Apache Solr – Grouping update
Apache Solr’s result grouping feature is now a widely used feature. The major drawback was that grouping (also known as sharding in Solr) was initially not supported for distributed searches. The good news is that recently distributed grouping has been added to Solr! It has been added as the trunk and the stable branch (branch3x). This means that distributed grouping will be included in the upcoming Solr 3.5 and Solr 4.0 release.