SERVER-44104 Avoid getKeySize for WiredTigerIndexCursorBase::nextKeyString on _id indexes

1 files changed, 4 insertions, 3 deletions

diff --git a/src/mongo/db/storage/wiredtiger/wiredtiger_index.cpp b/src/mongo/db/storage/wiredtiger/wiredtiger_index.cpp
index 8cfbac8622e..45f3f028766 100644
--- a/src/mongo/db/storage/wiredtiger/wiredtiger_index.cpp
+++ b/src/mongo/db/storage/wiredtiger/wiredtiger_index.cpp
@@ -1163,9 +1163,10 @@ protected:
         // and timestamp unsafe unique indexes. The contract of this function is to always return a
         // KeyString with a RecordId, so append one if it does not exists already.
         if (_idx.unique() &&
-            _key.getSize() ==
-                KeyString::getKeySize(
-                    _key.getBuffer(), _key.getSize(), _idx.getOrdering(), _typeBits)) {
+            (_idx.isIdIndex() ||
+             _key.getSize() ==
+                 KeyString::getKeySize(
+                     _key.getBuffer(), _key.getSize(), _idx.getOrdering(), _typeBits))) {
             // Create a copy of _key with a RecordId. Because _key is used during cursor restore(),
             // appending the RecordId would cause the cursor to be repositioned incorrectly.
             KeyString::Builder keyWithRecordId(_key);