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System requirements
- Lucene 10.0 requires JDK 21 or newer
API changes
- KNN vector values now have a random-access API.
- Deprecated APIs have been removed and a number of API changes have been made. Please consult the migrate guide for an extensive list and actions to take to migrate to 10.0.
New Features
- A new IndexInput#prefetch API has been added, allowing query evaluation logic to let the Directory know about regions of data that are about to be read. This helps perform I/O concurrently under the hood. MMapDirectory implements this API using the madvise system call and the MADV_WILLNEED flag on Linux and Mac OS.
- Lucene now supports sparse indexing on doc values via FieldType#setDocValuesSkipIndexType. The sparse index will record the minimum and maximum values per block of doc IDs. Used in conjunction with index sorting to cluster similar documents together, this allows for very space-efficient and CPU-efficient filtering.
- Search concurrency is now decoupled from the index geometry, so that an index can be searched using any number of threads, regardless of its number of segments.
- Kmeans clustering on vectors
Improvements
- Lucene now opens files with the MADV_RANDOM advice by default on Linux and Mac OS. This results in better efficiency for indexes that exceed the size of the page cache, but can make it slower to load indexes in the page cache. It is possible to revert to the MADV_NORMAL read advice by default by passing -Dorg.apache.lucene.store.defaultReadAdvice=NORMAL as a JVM startup flag.
- Snowball dictionaries have been upgraded, resulting in improved tokenization. This may require reindexing to ensure consistency of search results with pre-10.0 indexes.
- The expressions module is now using MethodHandles and Dynamic Class-File Constants (JEP 309) in combination with hidden classes (JEP 371) to implement a strict and type-safe call to external functions. This allows to easier extend expressions with custom functions in secure way because runtime linking of custom functions is no longer the responsibility of the expressions scripting engine. In addition, the hidden classes created by the expressions engine no longer suffer from global classloader locks.
... plus a multitude of helpful bug fixes!