diff options
| -rw-r--r-- | django/core/cache/backends/memcached.py | 4 | ||||
| -rw-r--r-- | docs/releases/1.8.txt | 4 | ||||
| -rw-r--r-- | tests/cache/tests.py | 18 |
3 files changed, 25 insertions, 1 deletions
diff --git a/django/core/cache/backends/memcached.py b/django/core/cache/backends/memcached.py index b32ab704ec..87f05f973b 100644 --- a/django/core/cache/backends/memcached.py +++ b/django/core/cache/backends/memcached.py @@ -86,7 +86,9 @@ class BaseMemcachedCache(six.with_metaclass(BaseMemcachedCacheMethods, BaseCache def set(self, key, value, timeout=DEFAULT_TIMEOUT, version=None): key = self.make_key(key, version=version) - self._cache.set(key, value, self.get_backend_timeout(timeout)) + if not self._cache.set(key, value, self.get_backend_timeout(timeout)): + # make sure the key doesn't keep its old value in case of failure to set (memcached's 1MB limit) + self._cache.delete(key) def delete(self, key, version=None): key = self.make_key(key, version=version) diff --git a/docs/releases/1.8.txt b/docs/releases/1.8.txt index d3232d8235..fec2e2b4bc 100644 --- a/docs/releases/1.8.txt +++ b/docs/releases/1.8.txt @@ -729,6 +729,10 @@ Miscellaneous .. _universal newlines: http://www.python.org/dev/peps/pep-0278 +* The Memcached cache backends ``MemcachedCache`` and ``PyLibMCCache`` will + delete a key if ``set()`` fails. This is necessary to ensure the ``cache_db`` + session store always fetches the most current session data. + .. _deprecated-features-1.8: Features deprecated in 1.8 diff --git a/tests/cache/tests.py b/tests/cache/tests.py index c7604f131e..9dfd7af15d 100644 --- a/tests/cache/tests.py +++ b/tests/cache/tests.py @@ -1133,6 +1133,24 @@ class MemcachedCacheTests(BaseCacheTests, TestCase): # culling isn't implemented, memcached deals with it. pass + def test_memcached_deletes_key_on_failed_set(self): + # By default memcached allows objects up to 1MB. For the cache_db session + # backend to always use the current session, memcached needs to delete + # the old key if it fails to set. + # pylibmc doesn't seem to have SERVER_MAX_VALUE_LENGTH as far as I can + # tell from a quick check of its source code. This is falling back to + # the default value exposed by python-memcached on my system. + max_value_length = getattr(cache._lib, 'SERVER_MAX_VALUE_LENGTH', 1048576) + + cache.set('small_value', 'a') + self.assertEqual(cache.get('small_value'), 'a') + + large_value = 'a' * (max_value_length + 1) + cache.set('small_value', large_value) + # small_value should be deleted, or set if configured to accept larger values + value = cache.get('small_value') + self.assertTrue(value is None or value == large_value) + @override_settings(CACHES=caches_setting_for_tests( BACKEND='django.core.cache.backends.filebased.FileBasedCache', |