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fix: Send client reports for span recorder overflow #5310

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Merged
sentrivana merged 3 commits into from
Jan 14, 2026
+34 −5
Merged

fix: Send client reports for span recorder overflow #5310

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59a68d0
fix: Send client reports for span recorder overflow
sentrivana Jan 14, 2026
e853aa4
ref
sentrivana Jan 14, 2026
b501b8c
Merge branch 'master' into ivana/fix-client-reports-for-dropped-spans
sentrivana Jan 14, 2026
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19 changes: 14 additions & 5 deletions sentry_sdk/client.py
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Original file line number Diff line number Diff line change
Expand Up @@ -527,12 +527,21 @@ def _prepare_event(
spans_delta = spans_before - len(
cast(List[Dict[str, object]], event.get("spans", []))
)
if is_transaction and spans_delta > 0 and self.transport is not None:
self.transport.record_lost_event(
"event_processor", data_category="span", quantity=spans_delta
)
span_recorder_dropped_spans: int = event.pop("_dropped_spans", 0)

if is_transaction and self.transport is not None:
if spans_delta > 0:
self.transport.record_lost_event(
"event_processor", data_category="span", quantity=spans_delta
)
if span_recorder_dropped_spans > 0:
self.transport.record_lost_event(
"buffer_overflow",
data_category="span",
quantity=span_recorder_dropped_spans,
)
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@cursor cursor bot Jan 14, 2026

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Unfinished spans incorrectly reported as buffer overflow

Medium Severity

The _dropped_spans event field contains both spans dropped due to buffer overflow AND unfinished spans (those without a timestamp), but the new code reports all of them with reason "buffer_overflow". In tracing.py, _dropped_spans is calculated as len_diff + self._span_recorder.dropped_spans, where len_diff counts unfinished spans. Only self._span_recorder.dropped_spans represents actual buffer overflow. This causes unfinished spans to be incorrectly categorized in client reports.

Fix in Cursor Fix in Web


dropped_spans: int = event.pop("_dropped_spans", 0) + spans_delta
dropped_spans: int = span_recorder_dropped_spans + spans_delta
if dropped_spans > 0:
previous_total_spans = spans_before + dropped_spans
if scope._n_breadcrumbs_truncated > 0:
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20 changes: 20 additions & 0 deletions tests/tracing/test_misc.py
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Original file line number Diff line number Diff line change
Expand Up @@ -37,6 +37,26 @@ def test_span_trimming(sentry_init, capture_events):
assert "dropped_spans" not in event


def test_span_trimming_produces_client_report(
sentry_init, capture_events, capture_record_lost_event_calls
):
sentry_init(traces_sample_rate=1.0, _experiments={"max_spans": 3})
events = capture_events()
record_lost_event_calls = capture_record_lost_event_calls()

with start_transaction(name="hi"):
for i in range(10):
with start_span(op="foo{}".format(i)):
pass

(event,) = events

assert len(event["spans"]) == 3

# 7 spans were dropped (10 total - 3 kept = 7 dropped)
assert ("buffer_overflow", "span", None, 7) in record_lost_event_calls


def test_span_data_scrubbing_and_trimming(sentry_init, capture_events):
sentry_init(traces_sample_rate=1.0, _experiments={"max_spans": 3})
events = capture_events()
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