07 December 2021, Apache Lucene™ 9.0 available

The Lucene PMC is pleased to announce the release of Apache Lucene 9.0.

Apache Lucene is a high-performance, full-featured search engine library written entirely in Java. It is a technology suitable for nearly any application that requires structured search, full-text search, faceting, nearest-neighbor search across high-dimensionality vectors, spell correction or query suggestions.

This release contains numerous features, optimizations, and improvements, some of which are highlighted below. The release is available for immediate download at:


Lucene 9.0 Release Highlights

System requirements

  • Lucene 9.0 requires JDK 11 or newer

New features

  • Support for indexing high-dimensionality numeric vectors to perform nearest-neighbor search, using the Hierarchical Navigable Small World graph algorithm
  • New Analyzers for Serbian, Nepali, and Tamil languages
  • IME-friendly autosuggest for Japanese
  • Snowball 2, adding Hindi, Indonesian, Nepali, Serbian, Tamil, and Yiddish stemmers
  • New normalization/stemming for Swedish and Norwegian


  • Up to 400% faster taxonomy faceting
  • 10-15% faster indexing of multi-dimensional points
  • Several times faster sorting on fields that are indexed with points. This optimization used to be an opt-in in late 8.x releases and is now opt-out as of 9.0.
  • ConcurrentMergeScheduler now assumes fast I/O, likely improving indexing speed in case where heuristics would incorrectly detect whether the system had modern I/O or not
  • Encoding of postings lists changed from FOR-delta to PFOR-delta to save further disk space


  • File formats have all been changed from big-endian order to little endian order
  • Lucene 9 no longer has split packages. This required renaming some packages outside of the lucene-core JAR, so you will need to adjust some imports accordingly.
  • Using Lucene 9 with the module system should be considered experimental. We expect to make progress on this in future 9.x releases.

Further details of changes are available in the change log available at: http://lucene.apache.org/core/9_0_0/changes/Changes.html and the migration guide available at https://lucene.apache.org/core/9_0_0/MIGRATE.html.

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

Note: The Apache Software Foundation now uses a content distribution network (CDN) for distributing releases.

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