SERVER-28534 Pass collection names around as NamespaceStrings more often

Before this patch 'ns' values were often passed around as std::string or
char* containing either a dbname (no '.'), a dbname with '.$cmd', or a fully qualified
collection name. Instead pass either plain 'dbName' value (as string) or a fully
qualified name using the actual NamespaceString type.

39 files changed, 197 insertions, 198 deletions

diff --git a/src/mongo/db/auth/authorization_manager.cpp b/src/mongo/db/auth/authorization_manager.cpp
index bca15e13223..66c232813b0 100644
--- a/src/mongo/db/auth/authorization_manager.cpp
+++ b/src/mongo/db/auth/authorization_manager.cpp
@@ -629,10 +629,10 @@ Status AuthorizationManager::initialize(OperationContext* opCtx) {
 }
 
 namespace {
-bool isAuthzNamespace(StringData ns) {
-    return (ns == AuthorizationManager::rolesCollectionNamespace.ns() ||
-            ns == AuthorizationManager::usersCollectionNamespace.ns() ||
-            ns == AuthorizationManager::versionCollectionNamespace.ns());
+bool isAuthzNamespace(const NamespaceString& nss) {
+    return (nss == AuthorizationManager::rolesCollectionNamespace ||
+            nss == AuthorizationManager::usersCollectionNamespace ||
+            nss == AuthorizationManager::versionCollectionNamespace);
 }
 
 bool isAuthzCollection(StringData coll) {
@@ -641,8 +641,8 @@ bool isAuthzCollection(StringData coll) {
             coll == AuthorizationManager::versionCollectionNamespace.coll());
 }
 
-bool loggedCommandOperatesOnAuthzData(const char* ns, const BSONObj& cmdObj) {
-    if (ns != AuthorizationManager::adminCommandNamespace.ns())
+bool loggedCommandOperatesOnAuthzData(const NamespaceString& nss, const BSONObj& cmdObj) {
+    if (nss != AuthorizationManager::adminCommandNamespace)
         return false;
     const StringData cmdName(cmdObj.firstElement().fieldNameStringData());
     if (cmdName == "drop") {
@@ -661,16 +661,16 @@ bool loggedCommandOperatesOnAuthzData(const char* ns, const BSONObj& cmdObj) {
     }
 }
 
-bool appliesToAuthzData(const char* op, const char* ns, const BSONObj& o) {
+bool appliesToAuthzData(const char* op, const NamespaceString& nss, const BSONObj& o) {
     switch (*op) {
         case 'i':
         case 'u':
         case 'd':
             if (op[1] != '\0')
                 return false;  // "db" op type
-            return isAuthzNamespace(ns);
+            return isAuthzNamespace(nss);
         case 'c':
-            return loggedCommandOperatesOnAuthzData(ns, o);
+            return loggedCommandOperatesOnAuthzData(nss, o);
             break;
         case 'n':
             return false;
@@ -701,11 +701,11 @@ void AuthorizationManager::_updateCacheGeneration_inlock() {
 }
 
 void AuthorizationManager::_invalidateRelevantCacheData(const char* op,
-                                                        const char* ns,
+                                                        const NamespaceString& ns,
                                                         const BSONObj& o,
                                                         const BSONObj* o2) {
-    if (ns == AuthorizationManager::rolesCollectionNamespace.ns() ||
-        ns == AuthorizationManager::versionCollectionNamespace.ns()) {
+    if (ns == AuthorizationManager::rolesCollectionNamespace ||
+        ns == AuthorizationManager::versionCollectionNamespace) {
         invalidateUserCache();
         return;
     }
@@ -713,7 +713,7 @@ void AuthorizationManager::_invalidateRelevantCacheData(const char* op,
     if (*op == 'i' || *op == 'd' || *op == 'u') {
         // If you got into this function isAuthzNamespace() must have returned true, and we've
         // already checked that it's not the roles or version collection.
-        invariant(ns == AuthorizationManager::usersCollectionNamespace.ns());
+        invariant(ns == AuthorizationManager::usersCollectionNamespace);
 
         StatusWith<UserName> userName = (*op == 'u')
             ? extractUserNameFromIdString((*o2)["_id"].str())
@@ -732,11 +732,14 @@ void AuthorizationManager::_invalidateRelevantCacheData(const char* op,
     }
 }
 
-void AuthorizationManager::logOp(
-    OperationContext* opCtx, const char* op, const char* ns, const BSONObj& o, const BSONObj* o2) {
-    if (appliesToAuthzData(op, ns, o)) {
-        _externalState->logOp(opCtx, op, ns, o, o2);
-        _invalidateRelevantCacheData(op, ns, o, o2);
+void AuthorizationManager::logOp(OperationContext* opCtx,
+                                 const char* op,
+                                 const NamespaceString& nss,
+                                 const BSONObj& o,
+                                 const BSONObj* o2) {
+    if (appliesToAuthzData(op, nss, o)) {
+        _externalState->logOp(opCtx, op, nss, o, o2);
+        _invalidateRelevantCacheData(op, nss, o, o2);
     }
 }
 
diff --git a/src/mongo/db/auth/authorization_manager.h b/src/mongo/db/auth/authorization_manager.h
index 2532bd5217e..495bcc0aa81 100644
--- a/src/mongo/db/auth/authorization_manager.h
+++ b/src/mongo/db/auth/authorization_manager.h
@@ -303,7 +303,7 @@ public:
      */
     void logOp(OperationContext* opCtx,
                const char* opstr,
-               const char* ns,
+               const NamespaceString& nss,
                const BSONObj& obj,
                const BSONObj* patt);
 
@@ -326,7 +326,7 @@ private:
      * with oplog entries that have been pre-verified to actually affect authorization data.
      */
     void _invalidateRelevantCacheData(const char* op,
-                                      const char* ns,
+                                      const NamespaceString& ns,
                                       const BSONObj& o,
                                       const BSONObj* o2);
 
diff --git a/src/mongo/db/auth/authorization_manager_test.cpp b/src/mongo/db/auth/authorization_manager_test.cpp
index 83edae4ddef..7eb3c980e3b 100644
--- a/src/mongo/db/auth/authorization_manager_test.cpp
+++ b/src/mongo/db/auth/authorization_manager_test.cpp
@@ -456,7 +456,7 @@ public:
 TEST_F(AuthorizationManagerLogOpTest, testDropDatabaseAddsRecoveryUnits) {
     authzManager->logOp(&opCtx,
                         "c",
-                        "admin.$cmd",
+                        {"admin", "$cmd"},
                         BSON("dropDatabase"
                              << "1"),
                         nullptr);
@@ -466,7 +466,7 @@ TEST_F(AuthorizationManagerLogOpTest, testDropDatabaseAddsRecoveryUnits) {
 TEST_F(AuthorizationManagerLogOpTest, testDropAuthCollectionAddsRecoveryUnits) {
     authzManager->logOp(&opCtx,
                         "c",
-                        "admin.$cmd",
+                        {"admin", "$cmd"},
                         BSON("drop"
                              << "system.users"),
                         nullptr);
@@ -474,7 +474,7 @@ TEST_F(AuthorizationManagerLogOpTest, testDropAuthCollectionAddsRecoveryUnits) {
 
     authzManager->logOp(&opCtx,
                         "c",
-                        "admin.$cmd",
+                        {"admin", "$cmd"},
                         BSON("drop"
                              << "system.roles"),
                         nullptr);
@@ -482,7 +482,7 @@ TEST_F(AuthorizationManagerLogOpTest, testDropAuthCollectionAddsRecoveryUnits) {
 
     authzManager->logOp(&opCtx,
                         "c",
-                        "admin.$cmd",
+                        {"admin", "$cmd"},
                         BSON("drop"
                              << "system.version"),
                         nullptr);
@@ -490,7 +490,7 @@ TEST_F(AuthorizationManagerLogOpTest, testDropAuthCollectionAddsRecoveryUnits) {
 
     authzManager->logOp(&opCtx,
                         "c",
-                        "admin.$cmd",
+                        {"admin", "$cmd"},
                         BSON("drop"
                              << "system.profile"),
                         nullptr);
@@ -500,21 +500,21 @@ TEST_F(AuthorizationManagerLogOpTest, testDropAuthCollectionAddsRecoveryUnits) {
 TEST_F(AuthorizationManagerLogOpTest, testCreateAnyCollectionAddsNoRecoveryUnits) {
     authzManager->logOp(&opCtx,
                         "c",
-                        "admin.$cmd",
+                        {"admin", "$cmd"},
                         BSON("create"
                              << "system.users"),
                         nullptr);
 
     authzManager->logOp(&opCtx,
                         "c",
-                        "admin.$cmd",
+                        {"admin", "$cmd"},
                         BSON("create"
                              << "system.profile"),
                         nullptr);
 
