Add test

xarray/tests/test_dask.py

@@ -1746,3 +1746,20 @@ def test_new_index_var_computes_once():
     data = dask.array.from_array(np.array([100, 200]))
     with raise_if_dask_computes(max_computes=1):
         Dataset(coords={"z": ("z", data)})
+
+
+def test_minimize_graph_size():
+    import cloudpickle
+
+    # regression test for https://github.com/pydata/xarray/issues/8409
+    ds = Dataset(
+        {"foo": (("x", "y", "z"), dask.array.ones((120, 120, 120)))},
+        coords={"x": np.arange(120), "y": np.arange(120), "z": np.arange(120)},
+    ).chunk(x=20, y=20, z=1)
+
+    actual = len(cloudpickle.dumps(ds.map_blocks(lambda x: x)))
+    expected = len(cloudpickle.dumps(ds.drop_vars(ds.dims).map_blocks(lambda x: x)))
+
+    # prior to https://github.com/pydata/xarray/pull/8412
+    # actual is ~5x expected
+    assert actual < 2 * expected