[Zope-PAS] RFC: PAS caching

[Jim Fulton]

Jens Vagelpohl wrote:
> Hi guys,
> 
> I'm going to work on caching for PAS and have thought about a couple 
> different architectural models to do so. I've come to a model I 
> personally like and wouldn't mind some comments.
> 
> Basically, I am proposing an architecture that works a little bit like 
> ZCacheable in that you instantiate cache managers and associate objects 
> (in this case plugins) with them. Obviously there are only a few plugin 
> types where it makes sense to cache anything. Since the "cacheable" 
> plugins have varying interfaces there would be specific cache manager 
> objects for each of them, and only the appropriate plugin can be 
> associated with them.
> 
> The plugins would cache based on keys that reflect the arguments to the 
> given method that is used to retrieve data and allow to set parameters 
> such as cache duration and knobs to invalidate the cache.
> 
> The caches require some cooperation from the plugins so that the methods 
> that provide cacheable data would try to locate and consult an 
> appropriate cache first, just like index_html in some basic OFS types 
> now consults ZCache_get before computing a result. The interfaces itself 
> would not be affected, just the implementations (which I would handle 
> myself, too).
> 
> What do you think?

Why isn't caching an implementation detail of the plugins?  Why do we need
a more general caching infrastructure within PAS?  In fact, plugins that
wanted to could use the existing Zope cache infrastructure.

Note that, based on discussions with Tres re caching, the Zope 3 PAS apis
specifically allow for caching of principals by principal factories. This
is why it is the responsibility of the cache factory to generate
principal-created events.  A cache factory might cache principal instances
and only generates principal-created events when it needs to compute a new
principal.


Jim

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