SERVER-36437 Use MODE_IS for dbstats

(cherry picked from commit 091ef080cdcfcbed720a536e57f5afd9b8a54b46)

2 files changed, 9 insertions, 12 deletions

diff --git a/src/mongo/db/catalog/database_impl.cpp b/src/mongo/db/catalog/database_impl.cpp
index 626df16fad8..989e00ff5db 100644
--- a/src/mongo/db/catalog/database_impl.cpp
+++ b/src/mongo/db/catalog/database_impl.cpp
@@ -269,8 +269,7 @@ void DatabaseImpl::init(OperationContext* const opCtx) {
     list<string> collections;
     _dbEntry->getCollectionNamespaces(&collections);
 
-    for (list<string>::const_iterator it = collections.begin(); it != collections.end(); ++it) {
-        const string ns = *it;
+    for (auto ns : collections) {
         NamespaceString nss(ns);
         _collections[ns] = _getOrCreateCollectionInstance(opCtx, nss);
     }
@@ -295,8 +294,7 @@ void DatabaseImpl::clearTmpCollections(OperationContext* opCtx) {
     list<string> collections;
     _dbEntry->getCollectionNamespaces(&collections);
 
-    for (list<string>::iterator i = collections.begin(); i != collections.end(); ++i) {
-        string ns = *i;
+    for (auto ns : collections) {
         invariant(NamespaceString::normal(ns));
 
         CollectionCatalogEntry* coll = _dbEntry->getCollectionCatalogEntry(ns);
@@ -367,8 +365,6 @@ bool DatabaseImpl::isDropPending(OperationContext* opCtx) const {
 }
 
 void DatabaseImpl::getStats(OperationContext* opCtx, BSONObjBuilder* output, double scale) {
-    list<string> collections;
-    _dbEntry->getCollectionNamespaces(&collections);
 
     long long nCollections = 0;
     long long nViews = 0;
@@ -379,9 +375,13 @@ void DatabaseImpl::getStats(OperationContext* opCtx, BSONObjBuilder* output, dou
     long long indexes = 0;
     long long indexSize = 0;
 
-    for (list<string>::const_iterator it = collections.begin(); it != collections.end(); ++it) {
-        const string ns = *it;
+    invariant(opCtx->lockState()->isDbLockedForMode(name(), MODE_IS));
+    list<string> collections;
+    _dbEntry->getCollectionNamespaces(&collections);
+
 
+    for (auto ns : collections) {
+        Lock::CollectionLock colLock(opCtx->lockState(), ns, MODE_IS);
         Collection* collection = getCollection(opCtx, ns);
 
         if (!collection)
diff --git a/src/mongo/db/commands/dbcommands.cpp b/src/mongo/db/commands/dbcommands.cpp
index 98920e2ee30..261b332fc7d 100644
--- a/src/mongo/db/commands/dbcommands.cpp
+++ b/src/mongo/db/commands/dbcommands.cpp
@@ -1039,10 +1039,7 @@ public:
             CurOp::get(opCtx)->setNS_inlock(dbname);
         }
 
-        // We lock the entire database in S-mode in order to ensure that the contents will not
-        // change for the stats snapshot. This might be unnecessary and if it becomes a
-        // performance issue, we can take IS lock and then lock collection-by-collection.
-        AutoGetDb autoDb(opCtx, ns, MODE_S);
+        AutoGetDb autoDb(opCtx, ns, MODE_IS);
 
         result.append("db", ns);