This is a ticket to integrate learning to rank machine learning models into Solr. Solr Learning to Rank (LTR) provides a way for you to extract features directly inside Solr for use in training a machine learned model. You can then deploy that model to Solr and use it to rerank your top X search results. This concept was previously presented by the authors at Lucene/Solr Revolution 2015.
Solr Reference Guide documentation:
Source code and README files: