Tightened the error checking.

- Looks now for a specific Integrity error, not a generic SQLAlchemy  error when checking for an insert failure
- If the update fails post an insert error, then there is an issue so raise an exception so tasks can be retried.

app/dao/statistics_dao.py

@@ -1,5 +1,5 @@
 from flask import current_app
-from sqlalchemy.exc import SQLAlchemyError
+from sqlalchemy.exc import IntegrityError, SQLAlchemyError
 
 from app import db
 from app.dao.dao_utils import transactional
@@ -15,14 +15,14 @@ from app.statsd_decorators import statsd
 
 
 @statsd(namespace="dao")
-@transactional
 def create_or_update_job_sending_statistics(notification):
     if __update_job_stats_sent_count(notification) == 0:
         try:
             __insert_job_stats(notification)
-        except SQLAlchemyError as e:
+        except IntegrityError as e:
             current_app.logger.exception(e)
-            __update_job_stats_sent_count(notification)
+            if __update_job_stats_sent_count(notification) == 0:
+                raise SQLAlchemyError("Failed to create job statistics for {}".format(notification.job_id))
 
 
 def __update_job_stats_sent_count(notification):
@@ -39,6 +39,7 @@ def __update_job_stats_sent_count(notification):
     ).update(update)
 
 
+@transactional
 def __insert_job_stats(notification):
 
     stats = JobStatistics(

tests/app/dao/test_statistics_dao.py

@@ -1,7 +1,7 @@
 from unittest.mock import call
 
 import pytest
-from sqlalchemy.exc import SQLAlchemyError
+from sqlalchemy.exc import IntegrityError, SQLAlchemyError
 
 from app.dao.statistics_dao import (
     create_or_update_job_sending_statistics,
@@ -126,18 +126,22 @@ def test_should_update_a_stats_entry_for_a_job(
     assert stat.letters_failed == 0
 
 
-def test_should_handle_case_where_stats_row_created_by_another_thread(
+def test_should_handle_error_conditions(
         notify_db,
         notify_db_session,
-        sample_notification,
+        sample_job,
         mocker):
-    create_mock = mocker.patch("app.dao.statistics_dao.__insert_job_stats", side_effect=SQLAlchemyError("beaten to it"))
+    create_mock = mocker.patch("app.dao.statistics_dao.__insert_job_stats", side_effect=IntegrityError("1", "2", "3"))
     update_mock = mocker.patch("app.dao.statistics_dao.__update_job_stats_sent_count", return_value=0)
 
-    create_or_update_job_sending_statistics(sample_notification)
+    notification = sample_notification(notify_db, notify_db_session, job=sample_job)
 
-    update_mock.assert_has_calls([call(sample_notification), call(sample_notification)])
-    create_mock.assert_called_once_with(sample_notification)
+    with pytest.raises(SQLAlchemyError) as e:
+        create_or_update_job_sending_statistics(notification)
+    assert 'Failed to create job statistics for {}'.format(sample_job.id) in str(e.value)
+
+    update_mock.assert_has_calls([call(notification), call(notification)])
+    create_mock.assert_called_once_with(notification)
 
 
 @pytest.mark.parametrize('notification_type, sms_count, email_count, letter_count', [