SERVER-48648 Return updated ShardVersion in _configsvrCommitChunkMerge to avoid blind metadata refresh (BACKPORT-9095)

4 files changed, 34 insertions, 19 deletions

diff --git a/src/mongo/db/s/config/configsvr_merge_chunk_command.cpp b/src/mongo/db/s/config/configsvr_merge_chunk_command.cpp
index 117f20d6cb0..1078b740200 100644
--- a/src/mongo/db/s/config/configsvr_merge_chunk_command.cpp
+++ b/src/mongo/db/s/config/configsvr_merge_chunk_command.cpp
@@ -116,15 +116,15 @@ public:
 
         auto parsedRequest = uassertStatusOK(MergeChunkRequest::parseFromConfigCommand(cmdObj));
 
-        Status mergeChunkResult =
+        const BSONObj shardVers = uassertStatusOK(
             ShardingCatalogManager::get(opCtx)->commitChunkMerge(opCtx,
                                                                  parsedRequest.getNamespace(),
                                                                  parsedRequest.getEpoch(),
                                                                  parsedRequest.getChunkBoundaries(),
                                                                  parsedRequest.getShardName(),
-                                                                 parsedRequest.getValidAfter());
+                                                                 parsedRequest.getValidAfter()));
+        result.appendElements(shardVers);
 
-        uassertStatusOK(mergeChunkResult);
         return true;
     }
 } configsvrMergeChunkCmd;
diff --git a/src/mongo/db/s/config/sharding_catalog_manager.h b/src/mongo/db/s/config/sharding_catalog_manager.h
index 485e2923f86..de97df11fe4 100644
--- a/src/mongo/db/s/config/sharding_catalog_manager.h
+++ b/src/mongo/db/s/config/sharding_catalog_manager.h
@@ -196,13 +196,16 @@ public:
      * merged into a single larger chunk.
      * If 'validAfter' is not set, this means the commit request came from an older server version,
      * which is not history-aware.
+     *
+     * Returns a BSON object with the newly produced chunk version after the merge:
+     *   - shardVersion - The new shard version of the source shard
      */
-    Status commitChunkMerge(OperationContext* opCtx,
-                            const NamespaceString& nss,
-                            const OID& requestEpoch,
-                            const std::vector<BSONObj>& chunkBoundaries,
-                            const std::string& shardName,
-                            const boost::optional<Timestamp>& validAfter);
+    StatusWith<BSONObj> commitChunkMerge(OperationContext* opCtx,
+                                         const NamespaceString& nss,
+                                         const OID& requestEpoch,
+                                         const std::vector<BSONObj>& chunkBoundaries,
+                                         const std::string& shardName,
+                                         const boost::optional<Timestamp>& validAfter);
 
     /**
      * Updates metadata in config.chunks collection to show the given chunk in its new shard.
diff --git a/src/mongo/db/s/config/sharding_catalog_manager_chunk_operations.cpp b/src/mongo/db/s/config/sharding_catalog_manager_chunk_operations.cpp
index 0eabb6af267..699930b09b9 100644
--- a/src/mongo/db/s/config/sharding_catalog_manager_chunk_operations.cpp
+++ b/src/mongo/db/s/config/sharding_catalog_manager_chunk_operations.cpp
@@ -552,12 +552,13 @@ StatusWith<BSONObj> ShardingCatalogManager::commitChunkSplit(
     return result.obj();
 }
 
-Status ShardingCatalogManager::commitChunkMerge(OperationContext* opCtx,
-                                                const NamespaceString& nss,
-                                                const OID& requestEpoch,
-                                                const std::vector<BSONObj>& chunkBoundaries,
-                                                const std::string& shardName,
-                                                const boost::optional<Timestamp>& validAfter) {
+StatusWith<BSONObj> ShardingCatalogManager::commitChunkMerge(
+    OperationContext* opCtx,
+    const NamespaceString& nss,
+    const OID& requestEpoch,
+    const std::vector<BSONObj>& chunkBoundaries,
+    const std::string& shardName,
+    const boost::optional<Timestamp>& validAfter) {
     // This method must never be called with empty chunks to merge
     invariant(!chunkBoundaries.empty());
 
@@ -697,7 +698,10 @@ Status ShardingCatalogManager::commitChunkMerge(OperationContext* opCtx,
         ->logChange(opCtx, "merge", nss.ns(), logDetail.obj(), WriteConcernOptions())
         .ignore();
 
-    return applyOpsStatus;
+    BSONObjBuilder result;
+    mergeVersion.appendToCommand(&result);
+
+    return result.obj();
 }
 
 StatusWith<BSONObj> ShardingCatalogManager::commitChunkMigration(
diff --git a/src/mongo/db/s/merge_chunks_command.cpp b/src/mongo/db/s/merge_chunks_command.cpp
index 37cedd096eb..68bd7ab7b39 100644
--- a/src/mongo/db/s/merge_chunks_command.cpp
+++ b/src/mongo/db/s/merge_chunks_command.cpp
@@ -243,9 +243,17 @@ void mergeChunks(OperationContext* opCtx,
             configCmdObj,
             Shard::RetryPolicy::kIdempotent));
 
-    // Refresh metadata to pick up new chunk definitions (regardless of the results returned from
-    // running _configsvrCommitChunkMerge).
-    forceShardFilteringMetadataRefresh(opCtx, nss, true /* forceRefreshFromThisThread */);
+    // old versions might not have the shardVersion field
+    if (cmdResponse.response[ChunkVersion::kShardVersionField]) {
+        const auto cv = uassertStatusOK(
+            ChunkVersion::parseWithField(cmdResponse.response, ChunkVersion::kShardVersionField));
+        uassertStatusOK(onShardVersionMismatchNoExcept(
+            opCtx, nss, std::move(cv), true /* forceRefreshFromThisThread */));
+    } else {
+        // Refresh metadata to pick up new chunk definitions (regardless of the results returned
+        // from running _configsvrCommitChunkMerge).
+        forceShardFilteringMetadataRefresh(opCtx, nss, true /* forceRefreshFromThisThread */);
+    }
 
     // If _configsvrCommitChunkMerge returned an error, look at this shard's metadata to determine
     // if the merge actually did happen. This can happen if there's a network error getting the