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  • Support for indexing high-cardinality dimensionality numeric vectors to perform nearest-neighbor search, using the Hierarchical Navigable Small World graph algorithm.

File formats

  • File formats have all been changed from big-endian order to little endian order.

Optimizations

Optimizations

  • 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 new opt-out as of 9.0
  • Lucene 9 takes advantage of Java VarHandles, introduced in Java 9, to speed up indexing and some queries.
  • Lucene now enforces that a field has the same schema across all documents in order to enable optimizations that take advantage of the index by default.
  • ConcurrentMergeScheduler now assumes fast I/O, likely improving indexing speed in case where heuristics would incorrectly detect whether the system had fast modern I/O or not.
  • Encoding of postings lists changed from FOR-delta to PFOR-delta to save further disk space.

Other

  • File formats have all been changed from big-endian order to little endian order. 
  • Lucene 9 now 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. See https

Further details of changes are available in the change log available at: http://lucene.apache.org/core/9_0

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/changes/

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Changes.html

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

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

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