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From Issac Goldstand <mar...@beamartyr.net>
Subject Re: mod_cache responsibilities vs mod_xxx_cache provider responsibilities
Date Mon, 18 Sep 2006 15:50:28 GMT


Brian Akins wrote:
> Issac Goldstand wrote:
>   I can see how other tracking information (like how often the
>> cached entity is accessed, last access time, etc) would be useful,
>> albeit expensive to keep track of, but I don't understand this specific
>> example.
> 
> It's not expensive, as these methods are only called when an object to
> added or deleted, which is relatively few if you get good cache hit ratio.

Not necessarily.  The point would be to track "hot" objects so the
garbage collector prioritizes them lower than a fresher entry which
doesn't get accessed much.  Tracking information like that would need to
be done on every cache hit.  stating the file is enough to get the
initial creation time + last access time (which is why it makes sense,
to  me at least, to prefer the filesystem's atime overhead to trying to
out-do that code on our own)

> There are instances when you need to "purge" url's selectively.   Think
> a publishing system that automatically purges cache for updated pages,
> for example.
> 

Right.  But you can still do it with an open_entity() (which takes the
cache key and sets the filehandles and everything else in the
cache_handle) and then remove_entity.  My gut instinct tells me that
rewriting remove_entity to take the key instead of the cache_handle will
have side-effects of tracking whether the filehandles in the
cache_object are open or closed...

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