Calculating the billing units per month was taking too long for a services with a lot of data.

The query now does the sum per month.

app/dao/notifications_dao.py

@@ -1,14 +1,13 @@
+
 import pytz
 from datetime import (
     datetime,
     timedelta,
-    date
+    date)
-)
-from itertools import groupby
 
 from flask import current_app
 from werkzeug.datastructures import MultiDict
-from sqlalchemy import (desc, func, or_, and_, asc)
+from sqlalchemy import (desc, func, or_, and_, asc, extract)
 from sqlalchemy.orm import joinedload
 
 from app import db, create_uuid
@@ -217,23 +216,16 @@ def get_notification_billable_unit_count_per_month(service_id, year):
     start, end = get_financial_year(year)
 
     notifications = db.session.query(
-        NotificationHistory.created_at,
+        func.date_trunc("month", (NotificationHistory.created_at + extract("timezone", func.timezone("Europe/London", NotificationHistory.created_at)) * timedelta(seconds=1))),
-        NotificationHistory.billable_units
+        func.sum(NotificationHistory.billable_units)
-    ).order_by(
-        NotificationHistory.created_at
     ).filter(
         NotificationHistory.billable_units != 0,
         NotificationHistory.service_id == service_id,
         NotificationHistory.created_at >= start,
         NotificationHistory.created_at < end
-    )
+    ).group_by(func.date_trunc("month", (NotificationHistory.created_at + extract("timezone", func.timezone("Europe/London", NotificationHistory.created_at)) * timedelta(seconds=1)))).all()
 
-    return [
+    return [(datetime.strftime(x[0], "%B"), x[1]) for x in notifications]
-        (month, sum(count for _, count in row))
-        for month, row in groupby(
-            notifications, lambda row: get_bst_month(row[0])
-        )
-    ]
 
 
 @statsd(namespace="dao")

tests/app/dao/test_notification_dao.py

@@ -700,21 +700,23 @@ def test_get_all_notifications_for_job_by_status(notify_db, notify_db_session, s
 
 def test_get_notification_billable_unit_count_per_month(notify_db, notify_db_session, sample_service):
 
-    for year, month, day in (
+    for year, month, day, hour, minute, second in (
-        (2017, 1, 15),  # ↓ 2016 financial year
+        (2017, 1, 15, 23, 59, 59),  # ↓ 2016 financial year
-        (2016, 8, 1),
+        (2016, 9, 30, 23, 59, 59),  # counts in October (BST conversion)
-        (2016, 7, 15),
+        (2016, 6, 30, 23, 50, 20),
-        (2016, 4, 15),
+        (2016, 7, 15, 9, 20, 25),
-        (2016, 4, 15),
+        (2016, 4, 15, 12, 30, 00),
-        (2016, 4, 1),  # ↓ 2015 financial year
+        (2016, 4, 1, 1, 1, 00),
-        (2016, 3, 31),
+        (2016, 4, 1, 0, 0, 00),  # ↓ 2015 financial year
-        (2016, 1, 15)
+        (2016, 3, 20, 22, 40, 45),
+        (2015, 11, 20, 22, 40, 45),
+        (2016, 1, 15, 2, 30, 40)
     ):
         sample_notification(
             notify_db, notify_db_session, service=sample_service,
             created_at=datetime(
-                year, month, day, 0, 0, 0, 0
+                year, month, day, hour, minute, second, 0
-            ) - timedelta(hours=1, seconds=1)  # one second before midnight
+            )
         )
 
     for financial_year, months in (
@@ -724,11 +726,11 @@ def test_get_notification_billable_unit_count_per_month(notify_db, notify_db_ses
         ),
         (
             2016,
-            [('April', 2), ('July', 2), ('January', 1)]
+            [('April', 2), ('July', 2), ('October', 1), ('January', 1)]
         ),
         (
             2015,
-            [('January', 1), ('March', 2)]
+            [('November', 1), ('January', 1), ('March', 1), ('April', 1)]
         ),
         (
             2014,