     authzManager->logOp(&opCtx,
                         "c",
-                        "admin.$cmd",
+                        {"admin", "$cmd"},
                         BSON("create"
                              << "system.other"),
                         nullptr);
@@ -525,7 +525,7 @@ TEST_F(AuthorizationManagerLogOpTest, testCreateAnyCollectionAddsNoRecoveryUnits
 TEST_F(AuthorizationManagerLogOpTest, testRawInsertToRolesCollectionAddsRecoveryUnits) {
     authzManager->logOp(&opCtx,
                         "i",
-                        "admin.system.profile",
+                        {"admin", "system.profile"},
                         BSON("_id"
                              << "admin.user"),
                         nullptr);
@@ -533,7 +533,7 @@ TEST_F(AuthorizationManagerLogOpTest, testRawInsertToRolesCollectionAddsRecovery
 
     authzManager->logOp(&opCtx,
                         "i",
-                        "admin.system.users",
+                        {"admin", "system.users"},
                         BSON("_id"
                              << "admin.user"),
                         nullptr);
@@ -541,7 +541,7 @@ TEST_F(AuthorizationManagerLogOpTest, testRawInsertToRolesCollectionAddsRecovery
 
     authzManager->logOp(&opCtx,
                         "i",
-                        "admin.system.roles",
+                        {"admin", "system.roles"},
                         BSON("_id"
                              << "admin.user"),
                         nullptr);
diff --git a/src/mongo/db/auth/authz_manager_external_state.h b/src/mongo/db/auth/authz_manager_external_state.h
index 18277c272b2..f63e05b818f 100644
--- a/src/mongo/db/auth/authz_manager_external_state.h
+++ b/src/mongo/db/auth/authz_manager_external_state.h
@@ -157,7 +157,7 @@ public:
 
     virtual void logOp(OperationContext* opCtx,
                        const char* op,
-                       const char* ns,
+                       const NamespaceString& ns,
                        const BSONObj& o,
                        const BSONObj* o2) {}
 
diff --git a/src/mongo/db/auth/authz_manager_external_state_local.cpp b/src/mongo/db/auth/authz_manager_external_state_local.cpp
index de706dcd9da..9227e1d2dd2 100644
--- a/src/mongo/db/auth/authz_manager_external_state_local.cpp
+++ b/src/mongo/db/auth/authz_manager_external_state_local.cpp
@@ -445,13 +445,13 @@ public:
     AuthzManagerLogOpHandler(OperationContext* opCtx,
                              AuthzManagerExternalStateLocal* externalState,
                              const char* op,
-                             const char* ns,
+                             const NamespaceString& nss,
                              const BSONObj& o,
                              const BSONObj* o2)
         : _opCtx(opCtx),
           _externalState(externalState),
           _op(op),
-          _ns(ns),
+          _nss(nss),
           _o(o.getOwned()),
 
           _isO2Set(o2 ? true : false),
@@ -460,13 +460,13 @@ public:
     virtual void commit() {
         stdx::lock_guard<stdx::mutex> lk(_externalState->_roleGraphMutex);
         Status status = _externalState->_roleGraph.handleLogOp(
-            _opCtx, _op.c_str(), NamespaceString(_ns.c_str()), _o, _isO2Set ? &_o2 : NULL);
+            _opCtx, _op.c_str(), _nss, _o, _isO2Set ? &_o2 : NULL);
 
         if (status == ErrorCodes::OplogOperationUnsupported) {
             _externalState->_roleGraph = RoleGraph();
             _externalState->_roleGraphState = _externalState->roleGraphStateInitial;
             BSONObjBuilder oplogEntryBuilder;
-            oplogEntryBuilder << "op" << _op << "ns" << _ns << "o" << _o;
+            oplogEntryBuilder << "op" << _op << "ns" << _nss.ns() << "o" << _o;
             if (_isO2Set)
                 oplogEntryBuilder << "o2" << _o2;
             error() << "Unsupported modification to roles collection in oplog; "
@@ -494,19 +494,22 @@ private:
     OperationContext* _opCtx;
     AuthzManagerExternalStateLocal* _externalState;
     const std::string _op;
-    const std::string _ns;
+    const NamespaceString _nss;
     const BSONObj _o;
 
     const bool _isO2Set;
     const BSONObj _o2;
 };
 
-void AuthzManagerExternalStateLocal::logOp(
-    OperationContext* opCtx, const char* op, const char* ns, const BSONObj& o, const BSONObj* o2) {
-    if (ns == AuthorizationManager::rolesCollectionNamespace.ns() ||
-        ns == AuthorizationManager::adminCommandNamespace.ns()) {
+void AuthzManagerExternalStateLocal::logOp(OperationContext* opCtx,
+                                           const char* op,
+                                           const NamespaceString& nss,
+                                           const BSONObj& o,
+                                           const BSONObj* o2) {
+    if (nss == AuthorizationManager::rolesCollectionNamespace ||
+        nss == AuthorizationManager::adminCommandNamespace) {
         opCtx->recoveryUnit()->registerChange(
-            new AuthzManagerLogOpHandler(opCtx, this, op, ns, o, o2));
+            new AuthzManagerLogOpHandler(opCtx, this, op, nss, o, o2));
     }
 }
 
diff --git a/src/mongo/db/auth/authz_manager_external_state_local.h b/src/mongo/db/auth/authz_manager_external_state_local.h
index ccaa7e2d452..d33b8059084 100644
--- a/src/mongo/db/auth/authz_manager_external_state_local.h
+++ b/src/mongo/db/auth/authz_manager_external_state_local.h
@@ -101,7 +101,7 @@ public:
 
     virtual void logOp(OperationContext* opCtx,
                        const char* op,
-                       const char* ns,
+                       const NamespaceString& ns,
                        const BSONObj& o,
                        const BSONObj* o2);
 
diff --git a/src/mongo/db/auth/authz_manager_external_state_mock.cpp b/src/mongo/db/auth/authz_manager_external_state_mock.cpp
index ff58770d230..7b8d72ad1f7 100644
--- a/src/mongo/db/auth/authz_manager_external_state_mock.cpp
+++ b/src/mongo/db/auth/authz_manager_external_state_mock.cpp
@@ -158,7 +158,7 @@ Status AuthzManagerExternalStateMock::insert(OperationContext* opCtx,
     _documents[collectionName].push_back(toInsert);
 
     if (_authzManager) {
-        _authzManager->logOp(opCtx, "i", collectionName.ns().c_str(), toInsert, NULL);
+        _authzManager->logOp(opCtx, "i", collectionName, toInsert, NULL);
     }
 
     return Status::OK();
@@ -197,7 +197,7 @@ Status AuthzManagerExternalStateMock::updateOne(OperationContext* opCtx,
         BSONObj idQuery = driver.makeOplogEntryQuery(newObj, false);
 
         if (_authzManager) {
-            _authzManager->logOp(opCtx, "u", collectionName.ns().c_str(), logObj, &idQuery);
+            _authzManager->logOp(opCtx, "u", collectionName, logObj, &idQuery);
         }
 
         return Status::OK();
@@ -244,7 +244,7 @@ Status AuthzManagerExternalStateMock::remove(OperationContext* opCtx,
         ++n;
 
         if (_authzManager) {
-            _authzManager->logOp(opCtx, "d", collectionName.ns().c_str(), idQuery, NULL);
+            _authzManager->logOp(opCtx, "d", collectionName, idQuery, NULL);
         }
     }
     *numRemoved = n;
diff --git a/src/mongo/db/catalog/apply_ops.cpp b/src/mongo/db/catalog/apply_ops.cpp
index ca20b2b848a..b138b1f7d74 100644
--- a/src/mongo/db/catalog/apply_ops.cpp
+++ b/src/mongo/db/catalog/apply_ops.cpp
@@ -122,10 +122,11 @@ Status _applyOps(OperationContext* opCtx,
                 continue;
 
             const std::string ns = opObj["ns"].String();
+            const NamespaceString nss{ns};
 
             // Need to check this here, or OldClientContext may fail an invariant.
-            if (*opType != 'c' && !NamespaceString(ns).isValid())
-                return {ErrorCodes::InvalidNamespace, "invalid ns: " + ns};
+            if (*opType != 'c' && !nss.isValid())
+                return {ErrorCodes::InvalidNamespace, "invalid ns: " + nss.ns()};
 
             Status status(ErrorCodes::InternalError, "");
 
@@ -143,7 +144,7 @@ Status _applyOps(OperationContext* opCtx,
                 status = repl::applyOperation_inlock(opCtx, ctx.db(), opObj, alwaysUpsert);
                 if (!status.isOK())
                     return status;
-                logOpForDbHash(opCtx, ns.c_str());
+                logOpForDbHash(opCtx, nss);
             } else {
                 try {
                     // Run operations under a nested lock as a hack to prevent yielding.
@@ -186,7 +187,7 @@ Status _applyOps(OperationContext* opCtx,
                     return Status(ErrorCodes::UnknownError, ex.what());
                 }
                 WriteUnitOfWork wuow(opCtx);
-                logOpForDbHash(opCtx, ns.c_str());
+                logOpForDbHash(opCtx, nss);
                 wuow.commit();
             }
 
