openIfChanged returns null and isCurrent() stays true after a flush when the only changes are doc-values updates

Finding LFV-001Area: index / IndexWriter NRTPriority: highImpact: silent wrong resultsNovelty: new

Finding page for LFV-001

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

What it shows

You open an NRT reader, update a doc-values field (or soft-delete through updateDocValues), and then call flush(), a no-op forceMerge(1), or open readers with writeAllDeletes=true. You expect DirectoryReader.openIfChanged(reader, writer) to return a reader that sees the change. Instead it returns null and reader.isCurrent() is true, so SearcherManager keeps the stale searcher, and hasUncommittedChanges() can also return false while updates are uncommitted.

The test shows that after an NRT reader is opened, IndexWriter#updateNumericDocValue followed by flush() leaves DirectoryReader.openIfChanged(reader, writer) returning null, so the reader never sees the update.

Expected vs actual

Expected a new reader (the writer has an update the reader does not see); actual: null, with -ea and -da (AssertionError: expected a new reader after a doc-values update, but got null).

Files

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

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.