FEAT-#7368: Add a new environment variable for using dynamic partitio…

…ning (#7369)

Signed-off-by: Kirill Suvorov <[email protected]>
Co-authored-by: Anatoly Myachev <[email protected]>

docs/usage_guide/optimization_notes/index.rst

@@ -37,6 +37,38 @@ Range-partitioning is not a silver bullet, meaning that enabling it is not alway
 a link to the list of operations that have support for range-partitioning and practical advices on when one should
 enable it: :doc:`operations that support range-partitioning </usage_guide/optimization_notes/range_partitioning_ops>`.
 
+Dynamic-partitioning in Modin
+"""""""""""""""""""""""""""""
+
+Ray engine experiences slowdowns when running a large number of small remote tasks at the same time. Ray Core recommends to `avoid tiny task`_.
+When modin DataFrame has a large number of partitions, some functions produce a large number of remote tasks, which can cause slowdowns. 
+To solve this problem, Modin suggests using dynamic partitioning. This approach reduces the number of remote tasks 
+by combining multiple partitions into a single virtual partition and perform a common remote task on them.
+
+Dynamic partitioning is typically used for operations that are fully or partially executed on all partitions separately.
+
+.. code-block:: python
+
+    import modin.pandas as pd
+    from modin.config import context
+
+    df = pd.DataFrame(...)
+
+    with context(DynamicPartitioning=True):
+        df.abs()
+
+Dynamic partitioning is also not always useful, and this approach is usually used for medium-sized DataFrames with a large number of columns.
+If the number of columns is small, the number of partitions will be close to the number of CPUs, and Ray will not have this problem.
+If the DataFrame has too many rows, this is also not a good case for using Dynamic-partitioning, since each task is no longer tiny and performing 
+the combined tasks carries more overhead than assigning them separately.
+
+Unfortunately, the use of Dynamic-partitioning depends on various factors such as data size, number of CPUs, operations performed, 
+and it is up to the user to determine whether Dynamic-partitioning will give a boost in his case or not.
+
+..
+  TODO: Define heuristics to automatically enable dynamic partitioning without performance penalty.
+  `Issue #7370 <https://github.com/modin-project/modin/issues/7370>`_
+
 Understanding Modin's partitioning mechanism
 """"""""""""""""""""""""""""""""""""""""""""
 
@@ -311,3 +343,4 @@ an inner join you may want to swap left and right DataFrames.
 Note that result columns order may differ for first and second ``merge``.
 
 .. _range-partitioning: https://www.techopedia.com/definition/31994/range-partitioning
+.. _`avoid tiny task`: https://docs.ray.io/en/latest/ray-core/tips-for-first-time.html#tip-2-avoid-tiny-tasks

modin/config/__init__.py

@@ -23,6 +23,7 @@
     CpuCount,
     DaskThreadsPerWorker,
     DocModule,
+    DynamicPartitioning,
     Engine,
     EnvironmentVariable,
     GithubCI,
@@ -95,6 +96,7 @@
     "AsyncReadMode",
     "ReadSqlEngine",
     "IsExperimental",
+    "DynamicPartitioning",
     # For tests
     "TrackFileLeaks",
     "TestReadFromSqlServer",

modin/config/envvars.py

@@ -892,6 +892,18 @@ class DaskThreadsPerWorker(EnvironmentVariable, type=int):
     default = 1
 
 
+class DynamicPartitioning(EnvironmentVariable, type=bool):
+    """
+    Set to true to use Modin's dynamic-partitioning implementation where possible.
+
+    Please refer to documentation for cases where enabling this options would be beneficial:
+    https://modin.readthedocs.io/en/stable/usage_guide/optimization_notes/index.html#dynamic-partitioning-in-modin
+    """
+
+    varname = "MODIN_DYNAMIC_PARTITIONING"
+    default = False
+
+
 def _check_vars() -> None:
     """
     Check validity of environment variables.

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

@@ -30,6 +30,7 @@
 from modin.config import (
     BenchmarkMode,
     CpuCount,
+    DynamicPartitioning,
     Engine,
     MinColumnPartitionSize,
     MinRowPartitionSize,
@@ -675,7 +676,7 @@ def map_partitions(
         NumPy array
             An array of partitions
         """
-        if np.prod(partitions.shape) <= 1.5 * CpuCount.get():
+        if not DynamicPartitioning.get():
             # block-wise map
             new_partitions = cls.base_map_partitions(
                 partitions, map_func, func_args, func_kwargs

modin/tests/core/storage_formats/pandas/test_internals.py

@@ -2658,7 +2658,7 @@ def remote_func():
         ),
     ],
 )
-def test_map_approaches(partitioning_scheme, expected_map_approach):
+def test_dynamic_partitioning(partitioning_scheme, expected_map_approach):
     data_size = MinRowPartitionSize.get() * CpuCount.get()
     data = {f"col{i}": np.ones(data_size) for i in range(data_size)}
     df = pandas.DataFrame(data)
@@ -2672,8 +2672,9 @@ def test_map_approaches(partitioning_scheme, expected_map_approach):
         expected_map_approach,
         wraps=getattr(partition_mgr_cls, expected_map_approach),
     ) as expected_method:
-        partition_mgr_cls.map_partitions(partitions, lambda x: x * 2)
-        expected_method.assert_called()
+        with context(DynamicPartitioning=True):
+            partition_mgr_cls.map_partitions(partitions, lambda x: x * 2)
+            expected_method.assert_called()
 
 
 def test_map_partitions_joined_by_column():