SERVER-45626: Introduce AutoGetOplog for consistent oplog locking rules

1 files changed, 26 insertions, 10 deletions

diff --git a/src/mongo/db/dbhelpers.cpp b/src/mongo/db/dbhelpers.cpp
index 47d13e8d46b..ef6c35ffe8b 100644
--- a/src/mongo/db/dbhelpers.cpp
+++ b/src/mongo/db/dbhelpers.cpp
@@ -48,11 +48,6 @@
 #include "mongo/db/query/get_executor.h"
 #include "mongo/db/query/internal_plans.h"
 #include "mongo/db/query/query_planner.h"
-#include "mongo/db/repl/repl_client_info.h"
-#include "mongo/db/repl/replication_coordinator.h"
-#include "mongo/db/service_context.h"
-#include "mongo/db/write_concern.h"
-#include "mongo/db/write_concern_options.h"
 #include "mongo/util/scopeguard.h"
 #include "mongo/util/str.h"
 
@@ -172,10 +167,28 @@ RecordId Helpers::findById(OperationContext* opCtx,
     return catalog->getEntry(desc)->accessMethod()->findSingle(opCtx, idquery["_id"].wrap());
 }
 
+// Acquires necessary locks to read the collection with the given namespace. If this is an oplog
+// read, use AutoGetOplog for simplified locking.
+Collection* getCollectionForRead(OperationContext* opCtx,
+                                 const NamespaceString& ns,
+                                 boost::optional<AutoGetCollectionForReadCommand>& autoColl,
+                                 boost::optional<AutoGetOplog>& autoOplog) {
+    if (ns.isOplog()) {
+        // Simplify locking rules for oplog collection.
+        autoOplog.emplace(opCtx, OplogAccessMode::kRead);
+        return autoOplog->getCollection();
+    } else {
+        autoColl.emplace(opCtx, NamespaceString(ns));
+        return autoColl->getCollection();
+    }
+}
+
 bool Helpers::getSingleton(OperationContext* opCtx, const char* ns, BSONObj& result) {
-    AutoGetCollectionForReadCommand ctx(opCtx, NamespaceString(ns));
-    auto exec =
-        InternalPlanner::collectionScan(opCtx, ns, ctx.getCollection(), PlanExecutor::NO_YIELD);
+    boost::optional<AutoGetCollectionForReadCommand> autoColl;
+    boost::optional<AutoGetOplog> autoOplog;
+    auto collection = getCollectionForRead(opCtx, NamespaceString(ns), autoColl, autoOplog);
+
+    auto exec = InternalPlanner::collectionScan(opCtx, ns, collection, PlanExecutor::NO_YIELD);
     PlanExecutor::ExecState state = exec->getNext(&result, nullptr);
 
     CurOp::get(opCtx)->done();
@@ -192,9 +205,12 @@ bool Helpers::getSingleton(OperationContext* opCtx, const char* ns, BSONObj& res
 }
 
 bool Helpers::getLast(OperationContext* opCtx, const char* ns, BSONObj& result) {
-    AutoGetCollectionForReadCommand autoColl(opCtx, NamespaceString(ns));
+    boost::optional<AutoGetCollectionForReadCommand> autoColl;
+    boost::optional<AutoGetOplog> autoOplog;
+    auto collection = getCollectionForRead(opCtx, NamespaceString(ns), autoColl, autoOplog);
+
     auto exec = InternalPlanner::collectionScan(
-        opCtx, ns, autoColl.getCollection(), PlanExecutor::NO_YIELD, InternalPlanner::BACKWARD);
+        opCtx, ns, collection, PlanExecutor::NO_YIELD, InternalPlanner::BACKWARD);
     PlanExecutor::ExecState state = exec->getNext(&result, nullptr);
 
     // Non-yielding collection scans from InternalPlanner will never error.