http://blog.sina.com.cn/s/blog_539d361e0100xcy9.html
http://stackoverflow.com/questions/6923071/lucene-is-it-the-right-answer-for-huge-index
http://www.hpl.hp.com/techreports/2008/HPL-2008-64.html
http://www.gossamer-threads.com/lists/lucene/general/58087