rails s 之后，出现了 auto_explain_threshold_in_seconds is set but will be ignored...的警告，如何解决呢。警告的意思是什么呢。一般程序中设置 auto_explain_threshold_in_seconds 是来做什么的？

$rails s => Booting WEBrick => Rails 3.2.13 application starting in development on http://0.0.0.0:3000 => Call with -d to detach => Ctrl-C to shutdown server auto_explain_threshold_in_seconds is set but will be ignored because your adapter does not support this feature. Please unset the configuration to avoid this warning. [2013-06-09 21:06:37] INFO WEBrick 1.3.1 [2013-06-09 21:06:37] INFO ruby 1.9.2 (2012-04-20) [i686-linux] [2013-06-09 21:06:37] INFO WEBrick::HTTPServer#start: pid=11753 port=3000