chore(detectors): Fully replace N+1 Detectors with updated versions

[jasonyuezhang]

this pr fully replaces the legacy N+1 detectors (DB,MN+1 DB, API) with the updated versions (which are currently 100% released). replaces the legacy code with the updated code and deletes the experiment files.

---

Copied from getsentry#104199
Original PR: getsentry#104199

[propel-test-bot]

[PerformanceOptimization]

O(N*M) complexity issue with parent span lookup: The _find_common_parent_span() method iterates through all spans in the event for each call (line 346-349). If there are 1000+ spans in the event, this becomes expensive. Consider building a span_id -> span lookup map once in __init__:

def __init__(self, ...):
    self.span_lookup = {span.get("span_id"): span for span in event.get("spans", [])}

# Then in _find_common_parent_span:
return self.span_lookup.get(common_parent_span_id)

Context for Agents

**O(N*M) complexity issue with parent span lookup**: The `_find_common_parent_span()` method iterates through all spans in the event for each call (line 346-349). If there are 1000+ spans in the event, this becomes expensive. Consider building a span_id -> span lookup map once in `__init__`:

```python
def __init__(self, ...):
    self.span_lookup = {span.get("span_id"): span for span in event.get("spans", [])}

# Then in _find_common_parent_span:
return self.span_lookup.get(common_parent_span_id)
```

File: src/sentry/issue_detection/detectors/mn_plus_one_db_span_detector.py
Line: 349

[propel-test-bot]

[BestPractice]

Potential infinite loop with deque maxlen: The recent_spans deque has maxlen=self.settings["max_sequence_length"] (line 75). If max_sequence_length is set to 0 or negative, operations on this deque could behave unexpectedly. Add validation:

max_length = self.settings["max_sequence_length"]
if max_length <= 0:
    raise ValueError(f"max_sequence_length must be positive, got {max_length}")
self.recent_spans = deque(initial_spans or [], max_length)

Context for Agents

**Potential infinite loop with deque maxlen**: The `recent_spans` deque has `maxlen=self.settings["max_sequence_length"]` (line 75). If `max_sequence_length` is set to 0 or negative, operations on this deque could behave unexpectedly. Add validation:

```python
max_length = self.settings["max_sequence_length"]
if max_length <= 0:
    raise ValueError(f"max_sequence_length must be positive, got {max_length}")
self.recent_spans = deque(initial_spans or [], max_length)
```

File: src/sentry/issue_detection/detectors/mn_plus_one_db_span_detector.py
Line: 75

[propel-test-bot]

[CriticalError]

Missing Error Handling: If urlparse() throws a ValueError for malformed URLs, the entire detector will crash and fail to process the event. While the old code had try-catch with logging (removed in this change), the new code at line 139 directly calls urlparse() without protection:

parsed_url = urlparse(str(url))  # Can throw ValueError

Specific scenario: URLs with null bytes, invalid schemes, or extremely long URLs can cause urlparse() to fail.

Fix: Re-add error handling:

try:
    parsed_url = urlparse(str(url))
except (ValueError, TypeError) as e:
    logging.exception(
        "N+1 API Calls Detector: URL parsing failed",
        extra={"url": url, "error": str(e)}
    )
    return False

Context for Agents

**Missing Error Handling**: If `urlparse()` throws a `ValueError` for malformed URLs, the entire detector will crash and fail to process the event. While the old code had try-catch with logging (removed in this change), the new code at line 139 directly calls `urlparse()` without protection:

```python
parsed_url = urlparse(str(url))  # Can throw ValueError
```

**Specific scenario**: URLs with null bytes, invalid schemes, or extremely long URLs can cause `urlparse()` to fail.

**Fix**: Re-add error handling:
```python
try:
    parsed_url = urlparse(str(url))
except (ValueError, TypeError) as e:
    logging.exception(
        "N+1 API Calls Detector: URL parsing failed",
        extra={"url": url, "error": str(e)}
    )
    return False
```

File: src/sentry/issue_detection/detectors/n_plus_one_api_calls_detector.py
Line: 139

[propel-test-bot]

[PerformanceOptimization]

N+1 Query Pattern: This code has an N+1 query vulnerability in _find_common_parent_span(). For each offender span (N), the method iterates up to max_allowable_depth levels through self.parent_map, then searches through all spans in the event:

for span in spans:  # N offender spans
    for _ in range(self.settings["max_allowable_depth"]):  # Up to 3 levels
        parent_span_id = self.parent_map.get(current_span_id)
        # ...
    # Then searches all_spans again
    all_spans = self.event.get("spans") or []
    for span in all_spans:  # M spans in event
        if span.get("span_id") == common_parent_span_id:
            return span

With 100 offender spans and 1000 event spans, this becomes ~100k iterations.

Fix: Build a span lookup dictionary once:

def __init__(self, ...):
    # ...
    self.span_lookup = {s.get("span_id"): s for s in self.event.get("spans", [])}

# Then in _find_common_parent_span:
return self.span_lookup.get(common_parent_span_id)

Context for Agents

**N+1 Query Pattern**: This code has an N+1 query vulnerability in `_find_common_parent_span()`. For each offender span (N), the method iterates up to `max_allowable_depth` levels through `self.parent_map`, then searches through all spans in the event:

```python
for span in spans:  # N offender spans
    for _ in range(self.settings["max_allowable_depth"]):  # Up to 3 levels
        parent_span_id = self.parent_map.get(current_span_id)
        # ...
    # Then searches all_spans again
    all_spans = self.event.get("spans") or []
    for span in all_spans:  # M spans in event
        if span.get("span_id") == common_parent_span_id:
            return span
```

With 100 offender spans and 1000 event spans, this becomes ~100k iterations.

**Fix**: Build a span lookup dictionary once:
```python
def __init__(self, ...):
    # ...
    self.span_lookup = {s.get("span_id"): s for s in self.event.get("spans", [])}

# Then in _find_common_parent_span:
return self.span_lookup.get(common_parent_span_id)
```

File: src/sentry/issue_detection/detectors/mn_plus_one_db_span_detector.py
Line: 350