@@ -207,8 +208,6 @@ Status _applyOps(OperationContext* opCtx,
         // We want this applied atomically on slaves
         // so we re-wrap without the pre-condition for speed
 
-        std::string tempNS = str::stream() << dbName << ".$cmd";
-
         // TODO: possibly use mutable BSON to remove preCondition field
         // once it is available
         BSONObjBuilder cmdBuilder;
@@ -227,7 +226,7 @@ Status _applyOps(OperationContext* opCtx,
         auto opObserver = getGlobalServiceContext()->getOpObserver();
         invariant(opObserver);
         if (haveWrappingWUOW) {
-            opObserver->onApplyOps(opCtx, tempNS, cmdRewritten);
+            opObserver->onApplyOps(opCtx, dbName, cmdRewritten);
         } else {
             // When executing applyOps outside of a wrapping WriteUnitOfWOrk, always logOp the
             // command regardless of whether the individial ops succeeded and rely on any
@@ -236,7 +235,7 @@ Status _applyOps(OperationContext* opCtx,
             while (true) {
                 try {
                     WriteUnitOfWork wunit(opCtx);
-                    opObserver->onApplyOps(opCtx, tempNS, cmdRewritten);
+                    opObserver->onApplyOps(opCtx, dbName, cmdRewritten);
 
                     wunit.commit();
                     break;
diff --git a/src/mongo/db/catalog/coll_mod.cpp b/src/mongo/db/catalog/coll_mod.cpp
index a2df7e2c791..56b0287149d 100644
--- a/src/mongo/db/catalog/coll_mod.cpp
+++ b/src/mongo/db/catalog/coll_mod.cpp
@@ -345,8 +345,7 @@ Status collMod(OperationContext* opCtx,
 
         // Only observe non-view collMods, as view operations are observed as operations on the
         // system.views collection.
-        getGlobalServiceContext()->getOpObserver()->onCollMod(
-            opCtx, (dbName.toString() + ".$cmd").c_str(), cmdObj);
+        getGlobalServiceContext()->getOpObserver()->onCollMod(opCtx, nss, cmdObj);
     }
 
     wunit.commit();
diff --git a/src/mongo/db/catalog/database.h b/src/mongo/db/catalog/database.h
index a41d9dcdffb..6eedbf6b3e7 100644
--- a/src/mongo/db/catalog/database.h
+++ b/src/mongo/db/catalog/database.h
@@ -201,7 +201,7 @@ public:
 
     static Status validateDBName(StringData dbname);
 
-    const std::string& getSystemIndexesName() const {
+    const NamespaceString& getSystemIndexesName() const {
         return _indexesName;
     }
 
@@ -239,9 +239,9 @@ private:
 
     DatabaseCatalogEntry* _dbEntry;  // not owned here
 
-    const std::string _profileName;  // "dbname.system.profile"
-    const std::string _indexesName;  // "dbname.system.indexes"
-    const std::string _viewsName;    // "dbname.system.views"
+    const std::string _profileName;      // "dbname.system.profile"
+    const NamespaceString _indexesName;  // "dbname.system.indexes"
+    const std::string _viewsName;        // "dbname.system.views"
 
     int _profile;  // 0=off.
 
diff --git a/src/mongo/db/catalog/drop_database.cpp b/src/mongo/db/catalog/drop_database.cpp
index 1819f05b72d..024b097bd56 100644
--- a/src/mongo/db/catalog/drop_database.cpp
+++ b/src/mongo/db/catalog/drop_database.cpp
@@ -83,7 +83,7 @@ Status dropDatabase(OperationContext* opCtx, const std::string& dbName) {
 
         WriteUnitOfWork wunit(opCtx);
 
-        getGlobalServiceContext()->getOpObserver()->onDropDatabase(opCtx, dbName + ".$cmd");
+        getGlobalServiceContext()->getOpObserver()->onDropDatabase(opCtx, dbName);
 
         wunit.commit();
     }
diff --git a/src/mongo/db/cloner.cpp b/src/mongo/db/cloner.cpp
index 2fc1f6f0eaf..01d03fbc7bf 100644
--- a/src/mongo/db/cloner.cpp
+++ b/src/mongo/db/cloner.cpp
@@ -410,7 +410,7 @@ void Cloner::copyIndexes(OperationContext* opCtx,
     indexer.commit();
     if (opCtx->writesAreReplicated()) {
         const string targetSystemIndexesCollectionName = to_collection.getSystemIndexesCollection();
-        const char* createIndexNs = targetSystemIndexesCollectionName.c_str();
+        const NamespaceString createIndexNs{targetSystemIndexesCollectionName};
         for (auto&& infoObj : indexInfoObjs) {
             getGlobalServiceContext()->getOpObserver()->onCreateIndex(
                 opCtx, createIndexNs, infoObj, false);
diff --git a/src/mongo/db/commands.h b/src/mongo/db/commands.h
index d185c0cf6d6..0c9ffca316b 100644
--- a/src/mongo/db/commands.h
+++ b/src/mongo/db/commands.h
@@ -509,7 +509,7 @@ private:
     friend void mongo::execCommandClient(OperationContext* opCtx,
                                          Command* c,
                                          int queryOptions,
-                                         const char* ns,
+                                         StringData dbname,
                                          BSONObj& cmdObj,
                                          BSONObjBuilder& result);
 
diff --git a/src/mongo/db/commands/create_indexes.cpp b/src/mongo/db/commands/create_indexes.cpp
index 93833f09b8e..9b821a15843 100644
--- a/src/mongo/db/commands/create_indexes.cpp
+++ b/src/mongo/db/commands/create_indexes.cpp
@@ -392,7 +392,7 @@ public:
             indexer.commit();
 
             for (auto&& infoObj : indexInfoObjs) {
-                std::string systemIndexes = ns.getSystemIndexesCollection();
+                NamespaceString systemIndexes{ns.getSystemIndexesCollection()};
                 getGlobalServiceContext()->getOpObserver()->onCreateIndex(
                     opCtx, systemIndexes, infoObj, false);
             }
diff --git a/src/mongo/db/commands/dbhash.cpp b/src/mongo/db/commands/dbhash.cpp
index d1761d1f103..d633cfecd65 100644
--- a/src/mongo/db/commands/dbhash.cpp
+++ b/src/mongo/db/commands/dbhash.cpp
@@ -273,9 +273,8 @@ private:
 
 }  // namespace
 
-void logOpForDbHash(OperationContext* opCtx, const char* ns) {
-    NamespaceString nsString(ns);
-    dbhashCmd.wipeCacheForCollection(opCtx, nsString);
+void logOpForDbHash(OperationContext* opCtx, const NamespaceString& nss) {
+    dbhashCmd.wipeCacheForCollection(opCtx, nss);
 }
 
 }  // namespace mongo
diff --git a/src/mongo/db/commands/dbhash.h b/src/mongo/db/commands/dbhash.h
index 09db7e97e0e..29ec66ef9cf 100644
--- a/src/mongo/db/commands/dbhash.h
+++ b/src/mongo/db/commands/dbhash.h
@@ -31,7 +31,8 @@
 namespace mongo {
 
 class OperationContext;
+class NamespaceString;
 
-void logOpForDbHash(OperationContext* opCtx, const char* ns);
+void logOpForDbHash(OperationContext* opCtx, const NamespaceString& nss);
 
 }  // namespace mongo
diff --git a/src/mongo/db/commands/mr.cpp b/src/mongo/db/commands/mr.cpp
index 50e6edc44a5..89668c818e7 100644
--- a/src/mongo/db/commands/mr.cpp
+++ b/src/mongo/db/commands/mr.cpp
@@ -510,7 +510,7 @@ void State::prepTempCollection() {
                 uassertStatusOK(status);
             }
             // Log the createIndex operation.
-            string logNs = _config.tempNamespace.db() + ".system.indexes";
+            NamespaceString logNs{_config.tempNamespace.db(), "system.indexes"};
             getGlobalServiceContext()->getOpObserver()->onCreateIndex(_opCtx, logNs, *it, false);
         }
         wuow.commit();
diff --git a/src/mongo/db/commands_helpers.h b/src/mongo/db/commands_helpers.h
index 0f559a3af86..5880c184cdf 100644
--- a/src/mongo/db/commands_helpers.h
+++ b/src/mongo/db/commands_helpers.h
@@ -48,7 +48,7 @@ class ReplyBuilderInterface;
 void execCommandClient(OperationContext* opCtx,
                        Command* c,
                        int queryOptions,
-                       const char* ns,
+                       StringData dbname,
                        BSONObj& cmdObj,
                        BSONObjBuilder& result);
 
diff --git a/src/mongo/db/dbhelpers.cpp b/src/mongo/db/dbhelpers.cpp
index ae26b591272..c247d31a6d1 100644
--- a/src/mongo/db/dbhelpers.cpp
+++ b/src/mongo/db/dbhelpers.cpp
@@ -167,7 +167,7 @@ RecordId Helpers::findOne(OperationContext* opCtx,
 
 bool Helpers::findById(OperationContext* opCtx,
                        Database* database,
-                       const char* ns,
+                       StringData ns,
                        BSONObj query,
                        BSONObj& result,
                        bool* nsFound,
@@ -493,11 +493,11 @@ long long Helpers::removeRange(OperationContext* opCtx,
     return numDeleted;
 }
 
