IndexWriter.forceApply marks a re-resolving update packet finished outside the IndexWriter lock when its re-iteration matches no segment, so a merge that commits in that gap skips the packet's already-resolved doc-values updates and nobody applies them again: an acknowledged updateNumericDocValue/updateDocValues is lost and softUpdateDocument leaves two live versions of the document, also after commit (since 7.0.0)

Finding LFV-596Area: index / IndexWriter frozen update packets vs. merge carry-over (forceApply, commitMergedDeletesAndUpdates, BufferedUpdatesStream)Priority: mediumImpact: data corruptionNovelty: known upstream

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

What it shows

You update a document's doc-values field (updateNumericDocValue, updateDocValues) or replace a document with softUpdateDocument while background merges run; IndexWriter returns a sequence number, so every later NRT reader and commit should show the change. If the update packet must re-resolve because a merge committed meanwhile and that merge's result was dropped as fully deleted, IndexWriter.forceApply finds no segment left, leaves the IndexWriter lock and only then marks the packet finished; a second merge that commits in that gap treats the packet as still running, skips its already-resolved update on the merged-away segment, and nobody applies it again. The update is silently lost (id 3 keeps value 30 instead of 7, also after commit and reopen), and with softUpdateDocument the old version is never soft-deleted, so two live versions of one document remain.

Expected vs actual

Files

Run it

# 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.TestEmptyReResolveLosesDocValuesUpdate

# run 2: assertions on, seed DEADBEEF, default flags
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.TestEmptyReResolveLosesDocValuesUpdate8x

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: frozen-updates-apply-merge-carryover-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.