Facets#getTopDims on taxonomy association and value-source facets leaves out a dimension that has hits but whose aggregated value is exactly 0, although getAllDims returns it (known: #13191 / open PR #13287) (released since 9.11.0)

Finding LFV-1104Area: facet / taxonomy facets getTopDims (TaxonomyFacets dimension admission)Priority: lowImpact: silent wrong resultsNovelty: known upstream

AI-assisted finding, reproduced on Lucene main but not yet independently re-verified, and not yet triaged by a human Lucene committer. This site files nothing upstream.

What it shows

You index one document with IntAssociationFacetField(0, "a", "x") and one with IntAssociationFacetField(1, "b", "x"), aggregate them with TaxonomyFacetIntAssociations and SUM, and call getTopDims(10, 10), expecting [b=1, a=0], the same as getAllDims(10), as the Facets#getTopDims javadoc says. Instead getTopDims returns [b=1]: it admits a dimension only when its value is not 0 (TaxonomyFacets.java:652), while getAllDims has reported zero-valued dimensions with hits since 9.11.0. Float associations behave the same.

Expected vs actual

• Expected: The test passes: it asserts the documented behaviour.
• Actual: getTopDims returns [b=1]: it admits a dimension only when its value is not 0 (TaxonomyFacets.java:652), while getAllDims has reported zero-valued dimensions with hits since 9.11.0.

Files

• src/org/apache/lucene/facet/taxonomy/TestGetTopDimsZeroValuedDim.java (JUnit test)

Run it

• Tested on Lucene main e1faeba08bde (2026-11-02): reproduced.
• Tested on Lucene main ea57360912ed (2026-10-24): reproduced.
• 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/facet/build/libs/lucene-facet-$V.jar
CP=$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, default flags
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.facet.taxonomy.TestGetTopDimsZeroValuedDim

The module(s) facet also need their third-party runtime jars; ./gradlew -p lucene/<module> dependencies lists them.

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).

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.