FEAT-#7337: Using dynamic partitionning in broadcast_apply (#7338)

Signed-off-by: Kirill Suvorov <kirill.suvorov@intel.com>

modin/core/dataframe/algebra/groupby.py

@@ -655,9 +655,11 @@ def aggregate_on_dict(grp_obj, *args, **kwargs):
                     )
 
             native_res_part = [] if native_agg_res is None else [native_agg_res]
-            result = pandas.concat(
-                [*native_res_part, *custom_results], axis=1, copy=False
-            )
+            parts = [*native_res_part, *custom_results]
+            if parts:
+                result = pandas.concat(parts, axis=1, copy=False)
+            else:
+                result = pandas.DataFrame(columns=result_columns)
 
             # The order is naturally preserved if there's no custom aggregations
             if preserve_aggregation_order and len(custom_aggs):

modin/core/dataframe/pandas/partitioning/partition_manager.py

@@ -440,7 +440,7 @@ def get_partitions(index):
 
     @classmethod
     @wait_computations_if_benchmark_mode
-    def broadcast_apply(cls, axis, apply_func, left, right):
+    def base_broadcast_apply(cls, axis, apply_func, left, right):
         """
         Broadcast the `right` partitions to `left` and apply `apply_func` function.
 
@@ -504,6 +504,7 @@ def broadcast_axis_partitions(
         keep_partitioning=False,
         num_splits=None,
         apply_indices=None,
+        broadcast_all=True,
         enumerate_partitions=False,
         lengths=None,
         apply_func_args=None,
@@ -532,6 +533,8 @@ def broadcast_axis_partitions(
             then the number of splits is preserved.
         apply_indices : list of ints, default: None
             Indices of `axis ^ 1` to apply function over.
+        broadcast_all : bool, default: True
+            Whether or not to pass all right axis partitions to each of the left axis partitions.
         enumerate_partitions : bool, default: False
             Whether or not to pass partition index into `apply_func`.
             Note that `apply_func` must be able to accept `partition_idx` kwarg.
@@ -578,7 +581,6 @@ def broadcast_axis_partitions(
         # load-balance the data as well.
         kw = {
             "num_splits": num_splits,
-            "other_axis_partition": right_partitions,
             "maintain_partitioning": keep_partitioning,
         }
         if lengths:
@@ -593,6 +595,9 @@ def broadcast_axis_partitions(
                 left_partitions[i].apply(
                     preprocessed_map_func,
                     *(apply_func_args if apply_func_args else []),
+                    other_axis_partition=(
+                        right_partitions if broadcast_all else right_partitions[i]
+                    ),
                     **kw,
                     **({"partition_idx": idx} if enumerate_partitions else {}),
                     **kwargs,
@@ -648,6 +653,56 @@ def base_map_partitions(
             ]
         )
 
+    @classmethod
+    @wait_computations_if_benchmark_mode
+    def broadcast_apply(
+        cls,
+        axis,
+        apply_func,
+        left,
+        right,
+    ):
+        """
+        Broadcast the `right` partitions to `left` and apply `apply_func` function using different approaches to achieve the best performance.
+
+        Parameters
+        ----------
+        axis : {0, 1}
+            Axis to apply and broadcast over.
+        apply_func : callable
+            Function to apply.
+        left : np.ndarray
+            NumPy array of left partitions.
+        right : np.ndarray
+            NumPy array of right partitions.
+
+        Returns
+        -------
+        np.ndarray
+            NumPy array of result partition objects.
+        """
+        if not DynamicPartitioning.get():
+            # block-wise broadcast
+            new_partitions = cls.base_broadcast_apply(
+                axis,
+                apply_func,
+                left,
+                right,
+            )
+        else:
+            # The dynamic partitioning behavior of `broadcast_apply` differs from that of `map_partitions`,
+            # since the columnar approach for `broadcast_apply` results in slowdown.
+            # axis-wise broadcast
+            new_partitions = cls.broadcast_axis_partitions(
+                axis=axis ^ 1,
+                left=left,
+                right=right,
+                apply_func=apply_func,
+                broadcast_all=False,
+                keep_partitioning=True,
+            )
+        return new_partitions
+
     @classmethod
     @wait_computations_if_benchmark_mode
     def map_partitions(

modin/core/storage_formats/pandas/query_compiler.py

@@ -3157,9 +3157,7 @@ def dropna(self, **kwargs):
             lib.no_default,
             None,
         )
-        # FIXME: this is a naive workaround for this problem: https://github.com/modin-project/modin/issues/5394
-        # if there are too many partitions then all non-full-axis implementations start acting very badly.
-        # The here threshold is pretty random though it works fine on simple scenarios
+        # The map reduce approach works well for frames with few columnar partitions
         processable_amount_of_partitions = (
             self._modin_frame.num_parts < CpuCount.get() * 32
         )

modin/tests/pandas/test_groupby.py

@@ -21,7 +21,13 @@
 import pytest
 
 import modin.pandas as pd
-from modin.config import IsRayCluster, NPartitions, RangePartitioning, StorageFormat
+from modin.config import (
+    IsRayCluster,
+    NPartitions,
+    RangePartitioning,
+    StorageFormat,
+    context,
+)
 from modin.core.dataframe.algebra.default2pandas.groupby import GroupBy
 from modin.core.dataframe.pandas.partitioning.axis_partition import (
     PandasDataframeAxisPartition,
@@ -2431,6 +2437,31 @@ def test_multi_column_groupby_different_partitions(
     )
 
 
+def test_empty_partitions_after_groupby():
+    def func_to_apply(grp):
+        return grp.agg(
+            {
+                list(test_data_values[0].keys())[1]: "sum",
+                list(test_data_values[0].keys())[-1]: "sum",
+            }
+        )
+
+    data = test_data_values[0]
+    md_df, pd_df = create_test_dfs(data)
+    by = pd_df.columns[0]
+
+    with context(DynamicPartitioning=True):
+        md_grp, pd_grp = (
+            md_df.groupby(by),
+            pd_df.groupby(by),
+        )
+        eval_general(
+            md_grp,
+            pd_grp,
+            func_to_apply,
+        )
+
+
 @pytest.mark.parametrize(
     "by",
     [