void WiredTigerSnapshotManager::beginTransactionOnOplog(WiredTigerOplogManager* oplogManager,
                                                         WT_SESSION* session) const {
     invariantWTOK(session->begin_transaction(session, nullptr));
     auto rollbacker =
         MakeGuard([&] { invariant(session->rollback_transaction(session, nullptr) == 0); });

-    stdx::lock_guard<stdx::mutex> lock(_mutex);
     auto allCommittedTimestamp = oplogManager->getOplogReadTimestamp();
     invariant(Timestamp(static_cast<unsigned long long>(allCommittedTimestamp)).asULL() ==
               allCommittedTimestamp);
     auto status = setTransactionReadTimestamp(
-        Timestamp(static_cast<unsigned long long>(allCommittedTimestamp)), session);
+        Timestamp(static_cast<unsigned long long>(allCommittedTimestamp)),
+        session,
+        true /* roundToOldest */);

-    // If we failed to set the read timestamp, we assume it is due to the oldest_timestamp racing
-    // ahead.  Rather than synchronizing for this rare case, if requested, throw a
-    // WriteConflictException which will be retried.
-    if (!status.isOK() && status.code() == ErrorCodes::BadValue) {
-        throw WriteConflictException();
-    }
     fassert(50771, status);
     rollbacker.Dismiss();
}