'HotSpot ' ?

A fabulous online content for Java performance tuning from Sun's site:
http://java.sun.com/docs/books/performance/ 1st_edition/html/JPTOC.fm.html

Also, more on the term 'HotSpot':
http://java.sun.com/docs/books/performance/1st_edition/html/JPAppHotspot.fm.html#997350