fix(am1): Add span count metric (unrevert) (#75827)

We ran into trouble with the previous PR due to a few issues; a typo in
the name, exception logging in the 'has' causing a thundering herd of
exceptions, and the condition order causing the problem to not trip
tests / soak time.

original PR for context: #75485

Notes:
- `am3_tier` vs `am3-tier` as a result of a bad copy paste (out of a
thread instead of the file it's registered)
- `logger.exception` circumventing the `try / except`, already fixed
[here](687086f#diff-9cd8ed7a349a276392e908cabcd613d3647a94eaa5956ae79e4efb604e2c9232L309)
- Conditional order has `organizations:dynamic-sampling` first, which
causes an early shortcut of the `and`

src/sentry/ingest/consumer/processors.py

@@ -1,6 +1,6 @@
 import functools
 import logging
-from collections.abc import Mapping
+from collections.abc import Mapping, MutableMapping
 from typing import Any
 
 import orjson
@@ -187,6 +187,11 @@ def process_event(
                 event_id=event_id,
                 project_id=project_id,
             )
+
+            try:
+                collect_span_metrics(project, data)
+            except Exception:
+                pass
         elif data.get("type") == "feedback":
             if features.has("organizations:user-feedback-ingest", project.organization, actor=None):
                 save_event_feedback.delay(
@@ -324,3 +329,20 @@ def process_userreport(message: IngestMessage, project: Project) -> bool:
         # If you want to remove this make sure to have triaged all errors in Sentry
         logger.exception("userreport.save.crash")
         return False
+
+
+def collect_span_metrics(
+    project: Project,
+    data: MutableMapping[str, Any],
+):
+    if not features.has("organizations:am3-tier", project.organization) and not features.has(
+        "organizations:dynamic-sampling", project.organization
+    ):
+        amount = (
+            len(data.get("spans", [])) + 1
+        )  # Segment spans also get added to the total span count.
+        metrics.incr(
+            "event.save_event.unsampled.spans.count",
+            amount=amount,
+            tags={"organization": project.organization.slug},
+        )

tests/sentry/ingest/ingest_consumer/test_ingest_consumer_processing.py

@@ -6,7 +6,7 @@
 import zipfile
 from io import BytesIO
 from typing import Any
-from unittest.mock import Mock
+from unittest.mock import Mock, patch
 
 import orjson
 import pytest
@@ -19,6 +19,7 @@
 from sentry import eventstore
 from sentry.event_manager import EventManager
 from sentry.ingest.consumer.processors import (
+    collect_span_metrics,
     process_attachment_chunk,
     process_event,
     process_individual_attachment,
@@ -28,6 +29,7 @@
 from sentry.models.eventattachment import EventAttachment
 from sentry.models.userreport import UserReport
 from sentry.options import set
+from sentry.testutils.helpers.features import Feature
 from sentry.testutils.pytest.fixtures import django_db_all
 from sentry.testutils.skips import requires_snuba, requires_symbolicator
 from sentry.usage_accountant import accountant
@@ -595,3 +597,19 @@ def test_individual_attachments_missing_chunks(default_project, factories, monke
     attachments = list(EventAttachment.objects.filter(project_id=project_id, event_id=event_id))
 
     assert not attachments
+
+
+@django_db_all
+def test_collect_span_metrics(default_project):
+    with Feature({"organizations:dynamic-sampling": True, "organization:am3-tier": True}):
+        with patch("sentry.ingest.consumer.processors.metrics") as mock_metrics:
+            assert mock_metrics.incr.call_count == 0
+            collect_span_metrics(default_project, {"spans": [1, 2, 3]})
+            assert mock_metrics.incr.call_count == 0
+
+    with Feature({"organizations:dynamic-sampling": False, "organization:am3-tier": False}):
+        with patch("sentry.ingest.consumer.processors.metrics") as mock_metrics:
+
+            assert mock_metrics.incr.call_count == 0
+            collect_span_metrics(default_project, {"spans": [1, 2, 3]})
+            assert mock_metrics.incr.call_count == 1