ToParentBlockJoinSortField on a STRING field with max-child selection and childMissingValue=STRING_LAST throws IndexOutOfBoundsException when a parent has children both with and without the field
Finding LFV-223Area: join / ToParentBlockJoinSortField string sort (ToParentDocValues missing-child ordinals, since #15727)Priority: lowImpact: crashNovelty: 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 sort parent documents by a string field of their children, descending, with new ToParentBlockJoinSortField("s", STRING, reverse=true, null, SortField.STRING_LAST, parents, children) (or the 8-argument form with reverseChildren=true), and expect the search to return the parents with children that lack the field sorted as missing-last, because the javadoc lists STRING_LAST as a legal child missing value that 'participates in the min/max selection among siblings'. Instead, as soon as the search collects a parent that has one child with the field and another child without it, it throws IndexOutOfBoundsException from the doc-values terms dictionary (Lucene90DocValuesProducer$TermsDict.seekExact via ToParentDocValues$SortedDVs.lookupOrd), with -ea and -da. The cause is that the block-join wrapper reports 'a missing child, sorted last, won the max' as the ordinal Integer.MAX_VALUE, and the string comparator TermOrdValComparator treats every ordinal other than -1 as a real one and looks it up.
The test shows that sorting block-join parents with ToParentBlockJoinSortField on a STRING field, reverseChildren=true (max child) and childMissingValue=STRING_LAST throws when a parent has one child with the field and one without (one block).
Expected vs actual
Expected the search to return the parent (1 hit); actual: IndexOutOfBoundsException from lookupOrd(Integer.MAX_VALUE) in TermOrdValComparator.copy (expected 1 sorted hit, got java.lang.IndexOutOfBoundsException), with -ea and -da.
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/join/build/libs/lucene-join-$V.jar
CP=$CP:$LUCENE/lucene/queries/build/libs/lucene-queries-$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.join.TestBlockJoinSortStringLastReverseGradle 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.