[BUG] Collapsing search results with concurrent segment search enabled triggers assertion error #19051
Description
Describe the bug
When collapsing search results with concurrent segment search enabled, an assertion error shardIndex is already set is triggered here:
, seems that we set the shardIndex twice.
Related component
Search
To Reproduce
- Run OpenSearch in debugging mode
- Enable concurrent segment search and execute search with field collapsing and
PUT abcd_test/_settings
{
"index.search.concurrent_segment_search.mode": "all"
}
GET abcd_test/_search?size=1
{
"query": {
"match": {
"b": "1"
}
},
"collapse": {
"field": "a"
}
}
Then you can see that an assertion error crashes the node
[2025-08-13T16:23:50,319][ERROR][o.o.b.OpenSearchUncaughtExceptionHandler] [node-1] fatal error in thread [opensearch[node-1][search][T#2]], exiting
java.lang.AssertionError: shardIndex is already set
at org.opensearch.action.search.SearchPhaseController.setShardIndex(SearchPhaseController.java:248) ~[classes/:?]
at org.opensearch.action.search.QueryPhaseResultConsumer$PendingMerges.consumeTopDocs(QueryPhaseResultConsumer.java:489) ~[classes/:?]
at org.opensearch.action.search.QueryPhaseResultConsumer.reduce(QueryPhaseResultConsumer.java:150) ~[classes/:?]
at org.opensearch.action.search.FetchSearchPhase.innerRun(FetchSearchPhase.java:136) ~[classes/:?]
at org.opensearch.action.search.FetchSearchPhase$1.doRun(FetchSearchPhase.java:122) ~[classes/:?]
at org.opensearch.common.util.concurrent.AbstractRunnable.run(AbstractRunnable.java:52) ~[classes/:?]
at org.opensearch.threadpool.TaskAwareRunnable.doRun(TaskAwareRunnable.java:78) ~[classes/:?]
at org.opensearch.common.util.concurrent.AbstractRunnable.run(AbstractRunnable.java:52) ~[classes/:?]
at org.opensearch.common.util.concurrent.TimedRunnable.doRun(TimedRunnable.java:59) ~[classes/:?]
at org.opensearch.common.util.concurrent.ThreadContext$ContextPreservingAbstractRunnable.doRun(ThreadContext.java:975) ~[classes/:?]
at org.opensearch.common.util.concurrent.AbstractRunnable.run(AbstractRunnable.java:52) ~[classes/:?]
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1144) ~[?:?]
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:642) ~[?:?]
at java.base/java.lang.Thread.run(Thread.java:1575) [?:?]
Expected behavior
shardIndex of the topDocs should be set only once.
Additional Details
Host/Environment (please complete the following information):
- Version [3.2 and main branch]
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