ReqExclBulkScorer.WindowBits.applyMask adds offset + bitSet.length() in int, so FILTER/MUST + MUST_NOT queries silently drop every match in a 4096-doc window based at doc 2^31-4096 or above (up to the last 3,967 doc IDs of a segment near IndexWriter.MAX_DOCS)
Finding LFV-139Area: search / BooleanQuery MUST_NOT bulk scoring (ReqExclBulkScorer)Priority: lowImpact: silent wrong resultsNovelty: 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 index one segment of IndexWriter.MAX_DOCS (2,147,483,519) documents with default settings, one of which has b:y, and count the matches of +*:* -b:y (MatchAllDocsQuery as FILTER plus a MUST_NOT term query) with a plain IndexSearcher; you expect 2,147,483,518. Instead you get 2,147,479,551: all 3,967 documents of the last window [2,147,479,552, MAX_DOCS) are silently missing, because ReqExclBulkScorer's WindowBits.applyMask computes Math.min(NO_MORE_DOCS, offset + bitSet.length()) in int, the sum wraps negative for a 4096-bit window based at 2^31-4096 or above, and the method then clears the whole window. Only segments with more than 2,147,479,552 documents and required clauses denser than 0.3% of maxDoc are affected, and only code since #16669 has the bug: 10.6.0 (released 2026-10-29), main and branch_10x.
The test shows that ReqExclBulkScorer drops every match of a dense required clause in the 4096-doc window based at 2^31-4096 when a MUST_NOT clause is present, because WindowBits.applyMask adds offset + bitSet.length() in int (no index built).
Expected vs actual
Expected 99 hits (the last 100 doc IDs of a MAX_DOCS segment minus one excluded); actual 0 (expected:<99> but was:<0>), 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=$CP:randomizedtesting-runner-2.9.2.jar:junit-4.13.2.jar:hamcrest-3.0.jar # test-framework dependencies (Maven Central)
CP=$CP:junit-platform-console-standalone-6.1.3.jar # JUnit Platform console launcher (Maven Central)
javac -d classes -cp "$CP" $(find src -name '*.java')
# run 1: assertions on, seed DEADBEEF
java -ea -esa -Xmx2g --add-modules jdk.incubator.vector --enable-native-access=ALL-UNNAMED -Dtests.seed=DEADBEEF \
-cp "classes:$CP" org.junit.platform.console.ConsoleLauncher \
execute --select-class org.apache.lucene.search.TestReqExclLastWindowGradle 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: bitsets-livedocs-acceptdocs
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.