerecord (3.2.8) lib/active_record/connection_adapters/mysql2_adapter.rb:73:in `call'
  activerecord (3.2.8) lib/active_record/connection_adapters/mysql2_adapter.rb:73:in `ping'
  activerecord (3.2.8) lib/active_record/connection_adapters/mysql2_adapter.rb:73:in `active?'
  activerecord (3.2.8) lib/active_record/connection_adapters/abstract_adapter.rb:219:in `verify!'
  activerecord (3.2.8) lib/active_record/connection_adapters/abstract/connection_pool.rb:327:in `block in checkout_and_verify'
  activesupport (3.2.8) lib/active_support/callbacks.rb:403:in `_run__352340970312725798__checkout__1600727162984137669__callbacks'
  activesupport (3.2.8) lib/active_support/callbacks.rb:405:in `__run_callback'
  activesupport (3.2.8) lib/active_support/callbacks.rb:385:in `_run_checkout_callbacks'
  activesupport (3.2.8) lib/active_support/callbacks.rb:81:in `run_callbacks'
  activerecord (3.2.8) lib/active_record/connection_adapters/abstract/connection_pool.rb:326:in `checkout_and_verify'
  activerecord (3.2.8) lib/active_record/connection_adapters/abstract/connection_pool.rb:247:in `block (2 levels) in checkout'
  activerecord (3.2.8) lib/active_record/connection_adapters/abstract/connection_pool.rb:236:in `loop'
  activerecord (3.2.8) lib/active_record/connection_adapters/abstract/connection_pool.rb:236:in `block in checkout'
  /home/uuuuu/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/monitor.rb:211:in `mon_synchronize'
  activerecord (3.2.8) lib/active_record/connection_adapters/abstract/connection_pool.rb:233:in `checkout'
  activerecord (3.2.8) lib/active_record/connection_adapters/abstract/connection_pool.rb:96:in `block in connection'
  /home/uuuuu/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/monitor.rb:211:in `mon_synchronize'
  activerecord (3.2.8) lib/active_record/connection_adapters/abstract/connection_pool.rb:95:in `connection'
  activerecord (3.2.8) lib/active_record/connection_adapters/abstract/connection_pool.rb:404:in `retrieve_connection'
  activerecord (3.2.8) lib/active_record/connection_adapters/abstract/connection_specification.rb:170:in `retrieve_connection'
  activerecord (3.2.8) lib/active_record/connection_adapters/abstract/connection_specification.rb:144:in `connection'
  activerecord (3.2.8) lib/active_record/query_cache.rb:61:in `call'
  activerecord (3.2.8) lib/active_record/connection_adapters/abstract/connection_pool.rb:473:in `call'
  actionpack (3.2.8) lib/action_dispatch/middleware/callbacks.rb:28:in `block in call'
  activesupport (3.2.8) lib/active_support/callbacks.rb:405:in `_run__1086758471249540907__call__1600727162984137669__callbacks'
  activesupport (3.2.8) lib/active_support/callbacks.rb:405:in `__run_callback'
  activesupport (3.2.8) lib/active_support/callbacks.rb:385:in `_run_call_callbacks'
  activesupport (3.2.8) lib/active_support/callbacks.rb:81:in `run_callbacks'
  actionpack (3.2.8) lib/action_dispatch/middleware/callbacks.rb:27:in `call'
  actionpack (3.2.8) lib/action_dispatch/middleware/remote_ip.rb:31:in `call'
  actionpack (3.2.8) lib/action_dispatch/middleware/debug_exceptions.rb:16:in `call'
  actionpack (3.2.8) lib/action_dispatch/middleware/show_exceptions.rb:56:in `call'
  railties (3.2.8) lib/rails/rack/logger.rb:26:in `call_app'
  railties (3.2.8) lib/rails/rack/logger.rb:16:in `call'
