Lucene Monitor's QueryDecomposer collects a query's parts in a Set, so a sub-query that occurs more than once in a registered query (a repeated SHOULD or MUST clause, or a term shared by two nested disjunctions) is scored once by ScoringMatch and ExplainingMatch instead of once per occurrence

Finding LFV-856Area: monitor / query decomposition and match scoring (QueryDecomposer Set<Query> parts, ScoringMatch/ExplainingMatch resolve)Priority: lowImpact: silent wrong resultsNovelty: new

Finding page for LFV-856

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

What it shows

You register a query such as '(red apple) (green apple)' or 'apple apple' in a Monitor and match the document 'red green apple' with ScoringMatch or ExplainingMatch, expecting the score the query itself gives that document, which is what IndexSearcher returns, because BooleanQuery counts a repeated clause at every occurrence (0.5230583 and 0.26152915). Instead the Monitor reports 0.39229372 and 0.13076457: the default QueryDecomposer collects the query's parts in a Set, which keeps equal parts once, and the scoring matchers add up the scores of the distinct parts, so the shared 'apple' is counted once. Which queries match is not affected; only the scores and explanations of such queries are too low.

The test shows that Monitor's ScoringMatch scores the registered query (red apple) (green apple) on the document red green apple lower than IndexSearcher does, because QueryDecomposer's Set keeps the shared part apple once.

Expected vs actual

Expected: 0.5230583 (IndexSearcher's BM25 score of the same query on the same document). Actual: expected:<0.5230583> but was:<0.39229372>.

Files

• src/org/apache/lucene/monitor/TestMonitorSharedSubqueryScore.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=$CP:$LUCENE/lucene/analysis/common/build/libs/lucene-analysis-common-$V.jar
CP=$CP:$LUCENE/lucene/memory/build/libs/lucene-memory-$V.jar
CP=$CP:$LUCENE/lucene/monitor/build/libs/lucene-monitor-$V.jar
CP=$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.monitor.TestMonitorSharedSubqueryScore

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: monitor-matcher-agreement

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.