Sequential DrillSideways lets a TOP_SCORES hit collector prune the shared base query, so drill-sideways facet counts silently miss matching documents

Finding LFV-789Area: facet / DrillSideways (sequential query-first scoring: score mode of the base weight and the scorable handed to the hit collector)Priority: mediumImpact: silent wrong resultsNovelty: new

Finding page for LFV-789

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

What it shows

You run a sequential DrillSideways search (no executor) with a filter-style base query drilled down to color=red, and pass a TopScoreDocCollectorManager with a finite total-hits threshold (10 in the repro, or IndexSearcher's default 1000) as the hit collector through search(DrillDownQuery, CollectorManager, List). You expect the drill-sideways counts for color to include every document that matches the base query (75 in the repro), as the same search does with an exhaustive hit collector or with the concurrent DrillSideways. Instead the counts are silently too low (11, or 1001 instead of 2250 at threshold 1000): the base query is scored with the hit collector's TOP_SCORES mode and its scorer is handed to the hit collector, whose min-competitive-score updates make the shared base iteration skip documents that the sideways collectors then never see; the top hits are correct.

Expected vs actual

Expected: The sideways color counts include every shoe: red 75, blue 75.
Actual: ComparisonFailure: sideways color counts red/blue expected:<[75/75]> but was:<[11/10]>.

Files

src/org/apache/lucene/facet/TestDrillSidewaysTopScoresCollector.java (JUnit test)
src/org/apache/lucene/facet/TestDrillSidewaysTopScoresTwoArgSearch.java (JUnit test)

Run it

Tested on Lucene main e1faeba08bde (2026-11-02): still reproduces.
Tested on Lucene main a9779ef3c193 (2026-10-26): 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/facet/build/libs/lucene-facet-$V.jar
CP=$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.facet.TestDrillSidewaysTopScoresCollector

# run 2: assertions on, seed DEADBEEF, default flags
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.facet.TestDrillSidewaysTopScoresTwoArgSearch

The module(s) facet also need their third-party runtime jars; ./gradlew -p lucene/<module> dependencies lists them.

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).

Files shown on the finding page

TestDrillSidewaysTopScoresHitCollector.java

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.