  actionpack (3.2.8) lib/action_dispatch/middleware/request_id.rb:22:in `call'
  rack (1.4.1) lib/rack/methodoverride.rb:21:in `call'
  rack (1.4.1) lib/rack/runtime.rb:17:in `call'
  activesupport (3.2.8) lib/active_support/cache/strategy/local_cache.rb:72:in `call'
  rack (1.4.1) lib/rack/lock.rb:15:in `call'
  actionpack (3.2.8) lib/action_dispatch/middleware/static.rb:62:in `call'
  rack-cache (1.2) lib/rack/cache/context.rb:136:in `forward'
  rack-cache (1.2) lib/rack/cache/context.rb:245:in `fetch'
  rack-cache (1.2) lib/rack/cache/context.rb:185:in `lookup'
  rack-cache (1.2) lib/rack/cache/context.rb:66:in `call!'
  rack-cache (1.2) lib/rack/cache/context.rb:51:in `call'
  railties (3.2.8) lib/rails/engine.rb:479:in `call'
  railties (3.2.8) lib/rails/application.rb:223:in `call'
  railties (3.2.8) lib/rails/railtie/configurable.rb:30:in `method_missing'
  rack-pjax (0.6.0) lib/rack/pjax.rb:12:in `call'
  passenger (3.0.17) lib/phusion_passenger/rack/request_handler.rb:96:in `process_request'
  passenger (3.0.17) lib/phusion_passenger/abstract_request_handler.rb:516:in `accept_and_process_next_request'
  passenger (3.0.17) lib/phusion_passenger/abstract_request_handler.rb:274:in `main_loop'
  passenger (3.0.17) lib/phusion_passenger/rack/application_spawner.rb:206:in `start_request_handler'
  passenger (3.0.17) lib/phusion_passenger/rack/application_spawner.rb:171:in `block in handle_spawn_application'
  passenger (3.0.17) lib/phusion_passenger/utils.rb:470:in `safe_fork'
  passenger (3.0.17) lib/phusion_passenger/rack/application_spawner.rb:166:in `handle_spawn_application'
  passenger (3.0.17) lib/phusion_passenger/abstract_server.rb:357:in `server_main_loop'
  passenger (3.0.17) lib/phusion_passenger/abstract_server.rb:206:in `start_synchronously'
  passenger (3.0.17) lib/phusion_passenger/abstract_server.rb:180:in `start'
  passenger (3.0.17) lib/phusion_passenger/rack/application_spawner.rb:129:in `start'
  passenger (3.0.17) lib/phusion_passenger/spawn_manager.rb:253:in `block (2 levels) in spawn_rack_application'
  passenger (3.0.17) lib/phusion_passenger/abstract_server_collection.rb:132:in `lookup_or_add'
  passenger (3.0.17) lib/phusion_passenger/spawn_manager.rb:246:in `block in spawn_rack_application'
  passenger (3.0.17) lib/phusion_passenger/abstract_server_collection.rb:82:in `block in synchronize'
  :10:in `synchronize'
  passenger (3.0.17) lib/phusion_passenger/abstract_server_collection.rb:79:in `synchronize'
  passenger (3.0.17) lib/phusion_passenger/spawn_manager.rb:244:in `spawn_rack_application'
  passenger (3.0.17) lib/phusion_passenger/spawn_manager.rb:137:in `spawn_application'
  passenger (3.0.17) lib/phusion_passenger/spawn_manager.rb:275:in `handle_spawn_application'
  passenger (3.0.17) lib/phusion_passenger/abstract_server.rb:357:in `server_main_loop'
  passenger (3.0.17) lib/phusion_passenger/abstract_server.rb:206:in `start_synchronously'
  passenger (3.0.17) helper-scripts/passenger-spawn-server:99:in `'

database.yml:

production:
  adapter: mysql2
  encoding: utf8
  database: [db]
  host: [host]
  pool: 5
  username: [user]
  password: [pass]
  timeout: 2000

I'm running Ubuntu 12.04.1 LTS, Ruby 1.9.3p194 via RVM, and Passenger 3.0.18.

I've never experienced this issue in development mode under WEBrick.