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Oct 29, 2025
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fix(django): Improve logic for classifying cache hits and misses #5029

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fix(django): Improve logic for classifying cache hits or misses
alexander-alderman-webb Oct 24, 2025
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alexander-alderman-webb Oct 28, 2025
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fix existing tests
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19 changes: 16 additions & 3 deletions sentry_sdk/integrations/django/caching.py
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Original file line number Diff line number Diff line change
Expand Up @@ -45,7 +45,8 @@ def _instrument_call(
):
# type: (CacheHandler, str, Callable[..., Any], tuple[Any, ...], dict[str, Any], Optional[str], Optional[int]) -> Any
is_set_operation = method_name.startswith("set")
is_get_operation = not is_set_operation
is_get_method = method_name == "get"
is_get_many_method = method_name == "get_many"

op = OP.CACHE_PUT if is_set_operation else OP.CACHE_GET
description = _get_span_description(method_name, args, kwargs)
Expand All @@ -69,8 +70,20 @@ def _instrument_call(
span.set_data(SPANDATA.CACHE_KEY, key)

item_size = None
if is_get_operation:
if value:
if is_get_many_method:
if value != {}:
item_size = len(str(value))
span.set_data(SPANDATA.CACHE_HIT, True)
else:
span.set_data(SPANDATA.CACHE_HIT, False)
elif is_get_method:
default_value = None
if len(args) >= 2:
default_value = args[1]
elif "default" in kwargs:
default_value = kwargs["default"]

if value != default_value:
item_size = len(str(value))
span.set_data(SPANDATA.CACHE_HIT, True)
else:
Expand Down
76 changes: 72 additions & 4 deletions tests/integrations/django/test_cache_module.py
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Original file line number Diff line number Diff line change
Expand Up @@ -223,8 +223,8 @@ def test_cache_spans_middleware(
assert second_event["spans"][0]["data"]["cache.key"][0].startswith(
"views.decorators.cache.cache_header."
)
assert not second_event["spans"][0]["data"]["cache.hit"]
assert "cache.item_size" not in second_event["spans"][0]["data"]
assert second_event["spans"][0]["data"]["cache.hit"]
assert second_event["spans"][0]["data"]["cache.item_size"] == 2
Comment on lines -226 to +227
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@alexander-alderman-webb alexander-alderman-webb Oct 28, 2025 •
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Previously marked as a cache miss because [] is falsy.

I do not understand the intent behind asserting a cache miss here, because we assert information about the corresponding cache.put further up in the test.

sentry-python/tests/integrations/django/test_cache_module.py

Lines 206 to 216 in 64c145f

# first_event - cache.put
assert first_event["spans"][1]["op"] == "cache.put"
assert first_event["spans"][1]["description"].startswith(
"views.decorators.cache.cache_header."
)
assert first_event["spans"][1]["data"]["network.peer.address"] is not None
assert first_event["spans"][1]["data"]["cache.key"][0].startswith(
"views.decorators.cache.cache_header."
)
assert "cache.hit" not in first_event["spans"][1]["data"]
assert first_event["spans"][1]["data"]["cache.item_size"] == 2

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This test confuses me too. It calls the not_cached_view view, which, unlike the cached_view, doesn't have the @cache_page decorator. Is there some automatic caching going on anyway even without the decorator? Is some caching always happening because of our use of the use_django_caching_with_middlewares fixture in this test? It definitely seems like it since we're getting cache spans.

The cache miss asserts look wrong to me too. It should be a cache hit. But I don't understand why cache.item_size is now different?

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Yes, the caching only occurs because of the use_django_caching_with_middlewares() fixture here. Without the fixture no spans are generated.

The item's size is 2 because len(str([])) == 2, while previously we did not store the item size at all because we were in the else branch below due to [] being falsy:

sentry-python/sentry_sdk/integrations/django/caching.py

Lines 73 to 77 in 64c145f

if value:
item_size = len(str(value))
span.set_data(SPANDATA.CACHE_HIT, True)
else:
span.set_data(SPANDATA.CACHE_HIT, False)

The empty list value originates from

https://github.com/django/django/blob/9ba3f74a46d15f9f2f45ad4ef8cdd245a888e58e/django/utils/cache.py#L437

# second_event - cache.get 2
assert second_event["spans"][1]["op"] == "cache.get"
assert second_event["spans"][1]["description"].startswith(
Expand Down Expand Up @@ -501,14 +501,76 @@ def test_cache_spans_item_size(sentry_init, client, capture_events, use_django_c

assert len(second_event["spans"]) == 2
assert second_event["spans"][0]["op"] == "cache.get"
assert not second_event["spans"][0]["data"]["cache.hit"]
assert "cache.item_size" not in second_event["spans"][0]["data"]
assert second_event["spans"][0]["data"]["cache.hit"]
assert second_event["spans"][0]["data"]["cache.item_size"] == 2
Comment on lines -504 to +505
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@alexander-alderman-webb alexander-alderman-webb Oct 28, 2025 •
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Previously marked as a cache miss because [] is falsy.

