We had an exception today caused by a slow running query.

This PR will optimize this query to use a more efficient index.

- Add notification_type to the dao_get_last_template_usage to optimize the query.
- Tested and analyzed query on production database with very significant results.
 Before:
                                                                                 QUERY PLAN
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 Limit  (cost=0.43..1711.35 rows=1 width=935) (actual time=21186.053..21186.053 rows=0 loops=1)
   ->  Index Scan Backward using ix_notifications_created_at on notifications  (cost=0.43..4607493.80 rows=2693 width=935) (actual time=21186.052..21186.052 rows=0 loops=1)
         Filter: (((key_type)::text <> 'test'::text) AND (template_id = 'xxxxxx'::uuid))
         Rows Removed by Filter: 8244071
 Planning time: 0.112 ms
 Execution time: 21186.082 ms
 After:
                                                     QUERY PLAN
---------------------------------------------------------------------------------------------------------------------
 Limit  (cost=5323.10..5323.10 rows=1 width=935)
   ->  Sort  (cost=5323.10..5323.74 rows=258 width=935)
         Sort Key: created_at DESC
         ->  Index Scan using ix_notifications_template_id on notifications  (cost=0.56..5321.81 rows=258 width=935)
               Index Cond: (template_id = 'xxxxx'::uuid)
               Filter: (((key_type)::text <> 'test'::text) AND (notification_type = 'sms'::notification_type))
 Planning time: 1.102 ms
 Execution time: 0.584 ms

app/dao/notifications_dao.py

@@ -96,10 +96,11 @@ def dao_get_template_usage(service_id, limit_days=None):
 
 
 @statsd(namespace="dao")
-def dao_get_last_template_usage(template_id):
+def dao_get_last_template_usage(template_id, template_type):
     return Notification.query.filter(
         Notification.template_id == template_id,
-        Notification.key_type != KEY_TYPE_TEST
+        Notification.key_type != KEY_TYPE_TEST,
+        Notification.notification_type == template_type
     ).order_by(
         desc(Notification.created_at)
     ).first()

app/template_statistics/rest.py

@@ -63,7 +63,7 @@ def get_template_statistics_for_template_id(service_id, template_id):
         raise InvalidRequest(errors, status_code=404)
 
     data = None
-    notification = dao_get_last_template_usage(template_id)
+    notification = dao_get_last_template_usage(template_id, template.template_type)
     if notification:
         data = notification_with_template_schema.dump(notification).data
 

tests/app/dao/notification_dao/test_notification_dao.py

@@ -86,7 +86,7 @@ def test_should_be_able_to_get_template_usage_history(notify_db, notify_db_sessi
     with freeze_time('2000-01-01 12:00:00'):
         sms = create_sample_template(notify_db, notify_db_session)
         notification = sample_notification(notify_db, notify_db_session, service=sample_service, template=sms)
-        results = dao_get_last_template_usage(sms.id)
+        results = dao_get_last_template_usage(sms.id, 'sms')
         assert results.template.name == 'Template Name'
         assert results.template.template_type == 'sms'
         assert results.created_at == datetime(year=2000, month=1, day=1, hour=12, minute=0, second=0)
@@ -98,14 +98,14 @@ def test_should_be_able_to_get_all_template_usage_history_order_by_notification_
         notify_db,
         notify_db_session,
         sample_service):
-    sms = create_sample_template(notify_db, notify_db_session)
+    email = create_sample_template(notify_db, notify_db_session, template_type='email')
 
-    sample_notification(notify_db, notify_db_session, service=sample_service, template=sms)
+    sample_notification(notify_db, notify_db_session, service=sample_service, template=email)
-    sample_notification(notify_db, notify_db_session, service=sample_service, template=sms)
+    sample_notification(notify_db, notify_db_session, service=sample_service, template=email)
-    sample_notification(notify_db, notify_db_session, service=sample_service, template=sms)
+    sample_notification(notify_db, notify_db_session, service=sample_service, template=email)
-    most_recent = sample_notification(notify_db, notify_db_session, service=sample_service, template=sms)
+    most_recent = sample_notification(notify_db, notify_db_session, service=sample_service, template=email)
 
-    results = dao_get_last_template_usage(sms.id)
+    results = dao_get_last_template_usage(email.id, 'email')
     assert results.id == most_recent.id
 
 
@@ -135,7 +135,7 @@ def test_template_usage_should_ignore_test_keys(
         api_key=sample_test_api_key,
         key_type=KEY_TYPE_TEST)
 
-    results = dao_get_last_template_usage(sms.id)
+    results = dao_get_last_template_usage(sms.id, 'sms')
     assert results.id == team_key.id
 
 
@@ -144,7 +144,7 @@ def test_should_be_able_to_get_no_template_usage_history_if_no_notifications_usi
         notify_db_session):
     sms = create_sample_template(notify_db, notify_db_session)
 
-    results = dao_get_last_template_usage(sms.id)
+    results = dao_get_last_template_usage(sms.id, 'sms')
     assert not results