CompletionScorer silently ignores the BulkScorer [min, max) window instead of rejecting it, so a CompletionQuery run through IndexSearcher#search with a timeout (even one that never fires) or with intra-segment partitions returns repeated suggestions and drops others
Finding LFV-969Area: suggest / document (NRT) suggester: CompletionScorer under IndexSearcher's windowed execution (setTimeout, intra-segment partitions)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 run a CompletionQuery through IndexSearcher#search with a TopSuggestDocsCollector (for example suggestSearcher.search(query, collector)) on a searcher that has a timeout set, even one that never fires, or that splits a segment into intra-segment partitions. You expect the same top suggestions as SuggestIndexSearcher#suggest, or a loud error if this path is unsupported, because BulkScorer#score must score only the documents in [min, max) and a timeout that never fires must not change results. Instead CompletionScorer runs its whole-segment top-N lookup again on every window or partition, so the top suggestions come back several times and lower ones are dropped (500 suggestions, n=5: [499, 499, 498, 498, 497] instead of [499, 498, 497, 496, 495]; one suggestion returned 5 times; partitions: [499 x5]), while the total says EQUAL_TO and timedOut() is false.
The test shows that a CompletionQuery run through the IndexSearcher#search(Query, Collector) that SuggestIndexSearcher inherits, with a timeout that never fires, returns the same suggestion several times, because CompletionScorer ignores the BulkScorer [min, max) window and reruns its lookup on every window.
Expected vs actual
Expected 1 hit for an index with one suggestion; actual 5 (expected:<1> but was:<5>), 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:$LUCENE/lucene/suggest/build/libs/lucene-suggest-$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.search.suggest.document.TestCompletionQueryUnderTimeoutGradle 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).
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.