[ANNOUNCE] Apache Lucene 9.9.0 released

[Chris Hegarty <ch...@elastic.co.INVALID>]

The Lucene PMC is pleased to announce the release of Apache Lucene 9.9.0.

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 bug fixes, optimizations, and improvements, some of which are highlighted below. The release is available for immediate download at:

https://lucene.apache.org/core/downloads.html

Lucene 9.9.0 Release Highlights:

New Features
    • Add int8 scalar quantization to the HNSW vector format. This optionally allows for more compact lossy storage for the vectors, requiring approximately 4x less memory for fast HNSW search.
    • HNSW graph now can be merged with multiple threads, leveraging the same infrastructure that inter-segment concurrency utilizes.

Improvements
    • Speed up Panama vector support, use FMA, and test improvements. 
    • FSTCompiler can now approximately limit how much RAM it uses to share suffixes during FST construction using the suffixRAMLimitMB method. 

Optimizations
    • Faster top-level conjunctions on term queries when sorting by descending score.
    • Change Postings back to using FOR in Lucene99PostingsFormat. Freqs, positions and offset keep using PFOR.

... plus a multitude of helpful bug fixes!

Please read CHANGES.txt for a full list of new features and changes:

https://lucene.apache.org/core/9_9_0/changes/Changes.html

-Chris.
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