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Cache JIT GroupBy.apply functions #12802

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merged 10 commits into from
Mar 24, 2023
Merged

Cache JIT GroupBy.apply functions #12802

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6e7af41
add caching to groupby jit
brandon-b-miller Feb 17, 2023
416589a
Merge branch 'branch-23.04' into groupby-apply-caching
brandon-b-miller Feb 22, 2023
d0ef1dc
add tests
brandon-b-miller Feb 23, 2023
e41b72c
Merge branch 'branch-23.04' into groupby-apply-caching
brandon-b-miller Mar 10, 2023
6866975
Update python/cudf/cudf/core/udf/groupby_utils.py
brandon-b-miller Mar 15, 2023
4858af2
Merge branch 'branch-23.04' into groupby-apply-caching
brandon-b-miller Mar 17, 2023
197bce6
Merge branch 'groupby-apply-caching' of github.com:brandon-b-miller/c…
brandon-b-miller Mar 17, 2023
425a912
denote groupby apply udfs in cache key
brandon-b-miller Mar 21, 2023
1fbc8f0
Merge branch 'branch-23.04' into groupby-apply-caching
brandon-b-miller Mar 22, 2023
136bc11
generate all of the cache key in _generate_cache_key
brandon-b-miller Mar 22, 2023
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14 changes: 10 additions & 4 deletions python/cudf/cudf/core/udf/groupby_utils.py
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Original file line number Diff line number Diff line change
Expand Up @@ -19,11 +19,13 @@
groupby_apply_kernel_template,
)
from cudf.core.udf.utils import (
_generate_cache_key,
_get_extensionty_size,
_get_kernel,
_get_udf_return_type,
_supported_cols_from_frame,
_supported_dtypes_from_frame,
precompiled,
)
from cudf.utils.utils import _cudf_nvtx_annotate

Expand Down Expand Up @@ -147,12 +149,16 @@ def jit_groupby_apply(offsets, grouped_values, function, *args):
offsets = cp.asarray(offsets)
ngroups = len(offsets) - 1

kernel, return_type = _get_groupby_apply_kernel(
grouped_values, function, args
)
return_type = numpy_support.as_dtype(return_type)
cache_key = _generate_cache_key(grouped_values, function)
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Is there a reason we don't use lru_cache and instead manually track cache keys? I assume it has to do with types being supported in lru_cache keys?

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In this context, precompiled is a cachetools.LRUCache. Are you asking why we don't do the following from functools?

@functools.lru_cache
def _get_groupby_apply_kernel(...)

If so the reason was that I wanted different UDF pipelines (apply, groupby.apply etc) to share the same cache.

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Nevermind. 😄 I didn't look closely enough at precompiled. But to clarify, how do you distinguish the type of UDF? Could an apply function and a groupby apply function reuse the same exact kernel? If not, how are the cache keys distinguished (for functions of the same data types)?

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@brandon-b-miller brandon-b-miller Mar 15, 2023 •
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The cache key is based on the bytecode of the UDF, the particulars are found here. I suppose you could get a cache hit erroneously if you:

  1. wrote a function f and executed it using DataFrame.apply
  2. applied the exact same f on a groupby result whose columns were the exact same dtypes as the dataframe that it was first applied to

However I would expect the above to cause a crash in pandas case as well since each API enforces a different syntax for the kinds of UDFs it accepts, so using one kind of function with the other's apply API probably wouldn't work in most cases.

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I'll defer to your judgment here -- but distinguishing keys clearly would be a plus, in my eyes. An erroneous cache hit would be bad.

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I added an extra tuple element to UDFs that go through GroupBy.apply that should break this degeneracy.

425a912

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Nice. Thanks!

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fwiw, I think I would have preferred an approach like _generate_cache_key(grouped_values, function, suffix="__GROUPBY_APPLY_UDF") where you provide a suffix to the function making the key. Not a dealbreaker but worth considering if we have more JIT code paths with separate JIT caches.

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I agree with you! The cache key should be generated within _generate_cache_key, not half in _generate_cache_key and half outside of the function. I updated this.

if cache_key not in precompiled:
precompiled[cache_key] = _get_groupby_apply_kernel(
grouped_values, function, args
)
kernel, return_type = precompiled[cache_key]

return_type = numpy_support.as_dtype(return_type)
output = cudf.core.column.column_empty(ngroups, dtype=return_type)

launch_args = [
offsets,
output,
Expand Down
37 changes: 37 additions & 0 deletions python/cudf/cudf/tests/test_groupby.py
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Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,7 @@
from cudf import DataFrame, Series
from cudf.core._compat import PANDAS_GE_150, PANDAS_LT_140
from cudf.core.udf.groupby_typing import SUPPORTED_GROUPBY_NUMPY_TYPES
from cudf.core.udf.utils import precompiled
from cudf.testing._utils import (
DATETIME_TYPES,
SIGNED_TYPES,
Expand Down Expand Up @@ -532,6 +533,42 @@ def diverging_block(grp_df):
run_groupby_apply_jit_test(df, diverging_block, ["a"])


def test_groupby_apply_caching():
# Make sure similar functions that differ
# by simple things like constants actually
# recompile

# begin with a clear cache
precompiled.clear()
assert precompiled.currsize == 0

data = cudf.DataFrame({"a": [1, 1, 1, 2, 2, 2], "b": [1, 2, 3, 4, 5, 6]})

def f(group):
return group["b"].mean() * 2

# a single run should result in a cache size of 1
run_groupby_apply_jit_test(data, f, ["a"])
assert precompiled.currsize == 1

# a second run with f should not increase the count
run_groupby_apply_jit_test(data, f, ["a"])
assert precompiled.currsize == 1

# changing a constant value inside the UDF should miss
def f(group):
return group["b"].mean() * 3

run_groupby_apply_jit_test(data, f, ["a"])
assert precompiled.currsize == 2

# changing the dtypes of the columns should miss
data["b"] = data["b"].astype("float64")
run_groupby_apply_jit_test(data, f, ["a"])

assert precompiled.currsize == 3


@pytest.mark.parametrize("nelem", [2, 3, 100, 500, 1000])
@pytest.mark.parametrize(
"func",
Expand Down