"Lucene enhancements include the addition of a
suggest/auto-complete function in the spell checker module, a less
aggressive stemmer for English called KStem and the ability to
merge results from multiple shards.
"Solr sees improvements which make use of the Lucene
enhancements with a KStemFilterFactory, new suggest/autocomplete
implementation "offering an order of magnitude smaller RAM
consumption" and a new, more efficient merge policy used by