Do you have a rails app with a lot of callbacks? Are they kind of a mystery? Maybe logging them would help.
Started GET "/" for 127.0.0.1 at 2016-07-26 13:25:32 -0400 Processing by HomeController#index as HTML Callback: verify_authenticity_token Callback: activate_authlogic Callback: require_client_subdomain Client Load (0.4ms) SELECT `clients`.* ... Callback: check_hostname Callback: update_last_request_at ...
# Gemfile gem "rails-callback_log", group: [:development, :test]
Do not use this gem in production because it adds significant overhead.
Rails has a lot of its own callbacks that you probably don't care about. If you don't want to log them, enable filtering.
# Enable filtering export RAILS_CALLBACK_LOG_FILTER="make it so" # Disable filtering unset RAILS_CALLBACK_LOG_FILTER
Filtering incurs a serious performance penalty, so it is off by default.
The gem is available as open source under the terms of the MIT License.