A float vector field routed to HnswBitVectorsFormat is rejected inside an aborting step of the indexing chain, so the one rejected document closes the IndexWriter and rolls back every document added since the last commit

Finding LFV-121Area: codecs / HnswBitVectorsFormat x index / IndexingChain aborting-exception classificationPriority: lowImpact: crashNovelty: new

Finding page for LFV-121

AI-assisted finding, confirmed by automated checks, not yet triaged by a human Lucene committer. This site files nothing upstream.

What it shows

You use HnswBitVectorsFormat, which accepts only byte vectors, and by mistake add a document with a float vector field (KnnFloatVectorField) that is new to the index. You expect addDocument to reject that one document with IllegalArgumentException and the writer to stay open, as the format's own test TestHnswBitVectorsFormat#testFloatVectorFails expects the exception and as happens for the same codec's dimension limit and for a vector dimension mismatch. Instead the check sits in KnnVectorsWriter#addField, which IndexingChain calls after registering the field and treats as an aborting step, so the exception also becomes the writer's tragic exception: IndexWriter closes itself, the next call throws AlreadyClosedException, and the documents added since the last commit are gone (the repro ends with 1 committed document instead of 3).

The test shows that with HnswBitVectorsFormat (byte vectors only), addDocument of one KnnFloatVectorField throws the expected IllegalArgumentException, but the same exception also becomes the IndexWriter's tragic exception, so the writer closes itself (and drops everything since the last commit).

Expected vs actual

Expected getTragicException() to be null after the rejected document; actual: IllegalArgumentException: HnswBitVectorsFormat only supports BYTE encoding, with -ea and -da.

Files

• src/org/apache/lucene/codecs/bitvectors/TestBitVectorsRejectedFloatField.java (JUnit test)

Run it

• Tested on Lucene main e1faeba08bde (2026-11-02): still reproduces.
• Tested on Lucene main 645d4fe14a20 (2026-10-28): reproduced.
• Recorded outcome of run 1 on Lucene main 645d4fe14a20: 1 test(s) run, 1 failed.
• How to read the outcome: a failing test is the finding reproducing (the failure message states expected against actual).
• Seeds: a rerun with the same seed replays the same random choices. Assertions off (-da -dsa -Dtests.asserts=false) is the production-like setting.

# Lucene checkout at the tested commit, built with: ./gradlew --no-daemon assemble   (JDK 25)
LUCENE=/path/to/lucene; V=12.0.0-SNAPSHOT
CP=$LUCENE/lucene/core/build/libs/lucene-core-$V.jar
CP=$CP:$LUCENE/lucene/codecs/build/libs/lucene-codecs-$V.jar
CP=$CP:$LUCENE/lucene/test-framework/build/libs/lucene-test-framework-$V.jar
CP=$CP:randomizedtesting-runner-2.9.2.jar:junit-4.13.2.jar:hamcrest-3.0.jar   # test-framework dependencies (Maven Central)
CP=$CP:junit-platform-console-standalone-6.1.3.jar   # JUnit Platform console launcher (Maven Central)

javac -d classes -cp "$CP" $(find src -name '*.java')

# run 1: assertions on, seed DEADBEEF
java -ea -esa --add-modules jdk.incubator.vector --enable-native-access=ALL-UNNAMED -Dtests.seed=DEADBEEF \
     -cp "classes:$CP" org.junit.platform.console.ConsoleLauncher \
     execute --select-class org.apache.lucene.codecs.bitvectors.TestBitVectorsRejectedFloatField

Gradle alternative: copy the test into the matching module's src/test/ tree of the checkout and run ./gradlew -p lucene/<module> test --tests <class> -Ptests.seed=<seed> (add -Ptests.asserts=false for a run without assertions).

Feedback

Open an issue in lucene-ai-bug-hunt. Please do not open issues or pull requests in apache/lucene about this finding unless a Lucene committer agrees it should be filed.

Snapshot of 2026-11-04. AI-assisted; not yet triaged by a human Lucene committer. Feedback: open an issue in lucene-ai-bug-hunt.