An IndexWriter opened from a reader's IndexCommit whose constructor then fails (for example the IndexDeletionPolicy's onInit throws, or an I/O error while the deleter reads a commit) never releases the segment readers its ReaderPool pre-enrolled from that reader, so the reader's segment files stay open after the caller closes the reader

Finding LFV-1065Area: core / IndexWriter constructor failure path (reader-commit branch: IndexWriterConfig#setIndexCommit(reader.getIndexCommit()), ReaderPool pre-enrollment; LUCENE-6524, LUCENE-8260)Priority: lowImpact: minorNovelty: new

Finding page for LFV-1065

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 a DirectoryReader, pass its getIndexCommit() to IndexWriterConfig#setIndexCommit, and the IndexWriter constructor then fails, here because your IndexDeletionPolicy's onInit throws an IOException; you expect the exception and nothing left behind once you close the reader, as the constructor's own catch intends (it releases the write lock and, since #15675, the merge scheduler) and as the same failure with a commit from DirectoryReader.listCommits behaves. Instead the constructor has already built the ReaderPool, which pre-enrolled one SegmentReader per segment, each holding a reference on the reader's segment core, and its catch never closes the pool, so after reader.close() MockDirectoryWrapper still reports the segment's compound file open.

Expected vs actual

• Expected: After r.close(), dir.close() succeeds: the failed constructor left no segment file open.
• Actual: MockDirectoryWrapper: cannot close: there are still 1 open files: {_0.cfs=1} (an unclosed _0.cfs opened by the segment core), assertions on and off, on main and 10.6.0.

Files

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

Run it

• Tested on Lucene main e1faeba08bde (2026-11-02): still reproduces.
• Tested on Lucene main 645d4fe14a20 (2026-10-28): 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.TestIndexWriterFromReaderFailedOpen

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).

Files shown on the finding page

• TestIndexWriterFromReaderFailedOpen.java

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.