SERVER-35255: whole-cluster $changeStreams send listCollections to the config server for the 'admin' and/or 'config' databases

(cherry picked from commit 2a60402197dbbfe65894beaa54936bd657e7bf20)

1 files changed, 7 insertions, 0 deletions

diff --git a/src/mongo/s/commands/cluster_aggregate.cpp b/src/mongo/s/commands/cluster_aggregate.cpp
index 6bc5cc2a9ef..e745feb72bc 100644
--- a/src/mongo/s/commands/cluster_aggregate.cpp
+++ b/src/mongo/s/commands/cluster_aggregate.cpp
@@ -619,6 +619,13 @@ BSONObj establishMergingMongosCursor(OperationContext* opCtx,
 
 BSONObj getDefaultCollationForUnshardedCollection(const Shard* primaryShard,
                                                   const NamespaceString& nss) {
+    // Because collectionless aggregations are generally run against the 'admin' database, the
+    // standard logic will attempt to resolve its non-existent collation by sending a specious
+    // 'listCollections' command to the config servers. To prevent this, we immediately return an
+    // empty BSONObj if the namespace is collectionless.
+    if (nss.isCollectionlessAggregateNS()) {
+        return BSONObj();
+    }
     ScopedDbConnection conn(primaryShard->getConnString());
     BSONObj defaultCollation;
     std::list<BSONObj> all =