__dask_tokenize__ (pydata#3446)

* Implement __dask_tokenize__

* Fix window test

* Code review

* Test change in IndexVariable

doc/whats-new.rst

@@ -21,17 +21,20 @@ v0.14.1 (unreleased)
 Breaking changes
 ~~~~~~~~~~~~~~~~
 
-- Minimum cftime version is now 1.0.3. By `Deepak Cherian <https://github.com/dcherian>`_.
+- Broken compatibility with cftime < 1.0.3.
+  By `Deepak Cherian <https://github.com/dcherian>`_.
 
   .. note::
 
-    cftime version 1.0.4 is broken (`cftime/126 <https://github.com/Unidata/cftime/issues/126>`_), use version 1.0.4.2 instead. 
+    cftime version 1.0.4 is broken
+    (`cftime/126 <https://github.com/Unidata/cftime/issues/126>`_);
+    please use version 1.0.4.2 instead.
 
 - All leftover support for dates from non-standard calendars through netcdftime, the
   module included in versions of netCDF4 prior to 1.4 that eventually became the
   cftime package, has been removed in favor of relying solely on the standalone
-  cftime package (:pull:`3450`).  By `Spencer Clark 
-  <https://github.com/spencerkclark>`_. 
+  cftime package (:pull:`3450`).
+  By `Spencer Clark <https://github.com/spencerkclark>`_.
 
 New Features
 ~~~~~~~~~~~~
@@ -52,6 +55,14 @@ New Features
   for now. Enable it with :py:meth:`xarray.set_options(display_style="html")`.
   (:pull:`3425`) by `Benoit Bovy <https://github.com/benbovy>`_ and
   `Julia Signell <https://github.com/jsignell>`_.
+- Implement `dask deterministic hashing
+  <https://docs.dask.org/en/latest/custom-collections.html#deterministic-hashing>`_
+  for xarray objects. Note that xarray objects with a dask.array backend already used
+  deterministic hashing in previous releases; this change implements it when whole
+  xarray objects are embedded in a dask graph, e.g. when :meth:`DataArray.map` is
+  invoked. (:issue:`3378`, :pull:`3446`)
+  By `Deepak Cherian <https://github.com/dcherian>`_ and
+  `Guido Imperiale <https://github.com/crusaderky>`_.
 
