SERVER-39234 Ensure `shardCollection` initial split works the same between config server and shard primary

1 files changed, 20 insertions, 13 deletions

diff --git a/src/mongo/db/s/shardsvr_shard_collection.cpp b/src/mongo/db/s/shardsvr_shard_collection.cpp
index 45c942eb7bb..c10ed60aed3 100644
--- a/src/mongo/db/s/shardsvr_shard_collection.cpp
+++ b/src/mongo/db/s/shardsvr_shard_collection.cpp
@@ -423,15 +423,13 @@ void shardCollection(OperationContext* opCtx,
                      bool unique,
                      const std::vector<BSONObj>& splitPoints,
                      const std::vector<TagsType>& tags,
-                     const bool fromMapReduce,
+                     bool fromMapReduce,
                      const ShardId& dbPrimaryShardId,
-                     const int numContiguousChunksPerShard,
-                     const bool isEmpty) {
+                     int numContiguousChunksPerShard,
+                     bool isEmpty) {
     const auto shardRegistry = Grid::get(opCtx)->shardRegistry();
 
     const auto primaryShard = uassertStatusOK(shardRegistry->getShard(opCtx, dbPrimaryShardId));
-    const bool distributeChunks =
-        fromMapReduce || fieldsAndOrder.isHashedPattern() || !tags.empty();
 
     // Fail if there are partially written chunks from a previous failed shardCollection.
     checkForExistingChunks(opCtx, nss);
@@ -441,9 +439,10 @@ void shardCollection(OperationContext* opCtx,
         BSONObjBuilder collectionDetail;
         collectionDetail.append("shardKey", fieldsAndOrder.toBSON());
         collectionDetail.append("collection", nss.ns());
-        if (uuid) {
+        if (uuid)
             uuid->appendToBuilder(&collectionDetail, "uuid");
-        }
+        collectionDetail.append("empty", isEmpty);
+        collectionDetail.append("fromMapReduce", fromMapReduce);
         collectionDetail.append("primary", primaryShard->toString());
         collectionDetail.append("numChunks", static_cast<int>(splitPoints.size() + 1));
         uassertStatusOK(ShardingLogging::get(opCtx)->logChangeChecked(
@@ -467,7 +466,6 @@ void shardCollection(OperationContext* opCtx,
                                                                      dbPrimaryShardId,
                                                                      splitPoints,
                                                                      tags,
-                                                                     distributeChunks,
                                                                      isEmpty,
                                                                      numContiguousChunksPerShard);
 
@@ -681,7 +679,7 @@ public:
                 std::vector<BSONObj> finalSplitPoints;
 
                 if (request.getInitialSplitPoints()) {
-                    finalSplitPoints = std::move(*request.getInitialSplitPoints());
+                    finalSplitPoints = *request.getInitialSplitPoints();
                 } else if (tags.empty()) {
                     InitialSplitPolicy::calculateHashedSplitPointsForEmptyCollection(
                         shardKeyPattern,
@@ -702,12 +700,21 @@ public:
                 LOG(0) << "CMD: shardcollection: " << cmdObj;
 
                 audit::logShardCollection(
-                    Client::getCurrent(), nss.ns(), proposedKey, request.getUnique());
+                    opCtx->getClient(), nss.ns(), proposedKey, request.getUnique());
 
-                // The initial chunks are distributed evenly across shards if the initial split
-                // points were specified in the request by mapReduce or if we are using a hashed
-                // shard key. Otherwise, all the initial chunks are placed on the primary shard.
+                // Map/reduce with output to an empty collection assumes it has full control of the
+                // output collection and it would be an unsupported operation if the collection is
+                // being concurrently written
                 const bool fromMapReduce = bool(request.getInitialSplitPoints());
+                if (fromMapReduce) {
+                    uassert(ErrorCodes::ConflictingOperationInProgress,
+                            str::stream()
+                                << "Map reduce with sharded output to a new collection found "
+                                << nss.ns()
+                                << " to be non-empty which is not supported.",
+                            isEmpty);
+                }
+
                 const int numContiguousChunksPerShard = initialSplitPoints.empty()
                     ? 1
                     : (finalSplitPoints.size() + 1) / (initialSplitPoints.size() + 1);