The Apache Lucene community has just released Lucene 3.4.0 and Solr 3.4.0.

You can read the official announcements here and here.

There are several juicy additions, but also a critical bug fix.  It is recommended that all 3.x-using applications upgrade to 3.4 as soon as possible.  Here’s the scoop on this fixed bug:

* Fixed a major bug (LUCENE-3418) whereby a Lucene index could
  easily become corrupted if the OS or computer crashed or lost

Lucene 3.4.0 includes:  a new faceting module (contrib/facet) for computing facet counts (both hierarchical and non-hierarchical) at search time (LUCENE-3079);  a new join module (contrib/join), enabling indexing and searching of nested (parent/child) documents using  (LUCENE-3171);  ability to now to index documents with term frequencies included but without positions (LUCENE-2048) – previously omitTermFreqAndPositions always omitted both; and a few other improvements.

Solr 3.4.0 includes: Lucene 3.4.0, which fixes the serious bug mentioned above; a new XsltUpdateRequestHandler allows posting XML that’s transformed by a provided XSLT into a valid Solr document (SOLR-2630); field grouping/collapsing: post-group faceting option (group.truncate) can now compute facet counts for only the highest ranking documents per-group (SOLR-2665); The query cache and filter cache can now be disabled per request (SOLR-2429); Improved memory usage, build time, and performance of SynonymFilterFactory (LUCENE-3233); various fixes for multi-threaded DataImportHandler; and a few other improvements.

Here are the links for more information and download access: Lucene 3.4.0 and Solr 3.4.0