Hey, you should compare with the ThreadedIndexWriter too :). I'll attach the source from Lucene in action SE manual and you can just replace the new IntexWriter(... with new ThreadedIndexWriter(...

See if those results make a difference. Also I presume you don't have a single core cpu

2011/10/11 Marc Sturlese <marc.sturlese@gmail.com>
I'm doing some performance test doing bulk indexing with lucene 4.0