The packed int4 Lucene99 scalar-quantized supplier scorer overwrites the score correction cached for its scoring ordinal on a cache miss, so score(i) depends on earlier score() calls; on the released 10.2.x/10.3.x a forceMerge of such a field builds a different HNSW graph, and on main and 10.4+ only internal callers reach it (known: open PR #16830)

Finding LFV-1105Area: codecs / backward-codecs Lucene99 scalar-quantized vectors (OffHeapQuantizedByteVectorValues)Priority: lowImpact: minorNovelty: known upstream

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

What it shows

With the packed int4 Lucene99 supplier scorer and scoring ordinal 1, score(1) should be the same before and after score(0); it is 0.99679184 before and 0.91709924 after, because getScoreCorrectionConstant(0) on a cache miss overwrites the correction cached for lastOrd. In 10.2.x/10.3.x graph building goes through this scorer, so a forceMerge of a compress=true 4-bit field builds a different graph; searches are not affected.

Expected vs actual

Expected: The test passes: it asserts the documented behaviour.
Actual: While the reported behaviour is present the test fails; the failure message states expected against actual.

Files

src/org/apache/lucene/backward_codecs/lucene99/TestPackedInt4SupplierStaleCorrection.java (JUnit test)

Run it

Tested on Lucene main e1faeba08bde (2026-11-02): reproduced.
Tested on Lucene main 645d4fe14a20 (2026-10-28): reproduced.
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=$CP:$LUCENE/lucene/backward-codecs/build/libs/lucene-backward-codecs-$V.jar
CP=$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 -XX:ActiveProcessorCount=2 -Dtests.seed=DEADBEEF \
     -cp "classes:$CP" org.junit.platform.console.ConsoleLauncher \
     execute --select-class org.apache.lucene.backward_codecs.lucene99.TestPackedInt4SupplierStaleCorrection

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 2026-11-03. AI-assisted; not yet triaged by a human Lucene committer. Feedback: open an issue in lucene-ai-bug-hunt.