Lucene Per-segment search
Per-segment searching is largely kept under the covers but since LexEVS employs a number of customizations of parameters, particularly filters many queries may break and need refactoring. At the same time a number of objects have new names, apis and other changes that will require refactoring and updating to an as yet undetermined amount.
The use of IndexReader in particular will not change, but filters and queries passed into this may break or otherwise be unusable. Read this article for more information: http://blog.thetaphi.de/2012/02/is-your-indexreader-atomic-major.html
Updated Objects will include
ChainedFilter replaced with BooleanFilter
HitCollector is replaced by Collector or SimpleCollector