For vector search in Lucene, functionality for memory access (on/off-heap -- using Panama FFM) and vectorization (using the Vector API -- jdk.incubator.vector) is tightly coupled (see PanamaVectorUtilSupport <https://github.com/apache/lucene/blob/602bfbd9af0ee9027de45c1572527eee6b073841/lucene/core/src/java25/org/apache/lucene/internal/vectorization/PanamaVectorUtilSupport.java#L57> ). This made sense when it was originally added, because Panama FFM was in preview + Vector API was incubating.
However, since Panama FFM was finalized in JDK22 ( https://openjdk.org/jeps/454), I wonder if we should decouple it from vectorization now? This would mean exposing (and supporting!) top-level on/off-heap vector similarity functions from all VectorUtilSupport <https://github.com/apache/lucene/blob/8f68736e75609d13053420450ad451e52cba107d/lucene/core/src/java/org/apache/lucene/internal/vectorization/VectorUtilSupport.java#L25> implementations (with Lucene providing one non-vectorized <https://github.com/apache/lucene/blob/8f68736e75609d13053420450ad451e52cba107d/lucene/core/src/java/org/apache/lucene/internal/vectorization/DefaultVectorUtilSupport.java#L26> and another Vector API powered vectorized <https://github.com/apache/lucene/blob/8f68736e75609d13053420450ad451e52cba107d/lucene/core/src/java25/org/apache/lucene/internal/vectorization/PanamaVectorUtilSupport.java#L57> implementation), and only scoping non-finalized (i.e. incubating Vector API related) functionality in the MR-JAR (i.e. java25/ <https://github.com/apache/lucene/tree/main/lucene/core/src/java25>) Although not a huge motivation, this would allow users that do not use vectorization to score vectors off-heap. The main benefit could be cleaner separation of functionality in the long term, also making it easier to write new VectorUtilSupport <https://github.com/apache/lucene/blob/8f68736e75609d13053420450ad451e52cba107d/lucene/core/src/java/org/apache/lucene/internal/vectorization/VectorUtilSupport.java#L25> implementations that primarily work with MemorySegment APIs (for example a native implementation in # <https://github.com/apache/lucene/pull/13572>13572 <https://github.com/apache/lucene/pull/13572>) Issue: https://github.com/apache/lucene/issues/15284 PR: https://github.com/apache/lucene/pull/15285 - Kaival
