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fix(detectors): Improve filtering for connection spans in N+1 DB detector #101217

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Oct 9, 2025
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fix(detectors): Improve filtering for connection spans in N+1 DB detector #101217

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11 changes: 10 additions & 1 deletion src/sentry/issue_detection/detectors/experiments/n_plus_one_db_span_detector.py
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Original file line number Diff line number Diff line change
Expand Up @@ -124,7 +124,11 @@ def on_complete(self) -> None:
self._maybe_store_problem()

def _is_db_op(self, op: str) -> bool:
return op.startswith("db") and not op.startswith("db.redis")
return (
op.startswith("db")
and not op.startswith("db.redis")
and not op.startswith("db.connection")
)

def _maybe_use_as_source(self, span: Span) -> None:
parent_span_id = span.get("parent_span_id", None)
Expand Down Expand Up @@ -279,6 +283,11 @@ def get_valid_db_span_description(span: Span) -> str | None:
"""
default_description = span.get("description", "")
db_system = span.get("sentry_tags", {}).get("system", "")

# Connection spans can have `op` as `db` but we don't want to trigger on them.
if "pg-pool.connect" in default_description:
return None
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Bug: N+1 Detector Span Processing Inconsistency

The N+1 detector inconsistently handles pg-pool.connect spans. They pass the initial _is_db_op() check, allowing partial processing, but are later filtered out by get_valid_db_span_description(). This can lead to false N+1 detections or problems failing to be stored.

Fix in Cursor Fix in Web

Comment on lines +288 to +289
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Potential bug: The code does not handle cases where a span's description is explicitly None, causing a TypeError when checking for a substring in a NoneType object.

  • Description: The code retrieves a span's description using span.get("description", ""). If a span contains an explicit {"description": None} entry, this method returns None rather than the default empty string. The subsequent line, if "pg-pool.connect" in default_description:, then attempts a substring check on this None value. This operation raises a TypeError because the in operator is not supported on NoneType objects. This unhandled exception will cause a crash in the performance issue detection pipeline whenever it processes a span with an explicit None description. Evidence from the codebase, including the Span.to_python() method and SpanBuilder type hints, confirms that a span's description can be None.

  • Suggested fix: Ensure the default_description variable is always a string by changing its assignment to default_description = span.get("description") or "". This safely handles cases where the description key is missing or its value is None, preventing the TypeError.
    severity: 0.7, confidence: 0.95

Did we get this right? 👍 / 👎 to inform future reviews.


# Trigger pathway on `mongodb`, `mongoose`, etc...
if "mongo" in db_system:
description = span.get("sentry_tags", {}).get("description")
Expand Down
30 changes: 29 additions & 1 deletion tests/sentry/issue_detection/experiments/test_n_plus_one_db_span_detector.py
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Original file line number Diff line number Diff line change
Expand Up @@ -18,7 +18,7 @@
from sentry.issues.issue_occurrence import IssueEvidence
from sentry.models.options.project_option import ProjectOption
from sentry.testutils.cases import TestCase
from sentry.testutils.issue_detection.event_generators import get_event
from sentry.testutils.issue_detection.event_generators import create_event, create_span, get_event


@pytest.mark.django_db
Expand Down Expand Up @@ -368,6 +368,34 @@ def test_detects_n_plus_one_with_mongoose(self) -> None:
assert len(problems) == 1
assert "mongoose" not in problems[0].desc

def test_does_not_detect_n_plus_one_with_pg_pool_connect(self) -> None:
source_span = create_span(
"db",
100,
"SELECT * FROM users WHERE id = 1",
hash="source_hash",
)

repeating_spans = [
create_span(
"db",
100,
"pg-pool.connect",
hash="pool_hash",
)
for _ in range(11)
]

event = create_event([source_span] + repeating_spans)
event["contexts"] = {
"trace": {
"span_id": "a" * 16,
"op": "http.server",
}
}

assert self.find_problems(event) == []


@pytest.mark.django_db
class NPlusOneDbSettingTest(TestCase):
Expand Down
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