Github user rvesse commented on the issue:
https://github.com/apache/jena/pull/297
Parallelism of 2 gives similar benefits. I have a quad core machine
personally.
One possible approach is to use the `build-helper:cpu-count` plugin -
http://www.mojohaus.org/build-helper-maven-plugin/cpu-count-mojo.html - to
dynamically set the level of parallelism so that we don't over subscribe the
users system---