 Bug fixes
 ~~~~~~~~~
@@ -96,6 +107,7 @@ Internal Changes
 - Use Python 3.6 idioms throughout the codebase. (:pull:3419)
   By `Maximilian Roos <https://github.com/max-sixty>`_
 
+
 .. _whats-new.0.14.0:
 
 v0.14.0 (14 Oct 2019)

xarray/core/dataarray.py

@@ -752,6 +752,9 @@ def reset_coords(
             dataset[self.name] = self.variable
             return dataset
 
+    def __dask_tokenize__(self):
+        return (type(self), self._variable, self._coords, self._name)
+
     def __dask_graph__(self):
         return self._to_temp_dataset().__dask_graph__()
 

xarray/core/dataset.py

@@ -651,6 +651,9 @@ def load(self, **kwargs) -> "Dataset":
 
         return self
 
+    def __dask_tokenize__(self):
+        return (type(self), self._variables, self._coord_names, self._attrs)
+
     def __dask_graph__(self):
         graphs = {k: v.__dask_graph__() for k, v in self.variables.items()}
         graphs = {k: v for k, v in graphs.items() if v is not None}

xarray/core/variable.py

@@ -390,6 +390,11 @@ def compute(self, **kwargs):
         new = self.copy(deep=False)
         return new.load(**kwargs)
 
+    def __dask_tokenize__(self):
+        # Use v.data, instead of v._data, in order to cope with the wrappers
+        # around NetCDF and the like
+        return type(self), self._dims, self.data, self._attrs
+
     def __dask_graph__(self):
         if isinstance(self._data, dask_array_type):
             return self._data.__dask_graph__()
@@ -1963,6 +1968,10 @@ def __init__(self, dims, data, attrs=None, encoding=None, fastpath=False):
         if not isinstance(self._data, PandasIndexAdapter):
             self._data = PandasIndexAdapter(self._data)
 
+    def __dask_tokenize__(self):
+        # Don't waste time converting pd.Index to np.ndarray
+        return (type(self), self._dims, self._data.array, self._attrs)
+
     def load(self):
         # data is already loaded into memory for IndexVariable
         return self

xarray/tests/test_dask.py

@@ -1,5 +1,6 @@
 import operator
 import pickle
+import sys
 from contextlib import suppress
 from distutils.version import LooseVersion
 from textwrap import dedent
@@ -21,12 +22,16 @@
     assert_frame_equal,
     assert_identical,
     raises_regex,
+    requires_scipy_or_netCDF4,
 )
+from .test_backends import create_tmp_file
 
 dask = pytest.importorskip("dask")
 da = pytest.importorskip("dask.array")
 dd = pytest.importorskip("dask.dataframe")
 
+ON_WINDOWS = sys.platform == "win32"
+
 
 class CountingScheduler:
     """ Simple dask scheduler counting the number of computes.
@@ -1135,3 +1140,92 @@ def test_make_meta(map_ds):
     for variable in map_ds.data_vars:
         assert variable in meta.data_vars
         assert meta.data_vars[variable].shape == (0,) * meta.data_vars[variable].ndim
+
+
+@pytest.mark.parametrize(
+    "obj", [make_da(), make_da().compute(), make_ds(), make_ds().compute()]
+)
+@pytest.mark.parametrize(
+    "transform",
+    [
+        lambda x: x.reset_coords(),
+        lambda x: x.reset_coords(drop=True),
+        lambda x: x.isel(x=1),
+        lambda x: x.attrs.update(new_attrs=1),
+        lambda x: x.assign_coords(cxy=1),
+        lambda x: x.rename({"x": "xnew"}),
+        lambda x: x.rename({"cxy": "cxynew"}),
+    ],
+)
+def test_token_changes_on_transform(obj, transform):
+    with raise_if_dask_computes():
+        assert dask.base.tokenize(obj) != dask.base.tokenize(transform(obj))
+
+
+@pytest.mark.parametrize(
+    "obj", [make_da(), make_da().compute(), make_ds(), make_ds().compute()]
+)
+def test_token_changes_when_data_changes(obj):
+    with raise_if_dask_computes():
+        t1 = dask.base.tokenize(obj)
+
+    # Change data_var
+    if isinstance(obj, DataArray):
+        obj *= 2
+    else:
+        obj["a"] *= 2
+    with raise_if_dask_computes():
+        t2 = dask.base.tokenize(obj)
+    assert t2 != t1
+
+    # Change non-index coord
+    obj.coords["ndcoord"] *= 2
+    with raise_if_dask_computes():
+        t3 = dask.base.tokenize(obj)
+    assert t3 != t2
+
+    # Change IndexVariable
+    obj.coords["x"] *= 2
+    with raise_if_dask_computes():
+        t4 = dask.base.tokenize(obj)
+    assert t4 != t3
+
+
+@pytest.mark.parametrize("obj", [make_da().compute(), make_ds().compute()])
+def test_token_changes_when_buffer_changes(obj):
+    with raise_if_dask_computes():
+        t1 = dask.base.tokenize(obj)
+
+    if isinstance(obj, DataArray):
+        obj[0, 0] = 123
+    else:
+        obj["a"][0, 0] = 123
+    with raise_if_dask_computes():
+        t2 = dask.base.tokenize(obj)
+    assert t2 != t1
+
+    obj.coords["ndcoord"][0] = 123
+    with raise_if_dask_computes():
+        t3 = dask.base.tokenize(obj)
+    assert t3 != t2
+
+
+@pytest.mark.parametrize(
+    "transform",
+    [lambda x: x, lambda x: x.copy(deep=False), lambda x: x.copy(deep=True)],
+)
+@pytest.mark.parametrize("obj", [make_da(), make_ds(), make_ds().variables["a"]])
+def test_token_identical(obj, transform):
+    with raise_if_dask_computes():
+        assert dask.base.tokenize(obj) == dask.base.tokenize(transform(obj))
+    assert dask.base.tokenize(obj.compute()) == dask.base.tokenize(
+        transform(obj.compute())
+    )
+
+
+@requires_scipy_or_netCDF4
+def test_normalize_token_with_backend(map_ds):
+    with create_tmp_file(allow_cleanup_failure=ON_WINDOWS) as tmp_file:
+        map_ds.to_netcdf(tmp_file)
+        read = xr.open_dataset(tmp_file)
+        assert not dask.base.tokenize(map_ds) == dask.base.tokenize(read)

xarray/tests/test_sparse.py

@@ -11,7 +11,7 @@
 from xarray.core.npcompat import IS_NEP18_ACTIVE
 from xarray.core.pycompat import sparse_array_type
 
-from . import assert_equal, assert_identical
+from . import assert_equal, assert_identical, requires_dask
 
 param = pytest.param
 xfail = pytest.mark.xfail
@@ -849,3 +849,23 @@ def test_chunk():
     dsc = ds.chunk(2)
     assert dsc.chunks == {"dim_0": (2, 2)}
     assert_identical(dsc, ds)
+
+
+@requires_dask
+def test_dask_token():
+    import dask
+
+    s = sparse.COO.from_numpy(np.array([0, 0, 1, 2]))
+    a = DataArray(s)
+    t1 = dask.base.tokenize(a)
+    t2 = dask.base.tokenize(a)
+    t3 = dask.base.tokenize(a + 1)
+    assert t1 == t2
+    assert t3 != t2
+    assert isinstance(a.data, sparse.COO)
+
+    ac = a.chunk(2)
+    t4 = dask.base.tokenize(ac)
+    t5 = dask.base.tokenize(ac + 1)
+    assert t4 != t5
+    assert isinstance(ac.data._meta, sparse.COO)