SegmentInfos.FindSegmentsFile's double listAll() check misses a weakly consistent listing when each of its two listings overlaps one complete commit, so opening a healthy index can throw IndexNotFoundException (residual of open #3659 / LUCENE-2585; shown only with a simulated weakly consistent listing)

Finding LFV-1092Area: index / SegmentInfos.FindSegmentsFile (commit discovery)Priority: lowImpact: crashNovelty: known upstream

AI-assisted finding, reproduced on Lucene main but not yet independently re-verified, and not yet triaged by a human Lucene committer. This site files nothing upstream.

What it shows

You open a healthy index while a writer commits and expect DirectoryReader.open to open one of the commits that existed during the call; FindSegmentsFile lists the directory twice to detect a concurrent change, as its comment says listAll() is weakly consistent. If each of the two listings overlaps one complete commit (rename to segments_N+1, then deletion of segments_N) and omits both segments files, the two listings are equal and open throws IndexNotFoundException 'no segments* file found'; this is shown with a simulated listing that returns only the files present for the whole call.

Expected vs actual

• Expected: The test passes: it asserts the documented behaviour.
• Actual: While the reported behaviour is present the test fails; the failure message states expected against actual.

Files

• src/org/apache/lucene/index/TestFindSegmentsFileWeakListing.java (JUnit test)

Run it

• Tested on Lucene main e1faeba08bde (2026-11-02): reproduced.
• Tested on Lucene main ea57360912ed (2026-10-24): reproduced.
• 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.TestFindSegmentsFileWeakListing

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).

Formal models and scripts this finding's part of the hunt used: findsegmentsfile-commit-discovery-tla

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.