A Monitor.register call that IndexWriter rejects is not rolled back: the earlier versions of the queries in the call are deleted at the next commit or close(), and until then getQuery() and match() disagree
Finding LFV-499Area: monitor / query index updates (WritableQueryIndex.commitWithoutNotify failure atomicity, reached through both Monitor.register overloads)Priority: lowImpact: data corruptionNovelty: 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 update stored queries with Monitor.register and IndexWriter rejects one of the new query documents, for example register(q2 = f:y) where q2 carries a 40,000-byte value in a TermFilteredPresearcher filter field, so register() throws IllegalArgumentException. You expect the queries of the call to keep their old versions, as they do when the Monitor rejects a query before writing and as IndexWriter.updateDocuments would guarantee for each id. Instead the Monitor has already queued the deletion of the old version of every query id in the call and switched its in-memory cache to the new versions: right away q2 matches nothing although getQuery("q2") still returns f:b, and the next unrelated register or deleteById, or close() of a persistent Monitor, deletes the old versions for good (register(q2 rejected, q1 valid), then close and reopen, leaves neither q1 nor q2).
The test shows that a Monitor.register call that IndexWriter rejects (q2 carries a 40,000-byte filter-field value) still deletes another query of the same call, q1, once the on-disk Monitor is closed.
Expected vs actual
Expected q1 to still be registered after close and reopen ([q1]); actual: no queries (expected:<[q1]> but was:<[]>), 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/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.TestFailedRegisterDeletesOtherQueryGradle 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-lifecycle-persistence-mbt
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.