With assertions enabled, re-sorting an index with document blocks through SortingCodecReader and addIndexes fails SortingCodecReader's cache assertion for the parent field

Finding LFV-112Area: index / SortingCodecReader re-sort (index sorting with document blocks)Priority: lowImpact: minorNovelty: new

Finding page for LFV-112

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

What it shows

You re-sort an index that uses document blocks and a parent field (IndexWriterConfig#setParentField) the way the SortingCodecReader javadoc describes: wrap each segment with SortingCodecReader.wrap(reader, newSort) and pass the wrapped readers to IndexWriter#addIndexes(CodecReader...) of a fresh writer with the new index sort and the same parent field. You expect the re-sort to succeed, as it does with assertions disabled (the result is then correctly sorted with every block intact) and as it does for an index without blocks. Instead, with Java assertions enabled (-ea), addIndexes throws AssertionError 'only sort fields should be cached twice but [_parent] is not a sort field' and the destination writer closes, because MultiSorter reads the parent field's doc values once to find the blocks and the doc-values merge reads them again, while SortingCodecReader's internal check allows a second read only for sort fields.

The test shows that re-sorting an index with document blocks and a parent field through SortingCodecReader.wrap + IndexWriter#addIndexes(CodecReader...) (the recipe in the SortingCodecReader javadoc) trips SortingCodecReader's doc-values cache assertion, because MultiSorter and the doc-values merge both read the _parent field.

Expected vs actual

Expected addIndexes to succeed; actual with -ea: AssertionError: only sort fields should be cached twice but [_parent] is not a sort field. With -da the test passes, as the claim says (assertion-only bug).

Files

• src/org/apache/lucene/index/TestSortingCodecReaderParentField.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.index.TestSortingCodecReaderParentField

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 2026-11-04. AI-assisted; not yet triaged by a human Lucene committer. Feedback: open an issue in lucene-ai-bug-hunt.