-void Helpers::emptyCollection(OperationContext* opCtx, const char* ns) {
-    OldClientContext context(opCtx, ns);
+void Helpers::emptyCollection(OperationContext* opCtx, const NamespaceString& nss) {
+    OldClientContext context(opCtx, nss.ns());
     repl::UnreplicatedWritesBlock uwb(opCtx);
-    Collection* collection = context.db() ? context.db()->getCollection(ns) : nullptr;
-    deleteObjects(opCtx, collection, ns, BSONObj(), PlanExecutor::YIELD_MANUAL, false);
+    Collection* collection = context.db() ? context.db()->getCollection(nss.ns()) : nullptr;
+    deleteObjects(opCtx, collection, nss, BSONObj(), PlanExecutor::YIELD_MANUAL, false);
 }
 
 Helpers::RemoveSaver::RemoveSaver(const string& a, const string& b, const string& why) {
diff --git a/src/mongo/db/dbhelpers.h b/src/mongo/db/dbhelpers.h
index 3ff0318b687..d143c418dbf 100644
--- a/src/mongo/db/dbhelpers.h
+++ b/src/mongo/db/dbhelpers.h
@@ -99,7 +99,7 @@ struct Helpers {
      */
     static bool findById(OperationContext* opCtx,
                          Database* db,
-                         const char* ns,
+                         StringData ns,
                          BSONObj query,
                          BSONObj& result,
                          bool* nsFound = 0,
@@ -184,7 +184,7 @@ struct Helpers {
      * You do not need to set the database before calling.
      * Does not oplog the operation.
      */
-    static void emptyCollection(OperationContext* opCtx, const char* ns);
+    static void emptyCollection(OperationContext* opCtx, const NamespaceString& nss);
 
     /**
      * for saving deleted bson objects to a flat file
diff --git a/src/mongo/db/exec/update.cpp b/src/mongo/db/exec/update.cpp
index 9a9b6c36a07..3dca5184810 100644
--- a/src/mongo/db/exec/update.cpp
+++ b/src/mongo/db/exec/update.cpp
@@ -666,7 +666,7 @@ BSONObj UpdateStage::transformAndUpdate(const Snapshotted<BSONObj>& oldObj, Reco
                 const RecordData oldRec(oldObj.value().objdata(), oldObj.value().objsize());
                 BSONObj idQuery = driver->makeOplogEntryQuery(newObj, request->isMulti());
                 OplogUpdateEntryArgs args;
-                args.ns = _collection->ns().ns();
+                args.nss = _collection->ns();
                 args.update = logObj;
                 args.criteria = idQuery;
                 args.fromMigrate = request->isFromMigration();
@@ -695,7 +695,7 @@ BSONObj UpdateStage::transformAndUpdate(const Snapshotted<BSONObj>& oldObj, Reco
                 invariant(_collection);
                 BSONObj idQuery = driver->makeOplogEntryQuery(newObj, request->isMulti());
                 OplogUpdateEntryArgs args;
-                args.ns = _collection->ns().ns();
+                args.nss = _collection->ns();
                 args.update = logObj;
                 args.criteria = idQuery;
                 args.fromMigrate = request->isFromMigration();
diff --git a/src/mongo/db/namespace_string-inl.h b/src/mongo/db/namespace_string-inl.h
index 1377d38ce41..c3bb251b98f 100644
--- a/src/mongo/db/namespace_string-inl.h
+++ b/src/mongo/db/namespace_string-inl.h
@@ -167,8 +167,8 @@ inline std::string NamespaceString::getSystemIndexesCollection() const {
     return db().toString() + ".system.indexes";
 }
 
-inline std::string NamespaceString::getCommandNS() const {
-    return db().toString() + ".$cmd";
+inline NamespaceString NamespaceString::getCommandNS() const {
+    return {db(), "$cmd"};
 }
 
 }  // namespace mongo
diff --git a/src/mongo/db/namespace_string.h b/src/mongo/db/namespace_string.h
index 58f26d76b2c..9a88f67a9a3 100644
--- a/src/mongo/db/namespace_string.h
+++ b/src/mongo/db/namespace_string.h
@@ -263,8 +263,8 @@ public:
     // @return db() + ".system.indexes"
     std::string getSystemIndexesCollection() const;
 
-    // @return db() + ".$cmd"
-    std::string getCommandNS() const;
+    // @return {db(), "$cmd"}
+    NamespaceString getCommandNS() const;
 
     /**
      * Function to escape most non-alpha characters from file names
diff --git a/src/mongo/db/op_observer.h b/src/mongo/db/op_observer.h
index 43142ea5cee..2cdc981bb74 100644
--- a/src/mongo/db/op_observer.h
+++ b/src/mongo/db/op_observer.h
@@ -44,7 +44,7 @@ class OperationContext;
  */
 struct OplogUpdateEntryArgs {
     // Name of the collection in which document is being updated.
-    std::string ns;
+    NamespaceString nss;
 
     // Fully updated document with damages (update modifiers) applied.
     BSONObj updatedDoc;
@@ -67,7 +67,7 @@ public:
     virtual ~OpObserver() = default;
 
     virtual void onCreateIndex(OperationContext* opCtx,
-                               const std::string& ns,
+                               const NamespaceString& ns,
                                BSONObj indexDoc,
                                bool fromMigrate) = 0;
     virtual void onInserts(OperationContext* opCtx,
@@ -98,7 +98,7 @@ public:
                                     const CollectionOptions& options,
                                     const BSONObj& idIndex) = 0;
     virtual void onCollMod(OperationContext* opCtx,
-                           const std::string& dbName,
+                           const NamespaceString& nss,
                            const BSONObj& collModCmd) = 0;
     virtual void onDropDatabase(OperationContext* opCtx, const std::string& dbName) = 0;
     virtual void onDropCollection(OperationContext* opCtx,
diff --git a/src/mongo/db/op_observer_impl.cpp b/src/mongo/db/op_observer_impl.cpp
index ea0d64f6f09..19f16cb368c 100644
--- a/src/mongo/db/op_observer_impl.cpp
+++ b/src/mongo/db/op_observer_impl.cpp
@@ -46,19 +46,18 @@
 namespace mongo {
 
 void OpObserverImpl::onCreateIndex(OperationContext* opCtx,
-                                   const std::string& ns,
+                                   const NamespaceString& ns,
                                    BSONObj indexDoc,
                                    bool fromMigrate) {
-    repl::logOp(opCtx, "i", ns.c_str(), indexDoc, nullptr, fromMigrate);
-    AuthorizationManager::get(opCtx->getServiceContext())
-        ->logOp(opCtx, "i", ns.c_str(), indexDoc, nullptr);
+    repl::logOp(opCtx, "i", ns, indexDoc, nullptr, fromMigrate);
+    AuthorizationManager::get(opCtx->getServiceContext())->logOp(opCtx, "i", ns, indexDoc, nullptr);
 
     auto css = CollectionShardingState::get(opCtx, ns);
     if (!fromMigrate) {
         css->onInsertOp(opCtx, indexDoc);
     }
 
-    logOpForDbHash(opCtx, ns.c_str());
+    logOpForDbHash(opCtx, ns);
 }
 
 void OpObserverImpl::onInserts(OperationContext* opCtx,
@@ -69,10 +68,9 @@ void OpObserverImpl::onInserts(OperationContext* opCtx,
     repl::logOps(opCtx, "i", nss, begin, end, fromMigrate);
 
     auto css = CollectionShardingState::get(opCtx, nss.ns());
-    const char* ns = nss.ns().c_str();
 
     for (auto it = begin; it != end; it++) {
-        AuthorizationManager::get(opCtx->getServiceContext())->logOp(opCtx, "i", ns, *it, nullptr);
+        AuthorizationManager::get(opCtx->getServiceContext())->logOp(opCtx, "i", nss, *it, nullptr);
         if (!fromMigrate) {
             css->onInsertOp(opCtx, *it);
         }
@@ -84,8 +82,8 @@ void OpObserverImpl::onInserts(OperationContext* opCtx,
         }
     }
 
