item expiration

Dustin Sallings dustin at
Thu Jun 12 04:37:59 UTC 2008

On Jun 11, 2008, at 18:02, Grant Maxwell wrote:

> 	If the class is cached and the record exists then we allow the  
> action to proceed.
> 	If the class is not cached then we just allow the action to proceed
> 	if the class is cached but the record does not exist then the  
> action is denied.

	Is there not a step like, ``if it's not cached, we need to look it  
up?''  If not, then it seems like you want something more along the  
lines of dynamo/chubby/zookeeper for these items.

	The proposals that make sense to me around LRU policies are more for  
QoS kinds of things.  That is, you can rate something between ``this  
is a little cheaper than recomputing it, but whatever'' to ``for the  
love of [deity] do not uncache this before the expiration date.''   
Even in the latter case, you must accept that the value *may* not be  
where you think it is and will need to be recomputed.

	The only time I really see making a business decision based on what  
value is in the cache is if you're under a heavy load scenario and are  
really trying to walk on eggshells around your centralized resource.   
e.g. you might give an HTTP 503 kind of response, but definitely  
nothing in the 400s.

Dustin Sallings

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