#15201: CACHE_MIDDLEWARE_ANONYMOUS_ONLY is ugly, misleading, and unnecessary,
and
should be deprecated
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Reporter: carljm | Owner: nobody
Status: new | Milestone:
Component: Cache system | Version: SVN
Keywords: | Triage Stage: Unreviewed
Has patch: 0 |
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From https://github.com/django/django/pull/4:
{{{
There are three supposed benefits of using the cache middleware with
CACHE_MIDDLEWARE_ANONYMOUS_ONLY set to True:
1) Don't show user-specific data to the wrong users.
2) Avoid wasting memory on caching user-specific pages.
3) Improve performance by caching most pages.
}}}
(1) is unnecessary: Django already sets Vary: Cookie headers when the
session is accessed, which will prevent users from getting another user's
cached pages. In fact one danger of the current documentation of
CACHE_MIDDLEWARE_ANONYMOUS_ONLY is that it does not mention Vary: Cookie
and may mislead users into thinking that CACHE_MIDDLEWARE_ANONYMOUS_ONLY
is necessary to avoid users being shown wrong cached pages.
CACHE_MIDDLEWARE_ANONYMOUS_ONLY is only partially effective at (2),
because it will still cache session-specific pages with Vary: Cookie if a
user is not logged in, which can blow up caching memory just as much or
more as authenticated requests, if sessions are used with anonymous users.
And on the downside, CACHE_MIDDLEWARE_ANONYMOUS_ONLY is far from simple:
it requires contrib.auth to be installed before it can be used, and is
tricky to implement correctly (until the fix for #13283 was committed, the
incorrect implementation in place for years meant that turning
CACHE_MIDDLEWARE_ANONYMOUS_ONLY on immediately destroyed caching
efficiency for your entire site, including anonymous pages).
An alternative hypothetical setting, CACHE_MIDDLEWARE_SKIP_VARY_COOKIE,
would give users a more accurate model of how caching actually works,
would remove both the complexity of implementation and the needless
dependence on contrib.auth, and would be more effective at improving
caching efficiency (because it would also avoid caching session-dependent-
but-anonymous requests).
I think this behavior change should be made in any case; it's a clear
improvement with no downside that I can see. It would be possible to make
the behavior change and leave the current (somewhat misleading) setting
name, to avoid deprecation churn. I think I lean towards going ahead and
changing the name of the setting too; based on the lack of outcry around
#13283 I get the impression few users are using
CACHE_MIDDLEWARE_ANONYMOUS_ONLY anyway, and it's a painless setting name
switch.
Thanks to natrius in the above pull request and the #13283 comments for
these observations.
--
Ticket URL: <http://code.djangoproject.com/ticket/15201>
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