Re: Supercedes: header

    In order to help caches trim themselves, I propose a Supercedes: 
    header.
    
       Supercedes: URI
    
    A cache in receipt of a supercedes header could schedule the 
    referenced URI for early retirement.  It may not be instantly 
    obsolete as users may currently be displaying pages which reference 
    it, but it would likely not be useful to retain the entry for days.  
    The authority to issue this header could be limited to the 
    corresponding host to discourage malicious usage, but I wouldn't 
    bother. Such usage could not cause semantic transparency problems as 
    the URI is already exposed to being purged from the cache at any time 
    by the cache's replacement algorithm.
    
    This would allow caches to respond well to pages that are updated by 
    referring to new content (different URI) rather than just changing 
    the referred to content itself.
    
    This technique allows users that are on old copies of a page to 
    navigate to other content without surprises while new visitors to the 
    page see the most current references.  A news headlines page would be 
    a candidate for such usage.

I think this is an area that we ought to be thinking about, and
your suggestion seems initially attractive.  However, there may
be other ways to provide this kind of "replacement policy" support,
and I think it is premature to put this into HTTP/1.1.

I suggest holding the thought until we're done with the current
revision, and meanwhile perhaps someone should do some simulations
to see if this provides significant improvements in cache performance.

-Jeff

Received on Friday, 5 April 1996 20:44:44 UTC