Word2VecSynonymFilterFactory accepts any positive maxSynonymsPerTerm, but Word2VecSynonymProvider sizes its HNSW search as maxSynonymsPerTerm + 1 with no clamp to the model size, so very large values (Integer.MAX_VALUE, where the + 1 overflows) make every in-model token throw IllegalArgumentException or OutOfMemoryError

Finding LFV-866Area: analysis-common / synonym.word2vec (Word2VecSynonymProvider.getSynonyms search size; Word2VecSynonymFilterFactory validation)Priority: lowImpact: crashNovelty: new

Finding page for LFV-866

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 Word2VecSynonymFilterFactory with maxSynonymsPerTerm=2147483647 (Integer.MAX_VALUE), which its validation accepts ('must be a positive integer greater than 0'), to keep every synonym above minAcceptedSimilarity, and you expect those synonyms or a rejection at configuration time. The analyzer builds, but Word2VecSynonymProvider.getSynonyms passes maxSynonymsPerTerm + 1 (int arithmetic) as topK to HnswGraphSearcher.search, which wraps to Integer.MIN_VALUE, so the first token with a model vector throws IllegalArgumentException 'initialCapacity must be > 0 and < 2147483630; got: -2147483648' from TernaryLongHeap (on 9.7.0 to 10.3.2: 'maxSize must be > 0 ...' from LongHeap). Because the search size is never clamped to the model size and the search allocates its queues of topK entries up front, values close to Integer.MAX_VALUE fail the same way and values from roughly heap-bytes/16 up (1e8 at a 1 GiB heap) throw OutOfMemoryError, even for a 3-term model.

The test shows that Word2VecSynonymFilterFactory accepts maxSynonymsPerTerm=Integer.MAX_VALUE, but the first token that has a model vector then fails, because the HNSW search size maxSynonymsPerTerm + 1 overflows and is never clamped to the model size.

Expected vs actual

Expected "alpha" to analyse to [alpha, beta] (or a rejection at configuration time); actual: IllegalArgumentException: initialCapacity must be > 0 and < 2147483630; got: -2147483648 from TernaryLongHeap, with -ea and -da.

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=$CP:$LUCENE/lucene/analysis/common/build/libs/lucene-analysis-common-$V.jar
CP=$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.analysis.synonym.word2vec.TestWord2VecLargeMaxSynonymsPerTerm

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

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Snapshot of 2026-11-04. AI-assisted; not yet triaged by a human Lucene committer. Feedback: open an issue in lucene-ai-bug-hunt.