Sequential DrillSideways never returns on a segment of more than 2^31 - 2048 documents: DrillSidewaysScorer's int chunk start wraps to Integer.MIN_VALUE, so its union and drill-down-advance loops never exit (released since 4.2.0)
Finding LFV-383Area: facet / DrillSideways (sequential DrillSidewaysScorer, union and drill-down-advance strategies)Priority: lowImpact: hangNovelty: new
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 faceted DrillSideways search in the default sequential mode on an index whose single segment holds more than 2,147,481,600 documents, which IndexWriter accepts (MAX_DOCS = 2,147,483,519), and expect it to return its hits as it does on a segment 2,048 documents smaller. Instead DrillSidewaysScorer's union and drill-down-advance loops walk the segment in 2048-document chunks with an int nextChunkStart that wraps from 2^31 - 2048 to Integer.MIN_VALUE before the exit test 'nextChunkStart >= maxDoc' can fire, so the search thread spins forever and the hits of the last chunk are never collected. Through the public API on a real segment of MAX_DOCS documents the stock search did not return within 300 s, while the fixed build returned its 3 hits in 0.033 s.
The test shows that DrillSidewaysScorer's union loop on a segment of IndexWriter.MAX_DOCS documents (simulated: a FilterLeafReader reports that maxDoc()) never ends, because the int chunk start wraps from 2^31 - 2048 to Integer.MIN_VALUE; the test's base iterator stops it after twice the 2^20 chunks.
Expected vs actual
Expected score() to return and collect the last 3 docs; actual AssertionError: ... still looping after 2097153 docID() calls, collected [], with -ea and -da.
Files
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=$CP:$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.TestDrillSidewaysScorerLastChunkThe 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).
Formal models and scripts this finding's part of the hunt used: overflow-at-scale-2
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.