MemoryIndex ignores TermFrequencyAttribute, so FeatureField values and custom term frequencies are indexed as frequency 1 and their postings frequencies, term statistics, norms and scores differ from IndexWriter's (Lucene Monitor's single-document matching included)
Finding LFV-333Area: memory / MemoryIndex term inversion (custom term frequencies: FeatureField, TermFrequencyAttribute streams, DOCS_AND_CUSTOM_FREQS); reached in-tree through monitor single-document batchesPriority: mediumImpact: 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 add a document with FeatureField("features", "pagerank", 10f), or a tokenized DOCS_AND_FREQS field whose TokenStream sets TermFrequencyAttribute (for example DelimitedTermFrequencyTokenFilter on 'a|7'), to a MemoryIndex and expect its postings, statistics and scores to equal those of the same document in a one-document IndexWriter index, as they do for ordinary fields. Instead MemoryIndex.storeTerms never reads the attribute and counts every token as frequency 1: FeatureField.newLinearQuery scores 4.5918E-41 instead of 10.0, newSaturationQuery with the pivot 10 scores exactly 0.0 (MemoryIndex.search's 'no match' value) for a document that matches, and a term with custom frequency 7 reports freq 1, sumTotalTermFreq 1 and a lower BM25 score. Lucene Monitor inherits it (since 8.6.0): the same FeatureField document scores 10.0 in a two-document batch (IndexWriter path) and 4.5918E-41 when matched alone (MemoryIndex path).
The test shows that MemoryIndex ignores TermFrequencyAttribute, so a FeatureField("f", "pr", 10f) is indexed with frequency 1 and FeatureField.newLinearQuery("f", "pr", 1f) scores it wrongly.
Expected vs actual
Expected: mi.search(...) returns the feature value 10.0 (as a one-document IndexWriter index does). Actual: 4.5918E-41.
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/memory/build/libs/lucene-memory-$V.jar
CP=$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.index.memory.TestMemoryIndexFeatureFieldGradle 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.