Optimize monitor deletion to prevent n+1 queries

src/sentry/deletions/defaults/monitor.py

@@ -1,3 +1,7 @@
+from collections.abc import Sequence
+
+from sentry import quotas
+from sentry.constants import DataCategory
 from sentry.deletions.base import (
     BaseRelation,
     BulkModelDeletionTask,
@@ -17,3 +21,8 @@ def get_child_relations(self, instance: Monitor) -> list[BaseRelation]:
             ),
             ModelRelation(models.MonitorEnvironment, {"monitor_id": instance.id}),
         ]
+
+    def delete_instance_bulk(self, instance_list: Sequence[Monitor]) -> None:
+        if instance_list:
+            quotas.backend.remove_seats(DataCategory.MONITOR_SEAT, instance_list)
+        super().delete_instance_bulk(instance_list)

src/sentry/quotas/base.py

@@ -648,6 +648,18 @@ def remove_seat(self, data_category: DataCategory, seat_object: SeatObject) -> N
         Removes an assigned seat.
         """
 
+    def remove_seats(self, data_category: DataCategory, seat_objects: Sequence[SeatObject]) -> None:
+        """
+        Removes assigned seats for a batch of objects.
+
+        The default implementation simply iterates over ``seat_objects`` and calls
+        ``remove_seat`` for each item. Backends that need to perform additional bookkeeping
+        (for example, reducing database queries) can override this method to implement a more
+        efficient bulk removal.
+        """
+        for seat_object in seat_objects:
+            self.remove_seat(data_category, seat_object)
+
     def check_accept_monitor_checkin(self, project_id: int, monitor_slug: str):
         """
         Will return a `PermitCheckInStatus`.

tests/sentry/deletions/test_monitor.py

@@ -1,3 +1,6 @@
+from unittest import mock
+
+from sentry.constants import DataCategory
 from sentry.deletions.tasks.scheduled import run_scheduled_deletions
 from sentry.models.environment import Environment
 from sentry.models.project import Project
@@ -46,3 +49,22 @@ def test_simple(self) -> None:
         # Shared objects should continue to exist.
         assert Environment.objects.filter(id=env.id).exists()
         assert Project.objects.filter(id=project.id).exists()
+
+    @mock.patch("sentry.deletions.defaults.monitor.quotas.backend.remove_seats")
+    def test_removes_monitor_seats_before_delete(self, mock_remove_seats: mock.MagicMock) -> None:
+        project = self.create_project(name="with-seats")
+        monitor = Monitor.objects.create(
+            organization_id=project.organization.id,
+            project_id=project.id,
+            config={"schedule": "* * * * *", "schedule_type": ScheduleType.CRONTAB},
+        )
+
+        self.ScheduledDeletion.schedule(instance=monitor, days=0)
+
+        with self.tasks():
+            run_scheduled_deletions()
+
+        mock_remove_seats.assert_called_once()
+        args, _ = mock_remove_seats.call_args
+        assert args[0] == DataCategory.MONITOR_SEAT
+        assert list(args[1]) == [monitor]