-    logOpForDbHash(opCtx, ns);
-    if (strstr(ns, ".system.js")) {
+    logOpForDbHash(opCtx, nss);
+    if (strstr(nss.ns().c_str(), ".system.js")) {
         Scope::storedFuncMod(opCtx);
     }
     if (nss.coll() == DurableViewCatalog::viewsCollectionName()) {
@@ -99,26 +97,25 @@ void OpObserverImpl::onUpdate(OperationContext* opCtx, const OplogUpdateEntryArg
         return;
     }
 
-    repl::logOp(opCtx, "u", args.ns.c_str(), args.update, &args.criteria, args.fromMigrate);
+    repl::logOp(opCtx, "u", args.nss, args.update, &args.criteria, args.fromMigrate);
     AuthorizationManager::get(opCtx->getServiceContext())
-        ->logOp(opCtx, "u", args.ns.c_str(), args.update, &args.criteria);
+        ->logOp(opCtx, "u", args.nss, args.update, &args.criteria);
 
-    auto css = CollectionShardingState::get(opCtx, args.ns);
+    auto css = CollectionShardingState::get(opCtx, args.nss);
     if (!args.fromMigrate) {
         css->onUpdateOp(opCtx, args.updatedDoc);
     }
 
-    logOpForDbHash(opCtx, args.ns.c_str());
-    if (strstr(args.ns.c_str(), ".system.js")) {
+    logOpForDbHash(opCtx, args.nss);
+    if (strstr(args.nss.ns().c_str(), ".system.js")) {
         Scope::storedFuncMod(opCtx);
     }
 
-    NamespaceString nss(args.ns);
-    if (nss.coll() == DurableViewCatalog::viewsCollectionName()) {
-        DurableViewCatalog::onExternalChange(opCtx, nss);
+    if (args.nss.coll() == DurableViewCatalog::viewsCollectionName()) {
+        DurableViewCatalog::onExternalChange(opCtx, args.nss);
     }
 
-    if (args.ns == FeatureCompatibilityVersion::kCollection) {
+    if (args.nss.ns() == FeatureCompatibilityVersion::kCollection) {
         FeatureCompatibilityVersion::onInsertOrUpdate(args.updatedDoc);
     }
 }
@@ -139,42 +136,42 @@ CollectionShardingState::DeleteState OpObserverImpl::aboutToDelete(OperationCont
 }
 
 void OpObserverImpl::onDelete(OperationContext* opCtx,
-                              const NamespaceString& ns,
+                              const NamespaceString& nss,
                               CollectionShardingState::DeleteState deleteState,
                               bool fromMigrate) {
     if (deleteState.idDoc.isEmpty())
         return;
 
-    repl::logOp(opCtx, "d", ns.ns().c_str(), deleteState.idDoc, nullptr, fromMigrate);
+    repl::logOp(opCtx, "d", nss, deleteState.idDoc, nullptr, fromMigrate);
     AuthorizationManager::get(opCtx->getServiceContext())
-        ->logOp(opCtx, "d", ns.ns().c_str(), deleteState.idDoc, nullptr);
+        ->logOp(opCtx, "d", nss, deleteState.idDoc, nullptr);
 
-    auto css = CollectionShardingState::get(opCtx, ns.ns());
+    auto css = CollectionShardingState::get(opCtx, nss.ns());
     if (!fromMigrate) {
         css->onDeleteOp(opCtx, deleteState);
     }
 
-    logOpForDbHash(opCtx, ns.ns().c_str());
-    if (ns.coll() == "system.js") {
+    logOpForDbHash(opCtx, nss);
+    if (nss.coll() == "system.js") {
         Scope::storedFuncMod(opCtx);
     }
-    if (ns.coll() == DurableViewCatalog::viewsCollectionName()) {
-        DurableViewCatalog::onExternalChange(opCtx, ns);
+    if (nss.coll() == DurableViewCatalog::viewsCollectionName()) {
+        DurableViewCatalog::onExternalChange(opCtx, nss);
     }
-    if (ns.ns() == FeatureCompatibilityVersion::kCollection) {
+    if (nss.ns() == FeatureCompatibilityVersion::kCollection) {
         FeatureCompatibilityVersion::onDelete(deleteState.idDoc);
     }
 }
 
 void OpObserverImpl::onOpMessage(OperationContext* opCtx, const BSONObj& msgObj) {
-    repl::logOp(opCtx, "n", "", msgObj, nullptr, false);
+    repl::logOp(opCtx, "n", {}, msgObj, nullptr, false);
 }
 
 void OpObserverImpl::onCreateCollection(OperationContext* opCtx,
                                         const NamespaceString& collectionName,
                                         const CollectionOptions& options,
                                         const BSONObj& idIndex) {
-    std::string dbName = collectionName.db().toString() + ".$cmd";
+    const NamespaceString dbName = collectionName.getCommandNS();
     BSONObjBuilder b;
     b.append("create", collectionName.coll().toString());
     b.appendElements(options.toBSON());
@@ -193,49 +190,49 @@ void OpObserverImpl::onCreateCollection(OperationContext* opCtx,
 
     if (!collectionName.isSystemDotProfile()) {
         // do not replicate system.profile modifications
-        repl::logOp(opCtx, "c", dbName.c_str(), cmdObj, nullptr, false);
+        repl::logOp(opCtx, "c", dbName, cmdObj, nullptr, false);
     }
 
-    getGlobalAuthorizationManager()->logOp(opCtx, "c", dbName.c_str(), cmdObj, nullptr);
-    logOpForDbHash(opCtx, dbName.c_str());
+    getGlobalAuthorizationManager()->logOp(opCtx, "c", dbName, cmdObj, nullptr);
+    logOpForDbHash(opCtx, dbName);
 }
 
 void OpObserverImpl::onCollMod(OperationContext* opCtx,
-                               const std::string& dbName,
+                               const NamespaceString& nss,
                                const BSONObj& collModCmd) {
-    BSONElement first = collModCmd.firstElement();
-    std::string coll = first.valuestr();
+    const NamespaceString cmdNss = nss.getCommandNS();
 
-    if (!NamespaceString(NamespaceString(dbName).db(), coll).isSystemDotProfile()) {
+    if (!nss.isSystemDotProfile()) {
         // do not replicate system.profile modifications
-        repl::logOp(opCtx, "c", dbName.c_str(), collModCmd, nullptr, false);
+        repl::logOp(opCtx, "c", cmdNss, collModCmd, nullptr, false);
     }
 
-    getGlobalAuthorizationManager()->logOp(opCtx, "c", dbName.c_str(), collModCmd, nullptr);
-    logOpForDbHash(opCtx, dbName.c_str());
+    getGlobalAuthorizationManager()->logOp(opCtx, "c", cmdNss, collModCmd, nullptr);
+    logOpForDbHash(opCtx, cmdNss);
 }
 
 void OpObserverImpl::onDropDatabase(OperationContext* opCtx, const std::string& dbName) {
     BSONObj cmdObj = BSON("dropDatabase" << 1);
+    const NamespaceString cmdNss{dbName, "$cmd"};
 
-    repl::logOp(opCtx, "c", dbName.c_str(), cmdObj, nullptr, false);
+    repl::logOp(opCtx, "c", cmdNss, cmdObj, nullptr, false);
 
-    if (NamespaceString(dbName).db() == FeatureCompatibilityVersion::kDatabase) {
+    if (dbName == FeatureCompatibilityVersion::kDatabase) {
         FeatureCompatibilityVersion::onDropCollection();
     }
 
-    getGlobalAuthorizationManager()->logOp(opCtx, "c", dbName.c_str(), cmdObj, nullptr);
-    logOpForDbHash(opCtx, dbName.c_str());
+    getGlobalAuthorizationManager()->logOp(opCtx, "c", cmdNss, cmdObj, nullptr);
+    logOpForDbHash(opCtx, cmdNss);
 }
 
 void OpObserverImpl::onDropCollection(OperationContext* opCtx,
                                       const NamespaceString& collectionName) {
-    std::string dbName = collectionName.db().toString() + ".$cmd";
+    const NamespaceString dbName = collectionName.getCommandNS();
     BSONObj cmdObj = BSON("drop" << collectionName.coll().toString());
 
     if (!collectionName.isSystemDotProfile()) {
         // do not replicate system.profile modifications
-        repl::logOp(opCtx, "c", dbName.c_str(), cmdObj, nullptr, false);
+        repl::logOp(opCtx, "c", dbName, cmdObj, nullptr, false);
     }
 
     if (collectionName.coll() == DurableViewCatalog::viewsCollectionName()) {
@@ -246,12 +243,12 @@ void OpObserverImpl::onDropCollection(OperationContext* opCtx,
         FeatureCompatibilityVersion::onDropCollection();
     }
 
