UN-3973 [DEV] Cut dashboard cron DB time by deriving monthly metrics from the daily tier

backend/dashboard_metrics/migrations/0005_add_reconciliation_task.py

@@ -0,0 +1,61 @@
+"""Data migration to schedule the daily-tier reconciliation pass.
+
+The 15-minute aggregation reads a narrow source window, which cannot repair
+gaps left by cron downtime. This runs the same task once a day at a wider
+window to backfill them.
+"""
+
+from django.db import migrations
+
+RECONCILE_TASK_NAME = "dashboard_metrics_reconcile_source_window"
+
+
+def create_reconciliation_task(apps, schema_editor):
+    """Create the once-daily reconciliation periodic task."""
+    crontab_model = apps.get_model("django_celery_beat", "CrontabSchedule")
+    periodic_task_model = apps.get_model("django_celery_beat", "PeriodicTask")
+
+    # 4:00 AM UTC — clear of the 2:00 and 3:00 cleanup tasks
+    schedule_4am, _ = crontab_model.objects.get_or_create(
+        minute="0",
+        hour="4",
+        day_of_week="*",
+        day_of_month="*",
+        month_of_year="*",
+        defaults={"timezone": "UTC"},
+    )
+
+    periodic_task_model.objects.update_or_create(
+        name=RECONCILE_TASK_NAME,
+        defaults={
+            "task": "dashboard_metrics.aggregate_from_sources",
+            "crontab": schedule_4am,
+            "queue": "dashboard_metric_events",
+            "kwargs": '{"source_window_days": 7}',
+            "enabled": True,
+            "description": (
+                "Re-aggregate metrics over a 7 day source window to repair "
+                "daily-tier gaps left by cron downtime"
+            ),
+        },
+    )
+
+
+def remove_reconciliation_task(apps, schema_editor):
+    """Remove the reconciliation periodic task on rollback."""
+    periodic_task_model = apps.get_model("django_celery_beat", "PeriodicTask")
+    periodic_task_model.objects.filter(name=RECONCILE_TASK_NAME).delete()
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("dashboard_metrics", "0004_pg_periodic_tasks"),
+        ("django_celery_beat", "0018_improve_crontab_helptext"),
+    ]
+
+    operations = [
+        migrations.RunPython(
+            create_reconciliation_task,
+            remove_reconciliation_task,
+        ),
+    ]