Re: Hit-metering: to Proposed Standard?

> Jeffrey Mogul:
> Finally, we agree that the usage-limiting aspect of the design
> is not as clearly useful as the hit-metering aspect.  But the
> draft hints at a few other useful things that it could be used
> for.  For example, it could be used with a (still-to-be-defined)
> prefetching mechanism so that a prefetched result could be cached
> for one use.  The existing "proxy-revalidate" mechanism in HTTP/1.1
> doesn't really work optimally for prefetched responses.

"not as clearly useful" is what has me worried. If it is not needed I do not 
want it. 

>     To illustrate the mesh problem: If I am a cache that gets handed 2
>     usages through my first parent and 4 through my second parent, do I
>     have to report back through the parent who gave me the usage-limit
>     or can I freely chose to report back through my third parent (who
>     has not connected to the origin server before and is likely to
>     report 4 out of zero and 2 out of zero or generally confuse the
>     origin server)? If I have to report through the appropriate parent,
>     this requires me to store where I got the document from; and it
>     heavily influences traffic patterns, robustness and the redundancy
>     of my mesh.
>     
> The question is meaningless because usage-limiting and hit-metering
> are independent, and usage-limiting does not require you to report
> anything.

The default use includes both usage-limiting and hit-metering, servers are 
likely to try to take advantage of the combination. If usage-limiting and 
hit-metering are independent, why have an example that shows how to use 
usage-limiting in combination with hit-metering? If a origin server hands out 
usages only to caches that do hit-metering; and cache-busting documents to the 
rest (I read your draft as suggesting this is a neat way to do it), then the 
combination does influence which parent I fetch documents from. The security 
aspects of this are interesting, because it may force unaware caches to 
channel their traffic through one branch of the mesh (and possibly take down 
the top cache server as it gets overloaded). If the origin server keeps track 
of what usage-limiting happens at different cache servers (as your example 
suggest), this is a bigger problem. 

> As I said in my response to Ted Hardie, our specification probably
> ought to say explicitly that the proxy needs to record the identity
> of the immediate source of a response, and this is another example
> where that is important.

How will this influence load-sharing?


Ingrid
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Received on Thursday, 21 November 1996 17:02:15 UTC