-    getGlobalAuthorizationManager()->logOp(opCtx, "c", dbName.c_str(), cmdObj, nullptr);
+    getGlobalAuthorizationManager()->logOp(opCtx, "c", dbName, cmdObj, nullptr);
 
     auto css = CollectionShardingState::get(opCtx, collectionName);
     css->onDropCollection(opCtx, collectionName);
 
-    logOpForDbHash(opCtx, dbName.c_str());
+    logOpForDbHash(opCtx, dbName);
 }
 
 void OpObserverImpl::onDropIndex(OperationContext* opCtx,
@@ -260,10 +257,10 @@ void OpObserverImpl::onDropIndex(OperationContext* opCtx,
                                  const BSONObj& indexInfo) {
     BSONObj cmdObj = BSON("dropIndexes" << ns.coll() << "index" << indexName);
     auto commandNS = ns.getCommandNS();
-    repl::logOp(opCtx, "c", commandNS.c_str(), cmdObj, &indexInfo, false);
+    repl::logOp(opCtx, "c", commandNS, cmdObj, &indexInfo, false);
 
-    getGlobalAuthorizationManager()->logOp(opCtx, "c", commandNS.c_str(), cmdObj, &indexInfo);
-    logOpForDbHash(opCtx, commandNS.c_str());
+    getGlobalAuthorizationManager()->logOp(opCtx, "c", commandNS, cmdObj, &indexInfo);
+    logOpForDbHash(opCtx, commandNS);
 }
 
 void OpObserverImpl::onRenameCollection(OperationContext* opCtx,
@@ -271,59 +268,60 @@ void OpObserverImpl::onRenameCollection(OperationContext* opCtx,
                                         const NamespaceString& toCollection,
                                         bool dropTarget,
                                         bool stayTemp) {
-    std::string dbName = fromCollection.db().toString() + ".$cmd";
+    const NamespaceString cmdNss = fromCollection.getCommandNS();
     BSONObj cmdObj =
         BSON("renameCollection" << fromCollection.ns() << "to" << toCollection.ns() << "stayTemp"
                                 << stayTemp
                                 << "dropTarget"
                                 << dropTarget);
 
-    repl::logOp(opCtx, "c", dbName.c_str(), cmdObj, nullptr, false);
+    repl::logOp(opCtx, "c", cmdNss, cmdObj, nullptr, false);
     if (fromCollection.coll() == DurableViewCatalog::viewsCollectionName() ||
         toCollection.coll() == DurableViewCatalog::viewsCollectionName()) {
         DurableViewCatalog::onExternalChange(
             opCtx, NamespaceString(DurableViewCatalog::viewsCollectionName()));
     }
 
-    getGlobalAuthorizationManager()->logOp(opCtx, "c", dbName.c_str(), cmdObj, nullptr);
-    logOpForDbHash(opCtx, dbName.c_str());
+    getGlobalAuthorizationManager()->logOp(opCtx, "c", cmdNss, cmdObj, nullptr);
+    logOpForDbHash(opCtx, cmdNss);
 }
 
 void OpObserverImpl::onApplyOps(OperationContext* opCtx,
                                 const std::string& dbName,
                                 const BSONObj& applyOpCmd) {
-    repl::logOp(opCtx, "c", dbName.c_str(), applyOpCmd, nullptr, false);
+    const NamespaceString cmdNss{dbName, "$cmd"};
+    repl::logOp(opCtx, "c", cmdNss, applyOpCmd, nullptr, false);
 
-    getGlobalAuthorizationManager()->logOp(opCtx, "c", dbName.c_str(), applyOpCmd, nullptr);
-    logOpForDbHash(opCtx, dbName.c_str());
+    getGlobalAuthorizationManager()->logOp(opCtx, "c", cmdNss, applyOpCmd, nullptr);
+    logOpForDbHash(opCtx, cmdNss);
 }
 
 void OpObserverImpl::onConvertToCapped(OperationContext* opCtx,
                                        const NamespaceString& collectionName,
                                        double size) {
-    std::string dbName = collectionName.db().toString() + ".$cmd";
+    const NamespaceString cmdNss = collectionName.getCommandNS();
     BSONObj cmdObj = BSON("convertToCapped" << collectionName.coll() << "size" << size);
 
     if (!collectionName.isSystemDotProfile()) {
         // do not replicate system.profile modifications
-        repl::logOp(opCtx, "c", dbName.c_str(), cmdObj, nullptr, false);
+        repl::logOp(opCtx, "c", cmdNss, cmdObj, nullptr, false);
     }
 
-    getGlobalAuthorizationManager()->logOp(opCtx, "c", dbName.c_str(), cmdObj, nullptr);
-    logOpForDbHash(opCtx, dbName.c_str());
+    getGlobalAuthorizationManager()->logOp(opCtx, "c", cmdNss, cmdObj, nullptr);
+    logOpForDbHash(opCtx, cmdNss);
 }
 
 void OpObserverImpl::onEmptyCapped(OperationContext* opCtx, const NamespaceString& collectionName) {
-    std::string dbName = collectionName.db().toString() + ".$cmd";
+    const NamespaceString cmdNss = collectionName.getCommandNS();
     BSONObj cmdObj = BSON("emptycapped" << collectionName.coll());
 
     if (!collectionName.isSystemDotProfile()) {
         // do not replicate system.profile modifications
-        repl::logOp(opCtx, "c", dbName.c_str(), cmdObj, nullptr, false);
+        repl::logOp(opCtx, "c", cmdNss, cmdObj, nullptr, false);
     }
 
-    getGlobalAuthorizationManager()->logOp(opCtx, "c", dbName.c_str(), cmdObj, nullptr);
-    logOpForDbHash(opCtx, dbName.c_str());
+    getGlobalAuthorizationManager()->logOp(opCtx, "c", cmdNss, cmdObj, nullptr);
+    logOpForDbHash(opCtx, cmdNss);
 }
 
 }  // namespace mongo
diff --git a/src/mongo/db/op_observer_impl.h b/src/mongo/db/op_observer_impl.h
index b02b7c96955..28e08a3f0b1 100644
--- a/src/mongo/db/op_observer_impl.h
+++ b/src/mongo/db/op_observer_impl.h
@@ -40,7 +40,7 @@ public:
     virtual ~OpObserverImpl() = default;
 
     void onCreateIndex(OperationContext* opCtx,
-                       const std::string& ns,
+                       const NamespaceString& ns,
                        BSONObj indexDoc,
                        bool fromMigrate) override;
     void onInserts(OperationContext* opCtx,
@@ -62,7 +62,7 @@ public:
                             const CollectionOptions& options,
                             const BSONObj& idIndex) override;
     void onCollMod(OperationContext* opCtx,
-                   const std::string& dbName,
+                   const NamespaceString& nss,
                    const BSONObj& collModCmd) override;
     void onDropDatabase(OperationContext* opCtx, const std::string& dbName) override;
     void onDropCollection(OperationContext* opCtx, const NamespaceString& collectionName) override;
diff --git a/src/mongo/db/op_observer_noop.cpp b/src/mongo/db/op_observer_noop.cpp
index 93404bd0ccc..426df480b13 100644
--- a/src/mongo/db/op_observer_noop.cpp
+++ b/src/mongo/db/op_observer_noop.cpp
@@ -32,7 +32,7 @@
 
 namespace mongo {
 
-void OpObserverNoop::onCreateIndex(OperationContext*, const std::string&, BSONObj, bool) {}
+void OpObserverNoop::onCreateIndex(OperationContext*, const NamespaceString&, BSONObj, bool) {}
 
 void OpObserverNoop::onInserts(OperationContext*,
                                const NamespaceString&,
@@ -60,7 +60,7 @@ void OpObserverNoop::onCreateCollection(OperationContext*,
                                         const CollectionOptions&,
                                         const BSONObj&) {}
 
