TermInSetQuery.equals/hashCode ignore the rewrite method, so set queries that match different documents compare equal, and IndexWriter's delete-by-query buffer then applies only one of them

Finding LFV-321Area: core / search: TermInSetQuery equality (MultiTermQuery rewrite methods); consequence in index / IndexWriter delete-by-query bufferingPriority: lowImpact: data corruptionNovelty: new

Finding page for LFV-321

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

What it shows

Since 9.6.0 TermInSetQuery is a MultiTermQuery whose rewrite method decides which documents it matches and how it scores, but its equals/hashCode still compare only the field and terms: new TermInSetQuery("f", [a]) equals SortedSetDocValuesField.newSlowSetQuery("f", [a]) although on a field with only doc values they match 0 and 1 documents, and on an ordinary field new TermInSetQuery("f", [a, b]) equals its TopTermsScoringBooleanQueryRewrite(1) variant although they match 2 and 1 documents. You expect queries that match different documents to be unequal, as PrefixQuery, AutomatonQuery, FuzzyQuery and TermRangeQuery are when only the rewrite method differs. Instead anything keyed on the un-rewritten query treats the two as one: IndexWriter.deleteDocuments with both queries in one flush window applies only the first, so a doc-values delete silently does not happen, or a document added in between is deleted although no call matched it.

The test shows that IndexWriter.deleteDocuments(new TermInSetQuery("f", [a]), SortedSetDocValuesField.newSlowSetQuery("f", [a])) on a document whose field f has only doc values does not delete it, because TermInSetQuery.equals/hashCode ignore the rewrite method and the delete buffer keeps only the first of the two equal-comparing queries.

Expected vs actual

Expected: the doc-values query matches the document, so 0 live docs. Actual on main with -ea and with -da: 1 live doc.

Files

• src/org/apache/lucene/search/TestTermInSetQueryDeleteByDocValuesSetQuery.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=$CP:randomizedtesting-runner-2.9.2.jar:junit-4.13.2.jar:hamcrest-3.0.jar   # test-framework dependencies (Maven Central)
CP=$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.TestTermInSetQueryDeleteByDocValuesSetQuery

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.