#35465: Feature: allow pre-caching and disable-cache
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Reporter: mdk | Owner: nobody
Type: New feature | Status: new
Component: Core (Cache system) | Version: 5.0
Severity: Normal | Keywords: cache
Triage Stage: Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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TL;DR: If there was a way to inhibit `cache.get()` (making it to always
return `default`), it would enable to use cases :
- One could implement a pre-caching tool like a simple curl in a crontab.
- One could implement a "disable cache" feature like the one in browsers
network panel, but applied server-side.
Longer explanation:
My initial idea is was to prefill the cache (say template fragments) using
a cron to guarantee cache hits for humans.
In the current Django, I can't do it: the cron would often just cache hit,
doing nothing, and a random human will cache miss and have a slower
request.
So I think I need a way to tell "if it's the pre-caching cron, don't try
to 'get' from the cache, just compute everything slowly, and fill the
cache with fresh data'.
And for this to work I « just need » to replace the real get during the
pre-caching step with:
def get(self, key, default=None, version=None):
return default
For example, if I have a 15mn cache with a 10mn cron, the cache will never
be close to expire, and it would be impossible for a user to cache miss.
Once this implemented, it could be "reused"/"recycled" as a "disable-
cache" feature: say for example the Django Debug Toolbar could have a
checkbox "disable cache", it would have the strange side effect to
populate the cache, but it would work as expected: the presented data
would be fresh.
Say we're going this way, it would need for a way to tell "this request is
without cache", like a cookie, a query string parameter, or whatever fits
in an HTTP request. If there's no concensus on how to flag this "cache
disabled" behavior it could be implemented as a dotted path to a function
returning a boolean, as SHOW_TOOLBAR_CALLBACK from Django debug toolbar.
There's a "security" catch to be aware of: if it's too easy to disable
cache on production servers, like `?cache=no` it could be used to DoS, it
probably has to be a tad more secure like by using a secret.
I have not tried to implement it, I'd like to discuss it before, so: does
it looks like a good idea? Has it been discussed many times before that I
missed maybe?
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Ticket URL: <https://code.djangoproject.com/ticket/35465>
Django <https://code.djangoproject.com/>
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