DOC: whatsnew, performance improvement in reindex non-unique

Author: morotti

doc/source/whatsnew/v2.2.0.rst

@@ -302,6 +302,7 @@ Performance improvements
 - Performance improvement in :func:`read_stata` for files with many variables (:issue:`55515`)
 - Performance improvement in :func:`to_dict` on converting DataFrame to dictionary (:issue:`50990`)
 - Performance improvement in :meth:`DataFrame.groupby` when aggregating pyarrow timestamp and duration dtypes (:issue:`55031`)
+- Performance improvement in :meth:`DataFrame.reindex` and :meth:`Series.reindex` non-unique when target is a :class:`MultiIndex` (:issue:`46235`)
 - Performance improvement in :meth:`DataFrame.sort_index` and :meth:`Series.sort_index` when indexed by a :class:`MultiIndex` (:issue:`54835`)
 - Performance improvement in :meth:`Index.difference` (:issue:`55108`)
 - Performance improvement in :meth:`Series.duplicated` for pyarrow dtypes (:issue:`55255`)