Fix inner hits + aggregations concurrency bug #128036
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benchaplin
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javanna
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May 19, 2025
...er/src/internalClusterTest/java/org/elasticsearch/search/aggregations/metrics/TopHitsIT.java
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Resolves #122419.
There's a concurrency bug that occurs when doing aggregations on inner hits. It can result in one of three exceptions:
java.lang.IllegalStateException: Error retrieving pathjava.lang.NullPointerException: Cannot invoke "java.util.Map.get(Object)" because "this.preloadedStoredFieldValues" is nulljava.lang.AssertionError: invalid decRef call: already closedThe underlying issue is that
InnerHitSubContextis not thread safe, yet instances are shared across leaf slice search threads during an aggregation. Specifically, the race condition occurs whenInnerHitSubContext.rootId&InnerHitSubContext.rootSourcefields are set and accessed concurrently by multiple threads.The tests I've added to
TopHitsITreproduce the issue. If you paste those tests into main and run them a few times you should see one of the exceptions.I've solved this by forking the
InnerHitSubContextinstances, similar to what was done here #106990.SearchExecutionContextis at times accessed fromInnerHitSubContext, so I also had to make sure the forkedSearchExecutionContextwas used in those cases.