GroupingSearch.setCaching / setCachingInMB limit is applied per slice since #16247 (10.6.0 regression): with an IndexSearcher that has an executor, a query matching more documents than the limit is replayed from per-slice caches holding up to slices x limit instead of being purged and re-run (results unchanged)
Finding LFV-910Area: grouping / GroupingSearch two-pass caching x search / CachingCollectorManager (new in 10.6.0) under a concurrent IndexSearcherPriority: lowImpact: minorNovelty: new
AI-assisted finding, confirmed by automated checks, not yet triaged by a human Lucene committer. This site files nothing upstream.
What it shows
You enable caching for a grouped search with GroupingSearch.setCaching(600, true) (or setCachingInMB) and search through an IndexSearcher that has an executor, and expect what the unchanged javadoc says and what 10.5.2 and a sequential searcher do: the cache holds at most the limit, and when the query matches more it is purged and the second pass re-runs the query. Instead, since #16247 GroupingSearch hands the limit to the new CachingCollectorManager, which applies it to each slice separately, so with 1000 matching documents over 2 slices each slice cache stays under 600, the caches hold all 1000 documents, and the second pass is replayed (the query runs once instead of twice). Results are the same; what breaks is the documented memory bound and the replay decision, and the cache can reach (number of slices) x limit.
The test shows that with an executor searcher (6 one-doc segments, default slicing = 2 slices of 5 + 1 docs), GroupingSearch.setCaching(5, true) replays the first-pass cache although 6 docs were cached, because the limit is applied per slice (#16247).
Expected vs actual
Expected: the cache is purged and the query re-run (2 query runs, as the setCaching javadoc says and 10.5.2 does); actual: expected:<2> but was:<1> (-ea and -da).
Files
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/grouping/build/libs/lucene-grouping-$V.jar
CP=$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.grouping.TestGroupingSearchCacheLimitGradle 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).
Formal models and scripts this finding's part of the hunt used: groupingsearch-cache-limit-applied-per-slice-10-6
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.