SERVER-41249 Fix special cases for $out to include $merge

3 files changed, 7 insertions, 6 deletions

diff --git a/src/mongo/s/query/cluster_aggregate.cpp b/src/mongo/s/query/cluster_aggregate.cpp
index 2cbb292adc8..64538f676cc 100644
--- a/src/mongo/s/query/cluster_aggregate.cpp
+++ b/src/mongo/s/query/cluster_aggregate.cpp
@@ -625,8 +625,9 @@ Status runPipelineOnMongoS(const boost::intrusive_ptr<ExpressionContext>& expCtx
     auto cursorResponse = establishMergingMongosCursor(
         opCtx, request, requestedNss, litePipe, std::move(pipeline), privileges);
 
-    // We don't need to storePossibleCursor or propagate writeConcern errors; an $out pipeline
-    // can never run on mongoS. Filter the command response and return immediately.
+    // We don't need to storePossibleCursor or propagate writeConcern errors; a pipeline with
+    // writing stages like $out can never run on mongoS. Filter the command response and return
+    // immediately.
     CommandHelpers::filterCommandReplyForPassthrough(cursorResponse, result);
     return getStatusFromCommandResult(result->asTempObj());
 }
diff --git a/src/mongo/s/query/cluster_aggregation_planner_test.cpp b/src/mongo/s/query/cluster_aggregation_planner_test.cpp
index 8f14dceeb6a..a6a81e7a5d4 100644
--- a/src/mongo/s/query/cluster_aggregation_planner_test.cpp
+++ b/src/mongo/s/query/cluster_aggregation_planner_test.cpp
@@ -55,7 +55,7 @@ const NamespaceString kTestOutNss = NamespaceString{"unittests", "out_ns"};
 
 /**
  * For the purposes of this test, assume every collection is sharded. Stages may ask this during
- * setup. For example, to compute its constraints, the $out stage needs to know if the output
+ * setup. For example, to compute its constraints, the $merge stage needs to know if the output
  * collection is sharded.
  */
 class FakeMongoProcessInterface : public StubMongoProcessInterface {
diff --git a/src/mongo/s/transaction_router.cpp b/src/mongo/s/transaction_router.cpp
index 667ba573f17..a5b8a864bbc 100644
--- a/src/mongo/s/transaction_router.cpp
+++ b/src/mongo/s/transaction_router.cpp
@@ -145,9 +145,9 @@ BSONObjBuilder appendFieldsForStartTransaction(BSONObj cmd,
 }
 
 // Commands that are idempotent in a transaction context and can be blindly retried in the middle of
-// a transaction. Aggregate with $out is disallowed in a transaction, so aggregates must be read
-// operations. Note: aggregate and find do have the side-effect of creating cursors, but any
-// established during an unsuccessful attempt are best-effort killed.
+// a transaction. Writing aggregates (e.g. with a $out or $merge) is disallowed in a transaction, so
+// aggregates must be read operations. Note: aggregate and find do have the side-effect of creating
+// cursors, but any established during an unsuccessful attempt are best-effort killed.
 const StringMap<int> alwaysRetryableCmds = {
     {"aggregate", 1}, {"distinct", 1}, {"find", 1}, {"getMore", 1}, {"killCursors", 1}};