With an index sort, a failure while creating the sorted stored-fields or term-vectors writer during flush leaves the reader on the temporary .fdt/.fdx (.tvd/.tvx) files open after IndexWriter closes itself

Finding LFV-440Area: index / flush-time index sorting (SortingStoredFieldsConsumer, SortingTermVectorsConsumer)Priority: lowImpact: minorNovelty: new

Finding page for LFV-440

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

What it shows

You configure an index sort, and while a flush is creating the final sorted stored-fields (or term-vectors) files, creating or opening a file fails with an IOException, for example because the process has too many open files. You expect IndexWriter to close itself, as it does after any failed flush, and to release every file it opened. Instead the reader that the flush had just opened on the temporary .fdt/.fdx (or .tvd/.tvx) files is never closed, because it is opened one statement before the try whose finally closes it, so two inputs on already-deleted temporary files stay open (on MMapDirectory, mapped) after IndexWriter and the Directory are closed.

The test shows that with an index sort, when creating the final sorted stored-fields writer fails during flush (createOutput of .fdm throws), IndexWriter closes itself but the reader on the temporary .fdt/.fdx files stays open.

Expected vs actual

Expected: no open file handles after the failed commit() and close(). Actual: open file handles after IndexWriter closed expected:<0> but was:<2>.

Files

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

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.