tryDeleteDocument / tryUpdateDocValue running while commit() flushes returns a sequence number above the commit's, yet its change is in that commit

Finding LFV-471Area: index / IndexWriter sequence numbers (tryDeleteDocument, tryUpdateDocValue vs commit)Priority: lowImpact: silent wrong resultsNovelty: new

Finding page for LFV-471

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

What it shows

You call tryDeleteDocument or tryUpdateDocValue with an NRT reader while another thread is inside commit(), after the commit has fixed its sequence number and before it snapshots its segments. You expect what the commit javadoc promises ('All sequence numbers <= this value will be reflected in the commit, and all others will not'): a change whose returned number is above the commit's is not in that commit. Instead the call returns the commit's number plus one (8 against 7), yet the delete or doc-values update is already in the commit point, while deleteDocuments(Term), deleteDocuments(Query) and updateNumericDocValue(Term) in the same window get 8 too and correctly stay out.

The test shows that while commit() flushes a buffered segment (after it has fixed its sequence number), another thread calls tryDeleteDocument(nrtReader, 0); the delete gets a number above the commit's, yet it is in that commit (tryUpdateDocValue shares the code path).

Expected vs actual

Expected, per the commit() javadoc ("All sequence numbers <= this value will be reflected in the commit, and all others will not"): seqNo 7 > commit 6, so not in the commit. Actual: tryDeleteDocument seqNo=7, commit seqNo=6, in commit expected:<false> but was:<true>.

Files

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

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: dw-flush-control-deletequeue-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 2026-11-03. AI-assisted; not yet triaged by a human Lucene committer. Feedback: open an issue in lucene-ai-bug-hunt.