IndexWriter#addBatch marks the frozen FieldType of an earlier rejected document as validated, so later documents with that type skip the per-field schema check (a wrong-dimension vector is stored truncated)

Finding LFV-127Area: index / IndexingChain per-field schema validation (frozen-FieldType cache) x columnar addBatchPriority: lowImpact: silent wrong resultsNovelty: new

Finding page for LFV-127

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

What it shows

You add a document whose 8-dimensional KnnFloatVectorField (built from one shared frozen FieldType) does not match the field's 4 dimensions, and Lucene correctly rejects it; you then index an IndexWriter#addBatch with a 4-dimensional vector column for the same field and add the same kind of 8-dimensional document again. You expect the same IllegalArgumentException, because Lucene requires a field to keep the same data structures in every document and checks each document against them. Instead the batch marks the rejected document's FieldType as already validated, so until the next flush every document with that FieldType instance skips the check: the 8-dimensional vector is accepted and stored as its first 4 values (CheckIndex clean), and a SORTED value for a NUMERIC doc-values field fails with ClassCastException instead of the schema error.

The test shows that after a document with an 8-dim KnnFloatVectorField (one frozen FieldType) is rejected on a 4-dim field, an IndexWriter#addBatch with a 4-dim vector column for that field makes the writer accept the same 8-dim document (its vector is stored truncated to 4 values).

Expected vs actual

Expected IllegalArgumentException on the second add, as on the first; actual: Expected exception IllegalArgumentException but no exception was thrown, with -ea and -da.

Files

• src/org/apache/lucene/index/TestAddBatchRejectedFrozenType.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.index.TestAddBatchRejectedFrozenType

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).

Formal models and scripts this finding's part of the hunt used: indexingchain-schema

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.