Some links
- https://confluence.sakaiproject.org/display/SEARCH/IndexClusterOperation
- https://stackoverflow.com/questions/11450416/incremental-indexing-lucene
- https://rahuldausa.wordpress.com/2013/01/14/scaling-lucene-for-indexing-a-billion-documents/
- http://docs.hazelcast.org/docs/latest/manual/html/map-persistence.html
- https://lucidworks.com/blog/2009/09/02/scaling-lucene-and-solr/