PERF-#7227: Call 'modin_frame.combine()' for merge and join only when…

… necessary (#7228)

Signed-off-by: Anatoly Myachev <[email protected]>

modin/core/storage_formats/pandas/merge.py

@@ -115,7 +115,6 @@ def row_axis_merge(cls, left, right, kwargs):
         left_index = kwargs.get("left_index", False)
         right_index = kwargs.get("right_index", False)
         sort = kwargs.get("sort", False)
-        right_to_broadcast = right._modin_frame.combine()
 
         if how in ["left", "inner"] and left_index is False and right_index is False:
             kwargs["sort"] = False
@@ -160,6 +159,7 @@ def map_func(
             elif on is not None:
                 on = list(on) if is_list_like(on) else [on]
 
+            right_to_broadcast = right._modin_frame.combine()
             new_columns, new_dtypes = cls._compute_result_metadata(
                 left, right, on, left_on, right_on, kwargs.get("suffixes", ("_x", "_y"))
             )

modin/core/storage_formats/pandas/query_compiler.py

@@ -528,13 +528,13 @@ def join(self, right, **kwargs):
         on = kwargs.get("on", None)
         how = kwargs.get("how", "left")
         sort = kwargs.get("sort", False)
-        right_to_broadcast = right._modin_frame.combine()
 
         if how in ["left", "inner"]:
 
             def map_func(left, right, kwargs=kwargs):  # pragma: no cover
                 return pandas.DataFrame.join(left, right, **kwargs)
 
+            right_to_broadcast = right._modin_frame.combine()
             new_self = self.__constructor__(
                 self._modin_frame.broadcast_apply_full_axis(
                     axis=1,