SERVER-31866 setFCV should always wait for majority writeConcern

4 files changed, 22 insertions, 5 deletions

diff --git a/src/mongo/s/catalog/sharding_catalog_manager.cpp b/src/mongo/s/catalog/sharding_catalog_manager.cpp
index b9808971703..1c0b2f0ffc7 100644
--- a/src/mongo/s/catalog/sharding_catalog_manager.cpp
+++ b/src/mongo/s/catalog/sharding_catalog_manager.cpp
@@ -313,7 +313,7 @@ Status ShardingCatalogManager::_initConfigIndexes(OperationContext* opCtx) {
 }
 
 Status ShardingCatalogManager::setFeatureCompatibilityVersionOnShards(OperationContext* opCtx,
-                                                                      const std::string& version) {
+                                                                      const BSONObj& cmdObj) {
 
     // No shards should be added until we have forwarded featureCompatibilityVersion to all shards.
     Lock::SharedLock lk(opCtx->lockState(), _kShardMembershipLock);
@@ -331,7 +331,7 @@ Status ShardingCatalogManager::setFeatureCompatibilityVersionOnShards(OperationC
             opCtx,
             ReadPreferenceSetting{ReadPreference::PrimaryOnly},
             "admin",
-            BSON(FeatureCompatibilityVersion::kCommandName << version),
+            cmdObj,
             Shard::RetryPolicy::kIdempotent);
         if (!response.isOK()) {
             return response.getStatus();
diff --git a/src/mongo/s/catalog/sharding_catalog_manager.h b/src/mongo/s/catalog/sharding_catalog_manager.h
index c0c0ae2c605..cd36a69cbfe 100644
--- a/src/mongo/s/catalog/sharding_catalog_manager.h
+++ b/src/mongo/s/catalog/sharding_catalog_manager.h
@@ -304,8 +304,7 @@ public:
     /**
      * Runs the setFeatureCompatibilityVersion command on all shards.
      */
-    Status setFeatureCompatibilityVersionOnShards(OperationContext* opCtx,
-                                                  const std::string& version);
+    Status setFeatureCompatibilityVersionOnShards(OperationContext* opCtx, const BSONObj& cmdObj);
 
     //
     // For Diagnostics
diff --git a/src/mongo/s/catalog/sharding_catalog_manager_collection_operations.cpp b/src/mongo/s/catalog/sharding_catalog_manager_collection_operations.cpp
index 90f54be2fe6..812110d838a 100644
--- a/src/mongo/s/catalog/sharding_catalog_manager_collection_operations.cpp
+++ b/src/mongo/s/catalog/sharding_catalog_manager_collection_operations.cpp
@@ -45,6 +45,7 @@
 #include "mongo/db/namespace_string.h"
 #include "mongo/db/operation_context.h"
 #include "mongo/db/query/collation/collator_factory_interface.h"
+#include "mongo/db/repl/repl_client_info.h"
 #include "mongo/executor/task_executor.h"
 #include "mongo/rpc/get_status_from_command_result.h"
 #include "mongo/s/balancer_configuration.h"
@@ -338,6 +339,18 @@ void ShardingCatalogManager::generateUUIDsForExistingShardedCollections(Operatio
                             ))
             .docs;
 
+    if (shardedColls.empty()) {
+        LOG(0) << "all sharded collections already have UUIDs";
+
+        // We did a local read of the collections collection above and found that all sharded
+        // collections already have UUIDs. However, the data may not be majority committed (a
+        // previous setFCV attempt may have failed with a write concern error). Since the current
+        // Client doesn't know the opTime of the last write to the collections collection, make it
+        // wait for the last opTime in the system when we wait for writeConcern.
+        repl::ReplClientInfo::forClient(opCtx->getClient()).setLastOpToSystemLastOpTime(opCtx);
+        return;
+    }
+
     // Generate and persist a new UUID for each collection that did not have a UUID.
     LOG(0) << "generating UUIDs for " << shardedColls.size()
            << " sharded collections that do not yet have a UUID";
diff --git a/src/mongo/s/catalog/sharding_catalog_manager_shard_operations.cpp b/src/mongo/s/catalog/sharding_catalog_manager_shard_operations.cpp
index 38b8295e1c9..97a28b4a3b1 100644
--- a/src/mongo/s/catalog/sharding_catalog_manager_shard_operations.cpp
+++ b/src/mongo/s/catalog/sharding_catalog_manager_shard_operations.cpp
@@ -660,7 +660,12 @@ StatusWith<std::string> ShardingCatalogManager::addShard(
         return batchResponseStatus;
     }
 
-    // The featureCompatibilityVersion should be the same throughout the cluster.
+    // The featureCompatibilityVersion should be the same throughout the cluster. We don't
+    // explicitly send writeConcern majority to the added shard, because a 3.4 mongod will reject
+    // it (setFCV did not support writeConcern until 3.6), and a 3.6 mongod will still default to
+    // majority writeConcern.
+    //
+    // TODO SERVER-32045: propagate the user's writeConcern
     auto versionResponse = _runCommandForAddShard(
         opCtx,
         targeter.get(),