A new IndexWriter cannot open while a non-index file in the index directory is pending deletion, because IndexFileDeleter parses that file's name as a segment name (AssertionError 'wtf? file=...' with -ea; NumberFormatException with -da for names such as app-notes.txt)
Finding LFV-625Area: index / IndexFileDeleter start-up (inflateGens) with FSDirectory pending deletionsPriority: lowImpact: crashNovelty: known outside Lucene
AI-assisted finding, confirmed by automated checks, not yet triaged by a human Lucene committer. This site files nothing upstream.
What it shows
You keep a file of your own in the index directory (or let PersistentSnapshotDeletionPolicy store its snapshots_N files there, which its javadoc allows), delete it through Lucene's FSDirectory while another process still has it open, and then open a new IndexWriter on the same Directory object; you expect the writer to open, because Lucene leaves non-index files alone and since 7.4.0 no longer refuses to start while deletes are pending. Instead the IndexWriter constructor throws: IndexFileDeleter passes every pending deletion, unfiltered, to inflateGens, which treats any name that does not start with segments or pending_segments as a segment file, so with -ea it fails the assertion 'wtf? file=snapshots_0' (or 'wtf? file=app-notes.txt'), and with -da app-notes.txt gives NumberFormatException 'For input string: "pp-notes" under radix 36'. With -da the snapshots_0 case opens, but the writer names its next segment _napshott: the segment counter jumps to 1 + Long.parseLong("napshots", 36), which is cosmetic.
Expected vs actual
- Expected: You expect the writer to open, because Lucene leaves non-index files alone and since 7.4.0 no longer refuses to start while deletes are pending.
- Actual: The IndexWriter constructor throws: IndexFileDeleter passes every pending deletion, unfiltered, to inflateGens, which treats any name that does not start with segments or pending_segments as a segment file, so with -ea it fails the assertion 'wtf? file=snapshots_0' (or 'wtf? file=app-notes.txt'), and with -da app-notes.txt gives NumberFormatException 'For input string: "pp-notes" under radix 36'.
Files
Run it
- Tested on Lucene main e1faeba08bde (2026-11-02): still reproduces.
- Tested on Lucene main a9779ef3c193 (2026-10-26): 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" $(find src -name '*.java')
# run 1: assertions off (production-like), seed DEADBEEF
java -da -dsa -Dtests.asserts=false --add-modules jdk.incubator.vector --enable-native-access=ALL-UNNAMED -Dtests.seed=DEADBEEF \
-cp "classes:$CP" org.junit.platform.console.ConsoleLauncher \
execute --select-class org.apache.lucene.index.TestPendingNonIndexFileBlocksWriterOpenGradle 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.