TaxonomyFacetFloatAssociations with a DoubleValuesSource reports a too-high LabelAndValue.count for every label that has matching documents below it in a hierarchical dimension, because FloatTaxonomyFacets rolls the counts up again at every ancestor level (values are right; every release since 9.11.0)

Finding LFV-539Area: facet / taxonomy association facets (TaxonomyFacetFloatAssociations value-source path, FloatTaxonomyFacets#updateValueFromRollup count roll-up)Priority: mediumImpact: silent wrong resultsNovelty: new

Finding page for LFV-539

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

What it shows

You index documents with a FacetField in a dimension declared hierarchical (FacetsConfig.setHierarchical("d", true)), for example d/a/x with weight 7 and d/a/y with weight 2, and sum a per-document DoubleValuesSource per label with TaxonomyFacetFloatAssociations; you expect label a under d to report value 9 and count 2, the 'Number of occurrences for this label' that FastTaxonomyFacetCounts reports for the same hits. Instead getTopChildren and getAllChildren report a (9.0) with count 4, because FloatTaxonomyFacets#updateValueFromRollup first calls super.updateValueFromRollup, which rolls up the counts of the whole sub-tree, and then its own rollup(childOrdinal), which calls updateValueFromRollup again for every descendant, so the sub-tree counts are added once more at each ancestor level. Values and leaf counts are right; only LabelAndValue.count of labels with descendants is inflated, and the deeper the tree, the larger the overcount.

The test shows that TaxonomyFacetFloatAssociations with a DoubleValuesSource on a hierarchical dimension rolls the counts up twice: one document at d/a/x.

Expected vs actual

Expected LabelAndValue.count of d/a = 1 (one document under it). Actual: 2, because FloatTaxonomyFacets#updateValueFromRollup calls super (a full count roll-up) and then its own rollup, which rolls the sub-tree counts up again.

Files

Run it

# 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
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.TestFloatValueSourceRollupCounts

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 2026-11-03. AI-assisted; not yet triaged by a human Lucene committer. Feedback: open an issue in lucene-ai-bug-hunt.