SERVER-30899 Aggregations sent from a 3.4 mongos should serialize 3.4 metadata

1 files changed, 24 insertions, 6 deletions

diff --git a/src/mongo/db/pipeline/aggregation_request.h b/src/mongo/db/pipeline/aggregation_request.h
index d8672b986d7..b34fc383d20 100644
--- a/src/mongo/db/pipeline/aggregation_request.h
+++ b/src/mongo/db/pipeline/aggregation_request.h
@@ -50,8 +50,9 @@ public:
     static constexpr StringData kCommandName = "aggregate"_sd;
     static constexpr StringData kCursorName = "cursor"_sd;
     static constexpr StringData kBatchSizeName = "batchSize"_sd;
-    static constexpr StringData kFromRouterName = "fromRouter"_sd;
+    static constexpr StringData kFromMongosName = "fromMongos"_sd;
     static constexpr StringData kNeedsMergeName = "needsMerge"_sd;
+    static constexpr StringData kNeedsMerge34Name = "fromRouter"_sd;
     static constexpr StringData kPipelineName = "pipeline"_sd;
     static constexpr StringData kCollationName = "collation"_sd;
     static constexpr StringData kExplainName = "explain"_sd;
@@ -135,8 +136,15 @@ public:
     /**
      * Returns true if this request originated from a mongoS.
      */
-    bool isFromRouter() const {
-        return _fromRouter;
+    bool isFromMongos() const {
+        return _fromMongos;
+    }
+
+    /**
+     * Returns true if this request originated from a 3.4 mongos.
+     */
+    bool isFrom34Mongos() const {
+        return _from34Mongos;
     }
 
     /**
@@ -218,8 +226,12 @@ public:
         _allowDiskUse = allowDiskUse;
     }
 
-    void setFromRouter(bool isFromRouter) {
-        _fromRouter = isFromRouter;
+    void setFromMongos(bool isFromMongos) {
+        _fromMongos = isFromMongos;
+    }
+
+    void setFrom34Mongos(bool isFrom34Mongos) {
+        _from34Mongos = isFrom34Mongos;
     }
 
     void setNeedsMerge(bool needsMerge) {
@@ -276,10 +288,16 @@ private:
     boost::optional<ExplainOptions::Verbosity> _explainMode;
 
     bool _allowDiskUse = false;
-    bool _fromRouter = false;
+    bool _fromMongos = false;
     bool _needsMerge = false;
     bool _bypassDocumentValidation = false;
 
+    // We track whether the aggregation request came from a 3.4 mongos. If so, the merge may occur
+    // on a 3.4 shard (which does not understand sort key metadata), and we should not serialize the
+    // sort key.
+    // TODO SERVER-30924: remove this.
+    bool _from34Mongos = false;
+
     // A user-specified maxTimeMS limit, or a value of '0' if not specified.
     unsigned int _maxTimeMS = 0;
 };