I recently found a very neat plugin called Query Reviewer for visualizing slow sql queries in your rails app. When I installed it, I saw this error message

NoMethodError: undefined method `silence‘ for #<Log4r::Logger:0×39593f8>

You will see this error if you are using log4r for logging instead of the default rails logger. This ticket also talks of the same error in a different scenario. To fix the issue, edit the file vendor/plugins/query_reviewer/lib/query_reviewer/mysql_adapter_extensions.rb and replace all instance of @logger.silence with ActiveRecord::Base.silence.