Monitor.register with the same query id twice in one call keeps both versions in the query index, so the query matches a mix of both versions, and after a reopen a persistent Monitor runs the older version while getQuery returns the newer one

Finding LFV-332Area: monitor / query index updates (WritableQueryIndex.commitWithoutNotify and populateQueryCache, reached through both Monitor.register overloads and ConcurrentQueryLoader)Priority: lowImpact: silent wrong resultsNovelty: new

Finding page for LFV-332

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 query id q twice in one call, monitor.register(List.of(new MonitorQuery("q", apple OR banana), new MonitorQuery("q", cherry))), as an application might when it applies a batch of query edits, and expect q to behave like one version, as it does when the two entries are registered in separate calls (the newer replaces the older). Instead the query index keeps both versions: q is reported for documents containing banana or cherry, a set that neither version matches, and getDisjunctCount is 3 for a one-clause query. With a persistent Monitor (q = apple, then q = cherry, in one call) the newer version runs until the Monitor is reopened, and from then on the older version apple runs instead while getQuery("q") still returns cherry.

The test shows that registering two versions of query id q in one Monitor.register call keeps parts of both versions, so q matches like neither of them.

Expected vs actual

Expected q to match like one version, [apple, banana] or [cherry]; actual [banana, cherry], with -ea and -da.

Files

• src/org/apache/lucene/monitor/TestRegisterDuplicateIdInOneCall.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.TestRegisterDuplicateIdInOneCall

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-presearcher

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.