> would we add another constant like private $commitTextFalse = 'softCommit=false'; ?

not needed, empty string means no commit asked by [solr](http://wiki.apache.org/solr/UpdateXmlMessages#A.22commit.22_and_.22optimize.22).

> constant with a different value than we use in the "default" 
It's not a constant.

This is a POC, me or @pspanja will do another round on this later this week and ask for feedback when it is actually ready for review ;)