From 87afc439fe7451a1178b68b1bbee3efab66766aa Mon Sep 17 00:00:00 2001
From: Chris Hill-Scott <me@quis.cc>
Date: Mon, 22 Jun 2020 09:39:46 +0100
Subject: [PATCH] Cache serialised template in memory

---
 app/serialised_models.py                      | 25 +++++++++++++++++
 .../notifications/test_post_notifications.py  | 28 +++++++++++++++++++
 2 files changed, 53 insertions(+)

diff --git a/app/serialised_models.py b/app/serialised_models.py
index f864171f7..1896c1810 100644
--- a/app/serialised_models.py
+++ b/app/serialised_models.py
@@ -1,7 +1,31 @@
 from abc import ABC, abstractmethod
+from collections import defaultdict
+from functools import partial
+from threading import RLock
+
+import cachetools
 
 from app.dao import templates_dao
 
+caches = defaultdict(partial(cachetools.TTLCache, maxsize=1024, ttl=2))
+locks = defaultdict(RLock)
+
+
+def memory_cache(func):
+    @cachetools.cached(
+        cache=caches[func.__qualname__],
+        lock=locks[func.__qualname__],
+        key=ignore_first_argument_cache_key,
+    )
+    def wrapper(*args, **kwargs):
+        return func(*args, **kwargs)
+
+    return wrapper
+
+
+def ignore_first_argument_cache_key(cls, *args, **kwargs):
+    return cachetools.keys.hashkey(*args, **kwargs)
+
 
 class SerialisedModel(ABC):
 
@@ -40,6 +64,7 @@ class SerialisedTemplate(SerialisedModel):
     }
 
     @classmethod
+    @memory_cache
     def from_id_and_service_id(cls, template_id, service_id):
         return cls(cls.get_dict(template_id, service_id))
 
diff --git a/tests/app/v2/notifications/test_post_notifications.py b/tests/app/v2/notifications/test_post_notifications.py
index 7fe8acc0a..4348ae24d 100644
--- a/tests/app/v2/notifications/test_post_notifications.py
+++ b/tests/app/v2/notifications/test_post_notifications.py
@@ -6,6 +6,7 @@ import pytest
 from freezegun import freeze_time
 from boto.exception import SQSError
 
+from app.dao import templates_dao
 from app.dao.service_sms_sender_dao import dao_update_service_sms_sender
 from app.models import (
     ScheduledNotification,
@@ -211,6 +212,33 @@ def test_notification_reply_to_text_is_original_value_if_sender_is_changed_after
     assert notifications[0].reply_to_text == '123456'
 
 
+def test_should_cache_template_lookups_in_memory(mocker, client, sample_template):
+
+    mock_get_template = mocker.patch(
+        'app.dao.templates_dao.dao_get_template_by_id_and_service_id',
+        wraps=templates_dao.dao_get_template_by_id_and_service_id,
+    )
+    mocker.patch('app.celery.provider_tasks.deliver_sms.apply_async')
+
+    data = {
+        'phone_number': '+447700900855',
+        'template_id': str(sample_template.id),
+    }
+
+    for i in range(5):
+        auth_header = create_authorization_header(service_id=sample_template.service_id)
+        client.post(
+            path='/v2/notifications/sms',
+            data=json.dumps(data),
+            headers=[('Content-Type', 'application/json'), auth_header]
+        )
+
+    assert mock_get_template.call_args_list == [
+        call(service_id=sample_template.service_id, template_id=str(sample_template.id))
+    ]
+    assert Notification.query.count() == 5
+
+
 @pytest.mark.parametrize("notification_type, key_send_to, send_to",
                          [("sms", "phone_number", "+447700900855"),
                           ("email", "email_address", "sample@email.com")])