afs commented on issue #3488:
URL: https://github.com/apache/jena/issues/3488#issuecomment-3384750087

   > The `--add-modules=jdk.incubator.vector` was only added when we upgraded 
from 5.2.0 to 5.5.0.
   > This problem was also happening already before that (though less 
frequently) on 5.2.0 and without `--add-modules=jdk.incubator.vector`, so I 
don't think it is the root cause.
   
   Agreed - it's not the cause of compaction getting stuck. This is just trying 
to simplify the problem space.
   
   Is the `java.lang.InternalError` new at 5.5.0 or was it occurring for 5.2.0?
   
   `java.lang.InternalError` is coming from inside the JVM. Either some 
external process is affecting the memory mapped files, or an unrelated error 
JVM-internal has occurred and this is a symptom later. `jdk.incubator.vector` 
support in Lucene is quite new and I believe experimental - it also depends on 
the underlying hardware capabilities.
   
   Lucene itself is capable of using memory mapped files.
   
   ```
   INFO: Using MemorySegmentIndexInput and native madvise support with Java 21 
or later; to disable start with 
-Dorg.apache.lucene.store.MMapDirectory.enableMemorySegments=false
   ```
   Jena is shipping with Lucene9 because Lucene10 requires Java21; Jena 
supports Java17 until the upcoming Jena 6.0.0.
   
   tl;dr: Lucene is complicated!
   


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