When deugging and troubleshooting, it is quite helpful to see if Solr is performing well or not.
A useful number, but hard to get at, is the solr response time.
Current Jetty config logs in NCSA common format, but it is quite easy to append to it the response time: see http://dsharpdotnet.wordpress.com/2012/08/11/monitoring-latency-in-jettys-request-log/