SERVER-33336 Snapshot reads should not take MODE_IX locks when autocommit=true

1 files changed, 7 insertions, 3 deletions

diff --git a/src/mongo/db/db_raii.cpp b/src/mongo/db/db_raii.cpp
index b6fa5158000..6b9a695d02b 100644
--- a/src/mongo/db/db_raii.cpp
+++ b/src/mongo/db/db_raii.cpp
@@ -34,6 +34,7 @@
 #include "mongo/db/curop.h"
 #include "mongo/db/repl/replication_coordinator.h"
 #include "mongo/db/s/collection_sharding_state.h"
+#include "mongo/db/session_catalog.h"
 
 namespace mongo {
 namespace {
@@ -232,9 +233,12 @@ OldClientWriteContext::OldClientWriteContext(OperationContext* opCtx, StringData
 LockMode getLockModeForQuery(OperationContext* opCtx) {
     invariant(opCtx);
 
-    if (repl::ReadConcernArgs::get(opCtx).getLevel() ==
-        repl::ReadConcernLevel::kSnapshotReadConcern) {
-        return MODE_IX;
+    // Use IX locks for autocommit:false multi-statement transactions; otherwise, use IS locks.
+    if (opCtx->getWriteUnitOfWork()) {
+        invariant(OperationContextSession::get(opCtx));
+        if (!OperationContextSession::get(opCtx)->getAutocommit()) {
+            return MODE_IX;
+        }
     }
 
     return MODE_IS;