DirectoryReader.openIfChanged on a reader opened with a leaf sorter leaks segment reader references when the sorter throws while the new reader is built, so closing the old reader no longer closes the shared segments and the new segment's reader is never closed

Finding LFV-1059Area: core / index reader reopen (StandardDirectoryReader reopen factory behind every non-NRT openIfChanged, with a leaf sorter, LUCENE-9507)Priority: lowImpact: minorNovelty: new

Finding page for LFV-1059

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 with a leaf sorter and later call DirectoryReader.openIfChanged; if the sorter throws while the new reader sorts its leaves, you expect only that exception, because the javadoc makes you responsible just for the old reader and the initial open releases its readers in exactly this case. Instead the reopen factory has already taken a reference on each reused segment reader and opened the new ones, and it builds the new reader with no try/catch, so after the failed call the shared segment reader's refCount is 2 instead of 1 (1 instead of 0 after you close the old reader) and the new segment's reader is never closed.

Expected vs actual

Expected: After the failed openIfChanged, the shared segment reader is back at refCount 1, owned only by reader.
Actual: AssertionError: expected:<1> but was:<2>: the failed call kept its reference; assertions on and off on main, and on 10.6.0.

Files

src/org/apache/lucene/index/TestReopenSorterFailureRefCount.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 off (production-like), seed DEADBEEF
java -da -dsa -Dtests.asserts=false -Xmx2g --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.TestReopenSorterFailureRefCount

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

TestReopenSorterFailureRefCount.java

Formal models and scripts this finding's part of the hunt used: never-judged-backlog-closure-low-and-not-a-bug

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.