Re: "Hits" pragma

Talking to several people privately, I've been convinced that  
"bundled request" reporting information would most naturally be  
placed into a Forwarded header, instead of a Pragma.  Forwarded  
headers have similar semantics to Pragmas (they accumulate and must  
be passed on down the line of proxies), and already represent a  
primitive form of reporting.

So, keeping in mind Brian Behlendorf's requirements list, here is a  
more refined proposal containing two extensions of the Forwarded  
header.  I think both should be considered, since they provide  
different balances between the demands of proxies and servers.

The first (proxy-biased) extension, which only requires constant  
storage per cached item at the proxy, adds a "count" clause to the  
Forwarded header:

	Forwarded: by http://proxy/ count 34

This is equivalent to the hits pragma, except that hit counts are   
assigned to specific "leaf" proxies.  To be precise:  The count is  
reset to zero after the proxy forwards a request.  Thereafter, every  
request for the resource received _without_ any Forwarded headers  
increases the count by one; every request _with_ one or more  
Forwarded headers simply contributes its Forwarded headers to the  
eventual list of headers to be submitted by the proxy.

The second extension, which supplies a more acceptable level of  
information, but at the cost of proxy storage proportional to the  
number of hits received, adds an "mfor" (multiple-for) clause to the  
Forwarded header:

	Forwarded: by http://proxy/ mfor Pr5CH77RbN7g0HTux90R7GHK

Here, the argument of the "mfor" clause is a compressed logfile,  
representing those requests received by the proxy for this resource  
since last forwarding, which did not contain any Forwarded headers  
of their own (as before, requests forwarded from proxies upstream  
simply contribute their own Forwarded headers).

What needs to be decided more precisely is (a) the compression  
algorithm to be applied to the logfile, and (b) the format and  
fields of the logfile.  Brian Behlendorf suggested a good minimum  
set of log fields:  host, timestamp, referer (although some sort of  
"host hiding" should probably be supported for privacy/security  
reasons).  Any suggestions for the compression?  It would be nice to  
have something that could be used incrementally by the proxy to  
save space.

Paul Burchard	<>
``I'm still learning how to count backwards from infinity...''

Received on Sunday, 13 August 1995 21:59:55 UTC