Similar reasoning to the other assertion I changed.


assert second_event["spans"][1]["op"] == "cache.get"
assert second_event["spans"][1]["data"]["cache.hit"]
assert second_event["spans"][1]["data"]["cache.item_size"] == 58


@pytest.mark.forked
@pytest_mark_django_db_decorator()
def test_cache_spans_get_custom_default(
sentry_init, capture_events, use_django_caching
):
sentry_init(
integrations=[
DjangoIntegration(
cache_spans=True,
middleware_spans=False,
signals_spans=False,
)
],
traces_sample_rate=1.0,
)
events = capture_events()

id = os.getpid()

from django.core.cache import cache

with sentry_sdk.start_transaction():
cache.set(f"S{id}", "Sensitive1")
cache.set(f"S{id + 1}", "")

cache.get(f"S{id}", "null")
cache.get(f"S{id}", default="null")

cache.get(f"S{id + 1}", "null")
cache.get(f"S{id + 1}", default="null")

cache.get(f"S{id + 2}", "null")
cache.get(f"S{id + 2}", default="null")

(transaction,) = events
assert len(transaction["spans"]) == 8

assert transaction["spans"][0]["op"] == "cache.put"
assert transaction["spans"][0]["description"] == f"S{id}"

assert transaction["spans"][1]["op"] == "cache.put"
assert transaction["spans"][1]["description"] == f"S{id + 1}"

for span in (transaction["spans"][2], transaction["spans"][3]):
assert span["op"] == "cache.get"
assert span["description"] == f"S{id}"
assert span["data"]["cache.hit"]
assert span["data"]["cache.item_size"] == 10

for span in (transaction["spans"][4], transaction["spans"][5]):
assert span["op"] == "cache.get"
assert span["description"] == f"S{id + 1}"
assert span["data"]["cache.hit"]
assert span["data"]["cache.item_size"] == 0

for span in (transaction["spans"][6], transaction["spans"][7]):
assert span["op"] == "cache.get"
assert span["description"] == f"S{id + 2}"
assert not span["data"]["cache.hit"]
assert "cache.item_size" not in span["data"]


@pytest.mark.forked
@pytest_mark_django_db_decorator()
def test_cache_spans_get_many(sentry_init, capture_events, use_django_caching):
Expand Down Expand Up @@ -538,24 +600,30 @@ def test_cache_spans_get_many(sentry_init, capture_events, use_django_caching):

assert transaction["spans"][0]["op"] == "cache.get"
assert transaction["spans"][0]["description"] == f"S{id}, S{id + 1}"
assert not transaction["spans"][0]["data"]["cache.hit"]

assert transaction["spans"][1]["op"] == "cache.get"
assert transaction["spans"][1]["description"] == f"S{id}"
assert not transaction["spans"][1]["data"]["cache.hit"]

assert transaction["spans"][2]["op"] == "cache.get"
assert transaction["spans"][2]["description"] == f"S{id + 1}"
assert not transaction["spans"][2]["data"]["cache.hit"]

assert transaction["spans"][3]["op"] == "cache.put"
assert transaction["spans"][3]["description"] == f"S{id}"

assert transaction["spans"][4]["op"] == "cache.get"
assert transaction["spans"][4]["description"] == f"S{id}, S{id + 1}"
assert transaction["spans"][4]["data"]["cache.hit"]

assert transaction["spans"][5]["op"] == "cache.get"
assert transaction["spans"][5]["description"] == f"S{id}"
assert transaction["spans"][5]["data"]["cache.hit"]

assert transaction["spans"][6]["op"] == "cache.get"
assert transaction["spans"][6]["description"] == f"S{id + 1}"
assert not transaction["spans"][6]["data"]["cache.hit"]


@pytest.mark.forked
Expand Down