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Diffstat (limited to 'docs')
| -rw-r--r-- | docs/topics/cache.txt | 39 |
1 files changed, 39 insertions, 0 deletions
diff --git a/docs/topics/cache.txt b/docs/topics/cache.txt index e5ca526494..5797199411 100644 --- a/docs/topics/cache.txt +++ b/docs/topics/cache.txt @@ -641,6 +641,45 @@ nonexistent cache key.:: However, if the backend doesn't natively provide an increment/decrement operation, it will be implemented using a two-step retrieve/update. +Cache key warnings +------------------ + +.. versionadded:: 1.3 + +Memcached, the most commonly-used production cache backend, does not allow +cache keys longer than 250 characters or containing whitespace or control +characters, and using such keys will cause an exception. To encourage +cache-portable code and minimize unpleasant surprises, the other built-in cache +backends issue a warning (``django.core.cache.backends.base.CacheKeyWarning``) +if a key is used that would cause an error on memcached. + +If you are using a production backend that can accept a wider range of keys (a +custom backend, or one of the non-memcached built-in backends), and want to use +this wider range without warnings, you can silence ``CacheKeyWarning`` with +this code in the ``management`` module of one of your +:setting:`INSTALLED_APPS`:: + + import warnings + + from django.core.cache import CacheKeyWarning + + warnings.simplefilter("ignore", CacheKeyWarning) + +If you want to instead provide custom key validation logic for one of the +built-in backends, you can subclass it, override just the ``validate_key`` +method, and follow the instructions for `using a custom cache backend`_. For +instance, to do this for the ``locmem`` backend, put this code in a module:: + + from django.core.cache.backends.locmem import CacheClass as LocMemCacheClass + + class CacheClass(LocMemCacheClass): + def validate_key(self, key): + """Custom validation, raising exceptions or warnings as needed.""" + # ... + +...and use the dotted Python path to this module as the scheme portion of your +:setting:`CACHE_BACKEND`. + Upstream caches =============== |