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From: Robert Muir <[email protected]> Subject: [ANNOUNCE] Apache Lucene 4.0-alpha released. Date: July 3, 2012 3:09:13 PM GMT+02:00 To: [email protected], Lucene mailing list <[email protected]>, java-user <[email protected]>, announce <[email protected]>

3 July 2012, Apache Lucene‚ 4.0-alpha available The Lucene PMC is pleased to announce the release of Apache Lucene 4.0-alpha

Apache Lucene is a high-performance, full-featured text search engine library written entirely in Java. It is a technology suitable for nearly any application that requires full-text search, especially cross-platform.

This release contains numerous bug fixes, optimizations, and improvements, some of which are highlighted below. The release is available for immediate download at: http://lucene.apache.org/core/mirrors-core-latest-redir.html?ver=4.0a

See the CHANGES.txt file included with the release for a full list of details.

Lucene 4.0-alpha Release Highlights:

* The index formats for terms, postings lists, stored fields, term vectors, etc are pluggable via the Codec api. You can select from the provided implementations or customize the index format with your own Codec to meet your needs.

* Similarity has been decoupled from the vector space model (TF/IDF). Additional models such as BM25, Divergence from Randomness, Language Models, and Information-based models are provided (see http://www.lucidimagination.com/blog/2011/09/12/flexible-ranking-in-lucene-4).

* Added support for per-document values (DocValues). DocValues can be used for custom scoring factors (accessible via Similarity), for pre-sorted Sort values, and more.

* When indexing via multiple threads, each IndexWriter thread now flushes its own segment to disk concurrently, resulting in substantial performance improvements (see http://blog.mikemccandless.com/2011/05/265-indexing-speedup-with-lucenes.htm...).

* Per-document normalization factors ("norms") are no longer limited to a single byte. Similarity implementations can use any DocValues type to store norms.

* Added index statistics such as the number of tokens for a term or field, number of postings for a field, and number of documents with a posting for a field: these support additional scoring models (see http://blog.mikemccandless.com/2012/03/new-index-statistics-in-lucene-40.htm...).

* Implemented a new default term dictionary/index (BlockTree) that indexes shared prefixes instead of every n'th term. This is not only more time- and space- efficient, but can also sometimes avoid going to disk at all for terms that do not exist. Alternative term dictionary implementions are provided and pluggable via the Codec api.

* Indexed terms are no longer UTF-16 char sequences, instead terms can be any binary value encoded as byte arrays. By default, text terms are now encoded as UTF-8 bytes. Sort order of terms is now defined by their binary value, which is identical to UTF-8 sort order.

* Substantially faster performance when using a Filter during searching.

* File-system based directories can rate-limit the IO (MB/sec) of merge threads, to reduce IO contention between merging and searching threads.

* Added a number of alternative Codecs and components for different use-cases: "Appending" works with append-only filesystems (such as Hadoop DFS), "Memory" writes the entire terms+postings as an FST read into RAM (see http://blog.mikemccandless.com/2011/06/primary-key-lookups-are-28x-faster-wi...), "Pulsing" inlines the postings for low-frequency terms into the term dictionary (see http://blog.mikemccandless.com/2010/06/lucenes-pulsingcodec-on-primary-key.h...), "SimpleText" writes all files in plain-text for easy debugging/transparency (see http://blog.mikemccandless.com/2010/10/lucenes-simpletext-codec.html), among others.

* Term offsets can be optionally encoded into the postings lists and can be retrieved per-position.

* A new AutomatonQuery returns all documents containing any term matching a provided finite-state automaton (see http://www.slideshare.net/otisg/finite-state-queries-in-lucene).

* FuzzyQuery is 100-200 times faster than in past releases (see http://blog.mikemccandless.com/2011/03/lucenes-fuzzyquery-is-100-times-faste...).

* A new spell checker, DirectSpellChecker, finds possible corrections directly against the main search index without requiring a separate index.

* Various in-memory data structures such as the term dictionary and FieldCache are represented more efficiently with less object overhead (see http://blog.mikemccandless.com/2010/07/lucenes-ram-usage-for-searching.html).

* All search logic is now required to work per segment, IndexReader was therefore refactored to differentiate between atomic and composite readers (see http://blog.thetaphi.de/2012/02/is-your-indexreader-atomic-major.html).

* Lucene 4.0 provides a modular API, consolidating components such as Analyzers and Queries that were previously scattered across Lucene core, contrib, and Solr. These modules also include additional functionality such as UIMA analyzer integration and a completely reworked spatial search implementation.

Please read CHANGES.txt and MIGRATE.txt for a full list of new features and notes on upgrading. Particularly, the new apis are not compatible with previous version of Lucene, however, file format backwards compatibility is provided for indexes from the 3.0 series.

This is an alpha release for early adopters. The guarantee for this alpha release is that the index format will be the 4.0 index format, supported through the 5.x series of Apache Lucene, unless there is a critical bug (e.g. that would cause index corruption) that would prevent this.

Please report any feedback to the mailing lists (http://lucene.apache.org/core/discussion.html)

Happy searching,

Apache Lucene/Solr Developers