Only use in-memory cache for database settings, set ttl=5 (#12166)

* Only use in-memory cache for database settings

Make necessary adjustments to monkeypatch
  as it is very vunerable to recursion
  Remove migration exception that is now redundant

Clear cache if a setting is changed

* Use dedicated middleware for setting cache stuff
  Clear cache for each request

* Add tests for in-memory cache

awx/conf/settings.py

@@ -1,7 +1,6 @@
 # Python
 import contextlib
 import logging
-import sys
 import threading
 import time
 import os
@@ -31,7 +30,7 @@ from awx.conf.models import Setting
 
 logger = logging.getLogger('awx.conf.settings')
 
-SETTING_MEMORY_TTL = 5 if 'callback_receiver' in ' '.join(sys.argv) else 0
+SETTING_MEMORY_TTL = 5
 
 # Store a special value to indicate when a setting is not set in the database.
 SETTING_CACHE_NOTSET = '___notset___'
@@ -403,11 +402,15 @@ class SettingsWrapper(UserSettingsHolder):
         key=lambda *args, **kwargs: SettingsWrapper.hashkey(*args, **kwargs),
         lock=lambda self: self.__dict__['_awx_conf_memoizedcache_lock'],
     )
+    def _get_local_with_cache(self, name):
+        """Get value while accepting the in-memory cache if key is available"""
+        with _ctit_db_wrapper(trans_safe=True):
+            return self._get_local(name)
+
     def __getattr__(self, name):
         value = empty
         if name in self.all_supported_settings:
-            with _ctit_db_wrapper(trans_safe=True):
-                value = self._get_local(name)
+            value = self._get_local_with_cache(name)
         if value is not empty:
             return value
         return self._get_default(name)

awx/conf/signals.py

@@ -28,6 +28,9 @@ def handle_setting_change(key, for_delete=False):
     cache_keys = {Setting.get_cache_key(k) for k in setting_keys}
     cache.delete_many(cache_keys)
 
+    # if we have changed a setting, we want to avoid mucking with the in-memory cache entirely
+    settings._awx_conf_memoizedcache.clear()
+
     # Send setting_changed signal with new value for each setting.
     for setting_key in setting_keys:
         setting_changed.send(sender=Setting, setting=setting_key, value=getattr(settings, setting_key, None), enter=not bool(for_delete))

awx/conf/tests/unit/test_settings.py

@@ -8,6 +8,8 @@ import codecs
 from uuid import uuid4
 import time
 
+from unittest import mock
+
 from django.conf import LazySettings
 from django.core.cache.backends.locmem import LocMemCache
 from django.core.exceptions import ImproperlyConfigured
@@ -299,3 +301,33 @@ def test_readonly_sensitive_cache_data_is_encrypted(settings):
     cache.set('AWX_ENCRYPTED', 'SECRET!')
     assert cache.get('AWX_ENCRYPTED') == 'SECRET!'
     assert native_cache.get('AWX_ENCRYPTED') == 'FRPERG!'
+
+
+@pytest.mark.defined_in_file(AWX_VAR='DEFAULT')
+def test_in_memory_cache_only_for_registered_settings(settings):
+    "Test that we only make use of the in-memory TTL cache for registered settings"
+    settings._awx_conf_memoizedcache.clear()
+    settings.MIDDLEWARE
+    assert len(settings._awx_conf_memoizedcache) == 0  # does not cache MIDDLEWARE
+    settings.registry.register('AWX_VAR', field_class=fields.CharField, category=_('System'), category_slug='system')
+    settings._wrapped.__dict__['all_supported_settings'] = ['AWX_VAR']  # because it is cached_property
+    settings._awx_conf_memoizedcache.clear()
+    assert settings.AWX_VAR == 'DEFAULT'
+    assert len(settings._awx_conf_memoizedcache) == 1  # caches registered settings
+
+
+@pytest.mark.defined_in_file(AWX_VAR='DEFAULT')
+def test_in_memory_cache_works(settings):
+    settings._awx_conf_memoizedcache.clear()
+    settings.registry.register('AWX_VAR', field_class=fields.CharField, category=_('System'), category_slug='system')
+    settings._wrapped.__dict__['all_supported_settings'] = ['AWX_VAR']
+
+    settings._awx_conf_memoizedcache.clear()
+
+    with mock.patch('awx.conf.settings.SettingsWrapper._get_local', return_value='DEFAULT') as mock_get:
+        assert settings.AWX_VAR == 'DEFAULT'
+        mock_get.assert_called_once_with('AWX_VAR')
+
+    with mock.patch.object(settings, '_get_local') as mock_get:
+        assert settings.AWX_VAR == 'DEFAULT'
+        mock_get.assert_not_called()