SERVER-25204 Allow writeConcern w:1 for 'local' on CSRS config servers

5 files changed, 22 insertions, 10 deletions

diff --git a/src/mongo/db/commands/get_last_error.cpp b/src/mongo/db/commands/get_last_error.cpp
index 498d32d9d0c..899d081926d 100644
--- a/src/mongo/db/commands/get_last_error.cpp
+++ b/src/mongo/db/commands/get_last_error.cpp
@@ -221,8 +221,10 @@ public:
         // Validate write concern no matter what, this matches 2.4 behavior
         //
         if (status.isOK()) {
-            // Ensure options are valid for this host
-            status = validateWriteConcern(txn, writeConcern);
+            // Ensure options are valid for this host. Since getLastError doesn't do writes itself,
+            // treat it as if these are admin database writes, which need to be replicated so we do
+            // the strictest checks write concern checks.
+            status = validateWriteConcern(txn, writeConcern, NamespaceString::kAdminDb);
         }
 
         if (!status.isOK()) {
diff --git a/src/mongo/db/namespace_string.cpp b/src/mongo/db/namespace_string.cpp
index db22280231b..5b53b509c5f 100644
--- a/src/mongo/db/namespace_string.cpp
+++ b/src/mongo/db/namespace_string.cpp
@@ -96,6 +96,9 @@ bool legalClientSystemNS(StringData ns, bool write) {
     return false;
 }
 
+const StringData NamespaceString::kAdminDb = "admin"_sd;
+const StringData NamespaceString::kLocalDb = "local"_sd;
+
 const NamespaceString NamespaceString::kConfigCollectionNamespace(kConfigCollection);
 
 bool NamespaceString::isListCollectionsCursorNS() const {
diff --git a/src/mongo/db/namespace_string.h b/src/mongo/db/namespace_string.h
index 3b21be69a90..7ffb802cb1e 100644
--- a/src/mongo/db/namespace_string.h
+++ b/src/mongo/db/namespace_string.h
@@ -57,6 +57,12 @@ class NamespaceString {
 public:
     // Reserved system namespaces
 
+    // Namespace for the admin database
+    static const StringData kAdminDb;
+
+    // Namespace for the local database
+    static const StringData kLocalDb;
+
     // Namespace for storing configuration data, which needs to be replicated if the server is
     // running as a replica set. Documents in this collection should represent some configuration
     // state of the server, which needs to be recovered/consulted at startup. Each document in this
diff --git a/src/mongo/db/write_concern.cpp b/src/mongo/db/write_concern.cpp
index a9c9adf1b99..6e986d87b19 100644
--- a/src/mongo/db/write_concern.cpp
+++ b/src/mongo/db/write_concern.cpp
@@ -83,7 +83,7 @@ StatusWith<WriteConcernOptions> extractWriteConcern(OperationContext* txn,
         }
     } else if (supportsWriteConcern) {
         // If it supports writeConcern and does not use the default, validate the writeConcern.
-        Status wcStatus = validateWriteConcern(txn, writeConcern);
+        Status wcStatus = validateWriteConcern(txn, writeConcern, dbName);
         if (!wcStatus.isOK()) {
             return wcStatus;
         }
@@ -96,7 +96,9 @@ StatusWith<WriteConcernOptions> extractWriteConcern(OperationContext* txn,
     return writeConcern;
 }
 
-Status validateWriteConcern(OperationContext* txn, const WriteConcernOptions& writeConcern) {
+Status validateWriteConcern(OperationContext* txn,
+                            const WriteConcernOptions& writeConcern,
+                            StringData dbName) {
     if (writeConcern.syncMode == WriteConcernOptions::SyncMode::JOURNAL &&
         !txn->getServiceContext()->getGlobalStorageEngine()->isDurable()) {
         return Status(ErrorCodes::BadValue,
@@ -107,7 +109,7 @@ Status validateWriteConcern(OperationContext* txn, const WriteConcernOptions& wr
     // logic) should never be making non-majority writes against the config server, because sharding
     // is not resilient against rollbacks of metadata writes.
     if (serverGlobalParams.clusterRole == ClusterRole::ConfigServer &&
-        !writeConcern.validForConfigServers()) {
+        dbName != NamespaceString::kLocalDb && !writeConcern.validForConfigServers()) {
         // The only cases where we allow non-majority writes are from within the config servers
         // themselves, because these wait for write concern explicitly.
         if (!txn->getClient()->isInDirectClient()) {
@@ -176,9 +178,6 @@ Status waitForWriteConcern(OperationContext* txn,
                            const OpTime& replOpTime,
                            const WriteConcernOptions& writeConcern,
                            WriteConcernResult* result) {
-    // We assume all options have been validated earlier, if not, programming error
-    dassertOK(validateWriteConcern(txn, writeConcern));
-
     auto replCoord = repl::ReplicationCoordinator::get(txn);
 
     // Next handle blocking on disk
diff --git a/src/mongo/db/write_concern.h b/src/mongo/db/write_concern.h
index eeff284ec61..9a9720f26ee 100644
--- a/src/mongo/db/write_concern.h
+++ b/src/mongo/db/write_concern.h
@@ -52,9 +52,11 @@ StatusWith<WriteConcernOptions> extractWriteConcern(OperationContext* txn,
                                                     const bool supportsWriteConcern);
 
 /**
- * Verifies that a WriteConcern is valid for this particular host.
+ * Verifies that a WriteConcern is valid for this particular host and database.
  */
-Status validateWriteConcern(OperationContext* txn, const WriteConcernOptions& writeConcern);
+Status validateWriteConcern(OperationContext* txn,
+                            const WriteConcernOptions& writeConcern,
+                            StringData dbName);
 
 struct WriteConcernResult {
     WriteConcernResult() {