-void OpObserverNoop::onCollMod(OperationContext*, const std::string&, const BSONObj&) {}
+void OpObserverNoop::onCollMod(OperationContext*, const NamespaceString&, const BSONObj&) {}
 
 void OpObserverNoop::onDropDatabase(OperationContext*, const std::string&) {}
 
diff --git a/src/mongo/db/op_observer_noop.h b/src/mongo/db/op_observer_noop.h
index 675fff217f5..490c7457cdd 100644
--- a/src/mongo/db/op_observer_noop.h
+++ b/src/mongo/db/op_observer_noop.h
@@ -40,7 +40,7 @@ public:
     virtual ~OpObserverNoop() = default;
 
     void onCreateIndex(OperationContext* opCtx,
-                       const std::string& ns,
+                       const NamespaceString& ns,
                        BSONObj indexDoc,
                        bool fromMigrate) override;
     void onInserts(OperationContext* opCtx,
@@ -62,7 +62,7 @@ public:
                             const CollectionOptions& options,
                             const BSONObj& idIndex) override;
     void onCollMod(OperationContext* opCtx,
-                   const std::string& dbName,
+                   const NamespaceString& dbName,
                    const BSONObj& collModCmd) override;
     void onDropDatabase(OperationContext* opCtx, const std::string& dbName) override;
     void onDropCollection(OperationContext* opCtx, const NamespaceString& collectionName) override;
diff --git a/src/mongo/db/ops/delete.cpp b/src/mongo/db/ops/delete.cpp
index 636a9aa17ee..19fc3eb7458 100644
--- a/src/mongo/db/ops/delete.cpp
+++ b/src/mongo/db/ops/delete.cpp
@@ -46,14 +46,13 @@ namespace mongo {
 */
 long long deleteObjects(OperationContext* opCtx,
                         Collection* collection,
-                        StringData ns,
+                        const NamespaceString& ns,
                         BSONObj pattern,
                         PlanExecutor::YieldPolicy policy,
                         bool justOne,
                         bool god,
                         bool fromMigrate) {
-    NamespaceString nsString(ns);
-    DeleteRequest request(nsString);
+    DeleteRequest request(ns);
     request.setQuery(pattern);
     request.setMulti(!justOne);
     request.setGod(god);
diff --git a/src/mongo/db/ops/delete.h b/src/mongo/db/ops/delete.h
index bead641a0b8..bb7427f5bb5 100644
--- a/src/mongo/db/ops/delete.h
+++ b/src/mongo/db/ops/delete.h
@@ -41,7 +41,7 @@ class OperationContext;
 
 long long deleteObjects(OperationContext* opCtx,
                         Collection* collection,
-                        StringData ns,
+                        const NamespaceString& ns,
                         BSONObj pattern,
                         PlanExecutor::YieldPolicy policy,
                         bool justOne,
diff --git a/src/mongo/db/repl/master_slave.cpp b/src/mongo/db/repl/master_slave.cpp
index e6e4f99a883..163de670c0d 100644
--- a/src/mongo/db/repl/master_slave.cpp
+++ b/src/mongo/db/repl/master_slave.cpp
@@ -199,7 +199,7 @@ void ReplSource::ensureMe(OperationContext* opCtx) {
         Lock::DBLock dblk(opCtx, "local", MODE_X);
         WriteUnitOfWork wunit(opCtx);
         // clean out local.me
-        Helpers::emptyCollection(opCtx, "local.me");
+        Helpers::emptyCollection(opCtx, NamespaceString("local.me"));
 
         // repopulate
         BSONObjBuilder b;
diff --git a/src/mongo/db/repl/oplog.cpp b/src/mongo/db/repl/oplog.cpp
index 51a44a672ed..fd32b0beae7 100644
--- a/src/mongo/db/repl/oplog.cpp
+++ b/src/mongo/db/repl/oplog.cpp
@@ -390,13 +390,12 @@ void _logOpsInner(OperationContext* opCtx,
 
 void logOp(OperationContext* opCtx,
            const char* opstr,
-           const char* ns,
+           const NamespaceString& nss,
            const BSONObj& obj,
            const BSONObj* o2,
            bool fromMigrate) {
     ReplicationCoordinator::Mode replMode =
         ReplicationCoordinator::get(opCtx)->getReplicationMode();
-    NamespaceString nss(ns);
     if (oplogDisabled(opCtx, replMode, nss))
         return;
 
@@ -705,6 +704,7 @@ Status applyOperation_inlock(OperationContext* opCtx,
             "'ns' must be of type String",
             fieldNs.type() == BSONType::String);
     const StringData ns = fieldNs.valueStringData();
+    NamespaceString requestNss{ns};
 
     BSONObj o2;
     if (fieldO2.isABSONObj())
@@ -885,13 +885,12 @@ Status applyOperation_inlock(OperationContext* opCtx,
                 BSONObjBuilder b;
                 b.append(o.getField("_id"));
 
-                const NamespaceString requestNs(ns);
-                UpdateRequest request(requestNs);
+                UpdateRequest request(requestNss);
 
                 request.setQuery(b.done());
                 request.setUpdates(o);
                 request.setUpsert();
-                UpdateLifecycleImpl updateLifecycle(requestNs);
+                UpdateLifecycleImpl updateLifecycle(requestNss);
                 request.setLifecycle(&updateLifecycle);
 
                 UpdateResult res = update(opCtx, db, request);
@@ -916,13 +915,12 @@ Status applyOperation_inlock(OperationContext* opCtx,
                 str::stream() << "Failed to apply update due to missing _id: " << op.toString(),
                 updateCriteria.hasField("_id"));
 
-        const NamespaceString requestNs(ns);
-        UpdateRequest request(requestNs);
+        UpdateRequest request(requestNss);
 
         request.setQuery(updateCriteria);
         request.setUpdates(o);
         request.setUpsert(upsert);
-        UpdateLifecycleImpl updateLifecycle(requestNs);
+        UpdateLifecycleImpl updateLifecycle(requestNss);
         request.setLifecycle(&updateLifecycle);
 
         UpdateResult ur = update(opCtx, db, request);
@@ -976,7 +974,8 @@ Status applyOperation_inlock(OperationContext* opCtx,
                 o.hasField("_id"));
 
         if (opType[1] == 0) {
-            deleteObjects(opCtx, collection, ns, o, PlanExecutor::YIELD_MANUAL, /*justOne*/ valueB);
+            deleteObjects(
+                opCtx, collection, requestNss, o, PlanExecutor::YIELD_MANUAL, /*justOne*/ valueB);
         } else
             verify(opType[1] == 'b');  // "db" advertisement
         if (incrementOpsAppliedStats) {
@@ -999,7 +998,7 @@ Status applyOperation_inlock(OperationContext* opCtx,
     // observers.
     WriteUnitOfWork wuow(opCtx);
     getGlobalAuthorizationManager()->logOp(
-        opCtx, opType, ns.toString().c_str(), o, fieldO2.isABSONObj() ? &o2 : NULL);
+        opCtx, opType, requestNss, o, fieldO2.isABSONObj() ? &o2 : NULL);
     wuow.commit();
 
     return Status::OK();
@@ -1115,7 +1114,7 @@ Status applyCommand_inlock(OperationContext* opCtx,
     // AuthorizationManager's logOp method registers a RecoveryUnit::Change
     // and to do so we need to have begun a UnitOfWork
     WriteUnitOfWork wuow(opCtx);
-    getGlobalAuthorizationManager()->logOp(opCtx, opType, nss.ns().c_str(), o, nullptr);
+    getGlobalAuthorizationManager()->logOp(opCtx, opType, nss, o, nullptr);
     wuow.commit();
 
     return Status::OK();
diff --git a/src/mongo/db/repl/oplog.h b/src/mongo/db/repl/oplog.h
index fcff70fb607..782a15a1725 100644
--- a/src/mongo/db/repl/oplog.h
+++ b/src/mongo/db/repl/oplog.h
@@ -93,7 +93,7 @@ void logOps(OperationContext* opCtx,
  */
 void logOp(OperationContext* opCtx,
            const char* opstr,
-           const char* ns,
+           const NamespaceString& ns,
            const BSONObj& obj,
            const BSONObj* o2,
            bool fromMigrate);
diff --git a/src/mongo/db/repl/replication_coordinator_external_state_impl.cpp b/src/mongo/db/repl/replication_coordinator_external_state_impl.cpp
index 5025269fa4e..925704e7f84 100644
--- a/src/mongo/db/repl/replication_coordinator_external_state_impl.cpp
+++ b/src/mongo/db/repl/replication_coordinator_external_state_impl.cpp
@@ -427,7 +427,7 @@ OID ReplicationCoordinatorExternalStateImpl::ensureMe(OperationContext* opCtx) {
             myRID = OID::gen();
 
             // clean out local.me
-            Helpers::emptyCollection(opCtx, meCollectionName);
+            Helpers::emptyCollection(opCtx, NamespaceString(meCollectionName));
 
             // repopulate
             BSONObjBuilder b;
diff --git a/src/mongo/db/repl/rs_rollback.cpp b/src/mongo/db/repl/rs_rollback.cpp
index d32404132e4..b17e80c6035 100644
--- a/src/mongo/db/repl/rs_rollback.cpp
+++ b/src/mongo/db/repl/rs_rollback.cpp
@@ -718,7 +718,7 @@ void syncFixUp(OperationContext* opCtx,
                         } else {
                             deleteObjects(opCtx,
                                           collection,
-                                          doc.ns,
+                                          docNss,
                                           pattern,
                                           PlanExecutor::YIELD_MANUAL,
                                           true,   // justone
@@ -729,14 +729,13 @@ void syncFixUp(OperationContext* opCtx,
                     // TODO faster...
                     updates++;
 
