#6124: need a non-pickled locmem cache backend
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Reporter: [EMAIL PROTECTED] | Owner: nobody
Status: new | Milestone:
Component: Cache system | Version: SVN
Resolution: | Keywords: cache, locmem, pickle
Stage: Accepted | Has_patch: 1
Needs_docs: 0 | Needs_tests: 0
Needs_better_patch: 1 |
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Comment (by Pascal Varet <[EMAIL PROTECTED]>):
Hello Luke,
I can see a few problems with your patch:
- Well, to start with, it's not a patch. :) You want to give a patch,
rather than the patched file itself, for two reasons: one, the file may
have received other changes than your own since, so it's important to
provide only those lines that you did change, and two, in a patch you can
provide changes to several files, which, as you'll see below, is relevent
to this case.
- Your patch should provide documentation for the option you are adding to
the locmem cache backend. (That's where you need to provide changes to
another file.) On that note, you should absolutely document the fact that
your new option breaks the convention that cached object be picklable (see
the current cache documentation).
- Your patch should provide tests. I'm very much not an expert on tests,
but I think what you should provide is tests that ensure a non-picklable
object is cached when the option nopickle=true is given, and not cached
otherwise.
- Lastly: your patch contains a subtle bug: since you return the same
object whenever the cache is called, if any caller modifies the object for
its own purpose, then the object is modified for every caller. This is
typically bad in the case of cached HTTP responses. See ticket #599, which
addressed this very same issue back then. This issue is the reason why
pickling was used in the first place, so presumably your patch should
provide another, non-pickle-based solution to the same problem.
All this being said, IMHO, your problem (object persistence) is not the
one that the Django cache exists to solve. In the Django cache, attempts
to cache uncacheable objects fail silently, and cached object eventually
expire -- neither are what you need, right?
Perhaps the best solution for you would be to implement your own object
persistence. See, what the locmem cache amounts to is a simple old Python
dictionary with locks and expiration. Since, unless I'm mistaken, you
don't need expiration, perhaps a dictionary somewhere is all you need? The
dictionary will be persisted as long as your Django app keeps running,
exactly as with the locmem cache backend.
HTH.
--
Ticket URL: <http://code.djangoproject.com/ticket/6124#comment:3>
Django Code <http://code.djangoproject.com/>
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