ParentsChildrenBlockJoinQuery throws IllegalStateException ('does not support intraSegment concurrency') when a scorer is requested twice for the same leaf, so IndexSearcher.explain of a BooleanQuery that contains it fails, even on a plain single-threaded searcher

Finding LFV-167Area: join / block join (ParentsChildrenBlockJoinQuery: ParentsChildrenBlockJoinWeight#scorerSupplier intra-segment guard)Priority: lowImpact: crashNovelty: new

Finding page for LFV-167

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

What it shows

You search with a BooleanQuery that combines a ParentsChildrenBlockJoinQuery with another clause and call IndexSearcher.explain on a hit, and you expect an explanation, because the Weight#scorer and Weight#scorerSupplier javadoc say a scorer (supplier) for the same LeafReaderContext may be requested multiple times as part of a single search call. Instead explain throws IllegalStateException 'ParentsChildrenBlockJoinQuery does not support intraSegment concurrency. Context ... was already seen.': the join query's Weight records every leaf it has built a scorer supplier for and refuses a second request, and BooleanWeight#explain makes exactly that second request (the join clause's own explain pulls a scorer, then BooleanWeight pulls its scorer for the same leaf to compute the score). The search itself returns the right hits; explain fails for every document that the BooleanQuery matches, including documents matched only by the other clause.

The test shows that IndexSearcher.explain of BooleanQuery(SHOULD ParentsChildrenBlockJoinQuery, SHOULD color:blue) on a one-block index (child doc 0, parent doc 1) throws, because the join Weight refuses a second scorer request for the same leaf, which BooleanWeight#explain makes (TestParentsChildrenBlockJoinExplain#testExplainOfBooleanQueryWithJoinClause).

Expected vs actual

Expected: a match explanation for doc 0 (Weight javadoc: a scorer for the same leaf may be requested multiple times); actual: IllegalStateException: ParentsChildrenBlockJoinQuery does not support intraSegment concurrency ... was already seen on a plain single-threaded searcher, with -ea and -da.

Files

• src/org/apache/lucene/search/join/TestParentsChildrenBlockJoinExplain.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=$CP:$LUCENE/lucene/join/build/libs/lucene-join-$V.jar
CP=$CP:$LUCENE/lucene/queries/build/libs/lucene-queries-$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.search.join.TestParentsChildrenBlockJoinExplain

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.