-                    const NamespaceString requestNs(doc.ns);
-                    UpdateRequest request(requestNs);
+                    UpdateRequest request(docNss);
 
                     request.setQuery(pattern);
                     request.setUpdates(idAndDoc.second);
                     request.setGod();
                     request.setUpsert();
-                    UpdateLifecycleImpl updateLifecycle(requestNs);
+                    UpdateLifecycleImpl updateLifecycle(docNss);
                     request.setLifecycle(&updateLifecycle);
 
                     update(opCtx, ctx.db(), request);
diff --git a/src/mongo/db/repl/sync_tail_test.cpp b/src/mongo/db/repl/sync_tail_test.cpp
index 2fe5ea8b8d4..5ce737f5d11 100644
--- a/src/mongo/db/repl/sync_tail_test.cpp
+++ b/src/mongo/db/repl/sync_tail_test.cpp
@@ -200,7 +200,7 @@ OplogEntry makeCommandOplogEntry(OpTime opTime,
     bob.append("h", 1LL);
     bob.append("v", 2);
     bob.append("op", "c");
-    bob.append("ns", nss.getCommandNS());
+    bob.append("ns", nss.getCommandNS().ns());
     bob.append("o", command);
     return OplogEntry(bob.obj());
 }
diff --git a/src/mongo/db/s/migration_destination_manager.cpp b/src/mongo/db/s/migration_destination_manager.cpp
index e9cc1fff46b..2f9355dcdd4 100644
--- a/src/mongo/db/s/migration_destination_manager.cpp
+++ b/src/mongo/db/s/migration_destination_manager.cpp
@@ -121,7 +121,7 @@ bool isInRange(const BSONObj& obj,
  * TODO: Could optimize this check out if sharding on _id.
  */
 bool willOverrideLocalId(OperationContext* opCtx,
-                         const string& ns,
+                         const NamespaceString& nss,
                          BSONObj min,
                          BSONObj max,
                          BSONObj shardKeyPattern,
@@ -129,7 +129,7 @@ bool willOverrideLocalId(OperationContext* opCtx,
                          BSONObj remoteDoc,
                          BSONObj* localDoc) {
     *localDoc = BSONObj();
-    if (Helpers::findById(opCtx, db, ns.c_str(), remoteDoc, *localDoc)) {
+    if (Helpers::findById(opCtx, db, nss.ns(), remoteDoc, *localDoc)) {
         return !isInRange(*localDoc, min, max, shardKeyPattern);
     }
 
@@ -670,7 +670,7 @@ void MigrationDestinationManager::_migrateDriver(OperationContext* opCtx,
 
                     BSONObj localDoc;
                     if (willOverrideLocalId(opCtx,
-                                            _nss.ns(),
+                                            _nss,
                                             min,
                                             max,
                                             shardKeyPattern,
@@ -746,7 +746,7 @@ void MigrationDestinationManager::_migrateDriver(OperationContext* opCtx,
                 break;
             }
 
-            _applyMigrateOp(opCtx, _nss.ns(), min, max, shardKeyPattern, res, &lastOpApplied);
+            _applyMigrateOp(opCtx, _nss, min, max, shardKeyPattern, res, &lastOpApplied);
 
             const int maxIterations = 3600 * 50;
 
@@ -837,7 +837,7 @@ void MigrationDestinationManager::_migrateDriver(OperationContext* opCtx,
             }
 
             if (res["size"].number() > 0 &&
-                _applyMigrateOp(opCtx, _nss.ns(), min, max, shardKeyPattern, res, &lastOpApplied)) {
+                _applyMigrateOp(opCtx, _nss, min, max, shardKeyPattern, res, &lastOpApplied)) {
                 continue;
             }
 
@@ -879,7 +879,7 @@ void MigrationDestinationManager::_migrateDriver(OperationContext* opCtx,
 }
 
 bool MigrationDestinationManager::_applyMigrateOp(OperationContext* opCtx,
-                                                  const string& ns,
+                                                  const NamespaceString& nss,
                                                   const BSONObj& min,
                                                   const BSONObj& max,
                                                   const BSONObj& shardKeyPattern,
@@ -893,19 +893,19 @@ bool MigrationDestinationManager::_applyMigrateOp(OperationContext* opCtx,
     bool didAnything = false;
 
     if (xfer["deleted"].isABSONObj()) {
-        Lock::DBLock dlk(opCtx, nsToDatabaseSubstring(ns), MODE_IX);
-        Helpers::RemoveSaver rs("moveChunk", ns, "removedDuring");
+        Lock::DBLock dlk(opCtx, nss.db(), MODE_IX);
+        Helpers::RemoveSaver rs("moveChunk", nss.ns(), "removedDuring");
 
         BSONObjIterator i(xfer["deleted"].Obj());  // deleted documents
         while (i.more()) {
-            Lock::CollectionLock clk(opCtx->lockState(), ns, MODE_X);
-            OldClientContext ctx(opCtx, ns);
+            Lock::CollectionLock clk(opCtx->lockState(), nss.ns(), MODE_X);
+            OldClientContext ctx(opCtx, nss.ns());
 
             BSONObj id = i.next().Obj();
 
             // do not apply delete if doc does not belong to the chunk being migrated
             BSONObj fullObj;
-            if (Helpers::findById(opCtx, ctx.db(), ns.c_str(), id, fullObj)) {
+            if (Helpers::findById(opCtx, ctx.db(), nss.ns(), id, fullObj)) {
                 if (!isInRange(fullObj, min, max, shardKeyPattern)) {
                     if (MONGO_FAIL_POINT(failMigrationReceivedOutOfRangeOperation)) {
                         invariant(0);
@@ -919,8 +919,8 @@ bool MigrationDestinationManager::_applyMigrateOp(OperationContext* opCtx,
             }
 
             deleteObjects(opCtx,
-                          ctx.db() ? ctx.db()->getCollection(ns) : nullptr,
-                          ns,
+                          ctx.db() ? ctx.db()->getCollection(nss.ns()) : nullptr,
+                          nss,
                           id,
                           PlanExecutor::YIELD_MANUAL,
                           true /* justOne */,
@@ -935,7 +935,7 @@ bool MigrationDestinationManager::_applyMigrateOp(OperationContext* opCtx,
     if (xfer["reload"].isABSONObj()) {  // modified documents (insert/update)
         BSONObjIterator i(xfer["reload"].Obj());
         while (i.more()) {
-            OldClientWriteContext cx(opCtx, ns);
+            OldClientWriteContext cx(opCtx, nss.ns());
 
             BSONObj updatedDoc = i.next().Obj();
 
@@ -949,7 +949,7 @@ bool MigrationDestinationManager::_applyMigrateOp(OperationContext* opCtx,
 
             BSONObj localDoc;
             if (willOverrideLocalId(
-                    opCtx, ns, min, max, shardKeyPattern, cx.db(), updatedDoc, &localDoc)) {
+                    opCtx, nss, min, max, shardKeyPattern, cx.db(), updatedDoc, &localDoc)) {
                 string errMsg = str::stream() << "cannot migrate chunk, local document " << localDoc
                                               << " has same _id as reloaded remote document "
                                               << updatedDoc;
@@ -961,7 +961,7 @@ bool MigrationDestinationManager::_applyMigrateOp(OperationContext* opCtx,
             }
 
             // We are in write lock here, so sure we aren't killing
-            Helpers::upsert(opCtx, ns, updatedDoc, true);
+            Helpers::upsert(opCtx, nss.ns(), updatedDoc, true);
 
             *lastOpApplied = repl::ReplClientInfo::forClient(opCtx->getClient()).getLastOp();
             didAnything = true;
diff --git a/src/mongo/db/s/migration_destination_manager.h b/src/mongo/db/s/migration_destination_manager.h
index 700e9284159..c42ce1cdcb2 100644
--- a/src/mongo/db/s/migration_destination_manager.h
+++ b/src/mongo/db/s/migration_destination_manager.h
@@ -134,7 +134,7 @@ private:
                         const WriteConcernOptions& writeConcern);
 
     bool _applyMigrateOp(OperationContext* opCtx,
-                         const std::string& ns,
+                         const NamespaceString& ns,
                          const BSONObj& min,
                          const BSONObj& max,
                          const BSONObj& shardKeyPattern,
diff --git a/src/mongo/db/views/durable_view_catalog.cpp b/src/mongo/db/views/durable_view_catalog.cpp
index 757952ec598..dff65bbb9a5 100644
--- a/src/mongo/db/views/durable_view_catalog.cpp
+++ b/src/mongo/db/views/durable_view_catalog.cpp
@@ -148,7 +148,7 @@ void DurableViewCatalogImpl::upsert(OperationContext* opCtx,
             systemViews->insertDocument(opCtx, view, &CurOp::get(opCtx)->debug(), enforceQuota));
     } else {
         OplogUpdateEntryArgs args;
-        args.ns = systemViewsNs.ns();
+        args.nss = systemViewsNs;
         args.update = view;
         args.criteria = BSON("_id" << name.ns());
         args.fromMigrate = false;