Update FactStatus table in bulk for each service

Previously we were looping over data from the Notifications/History
table and then shovelling it into the status table, one row at a time
- plus an extra delete to clean up any existing data.

This replaces that with a batch insertion, similar to how we archive
notifications [1], but using a simple subquery (via "from_select" [2])
instead of a temporary table.

To make the select compatible with the insert, I've used "literal"
to inject the constant pieces of data, so each row has everything it
needs to go into the status table.

[1]: 9ce6d2fe92/app/dao/notifications_dao.py (L295)
[2]: https://docs.sqlalchemy.org/en/14/core/dml.html#sqlalchemy.sql.expression.Insert.from_select

app/dao/fact_notification_status_dao.py

@@ -34,59 +34,66 @@ from app.utils import (
 )
 
 
-def fetch_status_data_for_service_and_day(process_day, service_id, notification_type):
+@autocommit
+def update_fact_notification_status(process_day, notification_type, service_id):
     start_date = get_london_midnight_in_utc(process_day)
     end_date = get_london_midnight_in_utc(process_day + timedelta(days=1))
 
     # query notifications or notification_history for the day, depending on their data retention
     service = Service.query.get(service_id)
-    table = get_notification_table_to_use(service, notification_type, process_day, has_delete_task_run=False)
+    source_table = get_notification_table_to_use(
+        service,
+        notification_type,
+        process_day,
+        has_delete_task_run=False
+    )
 
-    return db.session.query(
-        table.template_id,
-        func.coalesce(table.job_id, '00000000-0000-0000-0000-000000000000').label('job_id'),
-        table.key_type,
-        table.status,
+    query = db.session.query(
+        literal(process_day).label("process_day"),
+        source_table.template_id,
+        literal(service_id).label("service_id"),
+        func.coalesce(source_table.job_id, '00000000-0000-0000-0000-000000000000').label('job_id'),
+        literal(notification_type).label("notification_type"),
+        source_table.key_type,
+        source_table.status,
         func.count().label('notification_count')
     ).filter(
-        table.created_at >= start_date,
-        table.created_at < end_date,
-        table.notification_type == notification_type,
-        table.service_id == service_id,
-        table.key_type.in_((KEY_TYPE_NORMAL, KEY_TYPE_TEAM)),
+        source_table.created_at >= start_date,
+        source_table.created_at < end_date,
+        source_table.notification_type == notification_type,
+        source_table.service_id == service_id,
+        source_table.key_type.in_((KEY_TYPE_NORMAL, KEY_TYPE_TEAM)),
     ).group_by(
-        table.template_id,
+        source_table.template_id,
+        source_table.template_id,
         'job_id',
-        table.key_type,
-        table.status
-    ).all()
+        source_table.key_type,
+        source_table.status
+    )
 
+    stmt = insert(FactNotificationStatus.__table__).from_select(
+        [
+            FactNotificationStatus.bst_date,
+            FactNotificationStatus.template_id,
+            FactNotificationStatus.service_id,
+            FactNotificationStatus.job_id,
+            FactNotificationStatus.notification_type,
+            FactNotificationStatus.key_type,
+            FactNotificationStatus.notification_status,
+            FactNotificationStatus.notification_count
+        ],
+        query
+    )
 
-@autocommit
-def update_fact_notification_status(new_status_rows, process_day, notification_type, service_id):
-    table = FactNotificationStatus.__table__
+    stmt = stmt.on_conflict_do_update(
+        constraint="ft_notification_status_pkey",
+        set_={
+            FactNotificationStatus.notification_count: stmt.excluded.notification_count,
+            FactNotificationStatus.updated_at: datetime.utcnow()
+        }
+    )
 
-    for row in new_status_rows:
-        stmt = insert(table).values(
-            bst_date=process_day,
-            template_id=row.template_id,
-            service_id=service_id,
-            job_id=row.job_id,
-            notification_type=notification_type,
-            key_type=row.key_type,
-            notification_status=row.status,
-            notification_count=row.notification_count,
-        )
-
-        stmt = stmt.on_conflict_do_update(
-            constraint="ft_notification_status_pkey",
-            set_={
-                FactNotificationStatus.notification_count: stmt.excluded.notification_count,
-                FactNotificationStatus.updated_at: datetime.utcnow()
-            }
-        )
-
-        db.session.connection().execute(stmt)
+    db.session.connection().execute(stmt)
 
 
 def fetch_notification_status_for_service_by_month(start_date, end_date, service_id):