XX Dec 2023, Apache Lucene™ 9.9.0 available

<work in progress>

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

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 patch release contains bug fixes that are highlighted below. The release is available for immediate download at:

http://lucene.apache.org/core/mirrors-core-latest-redir.html

Lucene 9.0.0 Release Highlights

API Changes

• Make TaskExecutor constructor public and use TaskExecutor for concurrent HNSW graph build. (Shubham Chaudhary)

New Features

• Add int8 scalar quantization to the HNSW vector format. This optionally allows for more compact lossy storage for the vectors, requiring about 75% memory for fast HNSW search.
• HNSW graph now can be merged with multiple thread.

Improvements

• Create a TaskExecutor when an executor is not provided to the IndexSearcher, in order to simplify consumer's code 
• 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.

Further details of changes are available in the change log available at: http://lucene.apache.org/core/9_9_0/changes/Changes.html

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

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