[Zope-CMF] [Warning] Danger from Zope caching, especially the CMF Caching Policy Manager

Jens Vagelpohl jens at dataflake.org
Sun Dec 17 13:57:20 EST 2006


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On 17 Dec 2006, at 18:52, Dieter Maurer wrote:
> The description indicates in what direction the CPM should get fixed:
>
>   * If the response already provides cache control, the CPM should
>     not override it, as it is likely that the specific information
>     available to the response generating process is more trustworthy
>     then the general CPM policies.
>
>     This is arguable, especially as it changes the current behaviour.
>     Maybe, it should be controlled by an additional configuration  
> option.

I don't know if it is possible to have any sane policy about "what to  
do if the response already has caching headers". First of all, when  
should this exception policy trigger? Which headers should tell the  
CPM that someone else already decided on caching? Secondly, what is  
the behavior supposed to be? "Do nothing"? "DWIM"? This obviously  
needs exact specifications and use cases.


>   * The CPM (and Zope's HTTP Cache Manager) must set cache headers
>     only based on the object that generated the (complete) response
>     entity and not based on other objects called during the request
>     (and probably only responsible for part of the entity).

As mentioned in my reply to your collector issue, there are fixes on  
the CMF trunk already and you should look at those to see if they fix  
your problem.

jens


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