Range facet counters add every hit the fastMatchQuery rejects to FacetResult.value, so the dimension total is too high and depends on the segment layout

Finding LFV-151Area: facet / range and range-on-range facet counts (FacetResult.value with a fastMatchQuery)Priority: lowImpact: silent wrong resultsNovelty: new

Finding page for LFV-151

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

What it shows

You build a range facet counter (LongRangeFacetCounts or DoubleRangeFacetCounts on a single-valued field or values source, or a range-on-range counter) with a fastMatchQuery that removes only hits outside every range, which is what it is for, and read FacetResult.value. You expect the same dimension total as without the fastMatchQuery: the number of hits that fall into at least one range. Instead each segment adds all of its hits up front but subtracts only the documents the fastMatchQuery let through, so the hits it rejected stay in the total (3 instead of 1 in the minimal repro, while the range count is 1), and the same documents and query give 3 in one segment and 1 in two.

The test shows that LongRangeFacetCounts with a fastMatchQuery that only rejects documents outside the range counts those rejected hits in FacetResult.value (one segment, v = 0, 10, 20, range [0,5]).

Expected vs actual

Expected total 1 (only v=0 is in a range, the same as without the fastMatchQuery); actual 3 (expected:<1> but was:<3>).

Files

• src/org/apache/lucene/facet/range/TestLongRangeFacetFastMatchTotal.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/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.range.TestLongRangeFacetFastMatchTotal

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).

Formal models and scripts this finding's part of the hunt used: facet-taxonomy-ranges

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.