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Merge pull request #3481 from manfre/ticket-16358
Fixed #16358 - Made memcache backend delete old value on a failure to set.
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a305695f28
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@ -86,7 +86,9 @@ class BaseMemcachedCache(six.with_metaclass(BaseMemcachedCacheMethods, BaseCache
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def set(self, key, value, timeout=DEFAULT_TIMEOUT, version=None):
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def set(self, key, value, timeout=DEFAULT_TIMEOUT, version=None):
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key = self.make_key(key, version=version)
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key = self.make_key(key, version=version)
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self._cache.set(key, value, self.get_backend_timeout(timeout))
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if not self._cache.set(key, value, self.get_backend_timeout(timeout)):
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# make sure the key doesn't keep its old value in case of failure to set (memcached's 1MB limit)
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self._cache.delete(key)
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def delete(self, key, version=None):
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def delete(self, key, version=None):
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key = self.make_key(key, version=version)
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key = self.make_key(key, version=version)
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@ -729,6 +729,10 @@ Miscellaneous
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.. _universal newlines: http://www.python.org/dev/peps/pep-0278
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.. _universal newlines: http://www.python.org/dev/peps/pep-0278
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* The Memcached cache backends ``MemcachedCache`` and ``PyLibMCCache`` will
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delete a key if ``set()`` fails. This is necessary to ensure the ``cache_db``
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session store always fetches the most current session data.
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.. _deprecated-features-1.8:
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.. _deprecated-features-1.8:
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Features deprecated in 1.8
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Features deprecated in 1.8
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@ -1133,6 +1133,24 @@ class MemcachedCacheTests(BaseCacheTests, TestCase):
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# culling isn't implemented, memcached deals with it.
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# culling isn't implemented, memcached deals with it.
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pass
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pass
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def test_memcached_deletes_key_on_failed_set(self):
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# By default memcached allows objects up to 1MB. For the cache_db session
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# backend to always use the current session, memcached needs to delete
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# the old key if it fails to set.
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# pylibmc doesn't seem to have SERVER_MAX_VALUE_LENGTH as far as I can
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# tell from a quick check of its source code. This is falling back to
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# the default value exposed by python-memcached on my system.
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max_value_length = getattr(cache._lib, 'SERVER_MAX_VALUE_LENGTH', 1048576)
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cache.set('small_value', 'a')
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self.assertEqual(cache.get('small_value'), 'a')
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large_value = 'a' * (max_value_length + 1)
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cache.set('small_value', large_value)
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# small_value should be deleted, or set if configured to accept larger values
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value = cache.get('small_value')
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self.assertTrue(value is None or value == large_value)
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@override_settings(CACHES=caches_setting_for_tests(
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@override_settings(CACHES=caches_setting_for_tests(
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BACKEND='django.core.cache.backends.filebased.FileBasedCache',
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BACKEND='django.core.cache.backends.filebased.FileBasedCache',
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