Re: delta encoding and state management

[Willy Tarreau <[e-mail]>]

On Thu, Jan 17, 2013 at 01:44:42PM -0800, James M Snell wrote:
> On Thu, Jan 17, 2013 at 1:35 PM, Roberto Peon <[e-mail]> wrote:
> 
> > Here are where my doubts stem from:
> >
> > "Custom" keys and values (cookies, user-agent strings, etc) are added to
> > headers and repeated basically all the time. If we don't know the input a
> > priori, we cannot construct a perfect or minimal encoding.
> >
> > Lets assume we do know about all of the possible header keys and values at
> > the time we create the spec.
> > Even then, we achieve something better than stateful compression only when
> > the sum-total of allowed permutations is less than the amount of bits you
> > need to toggle the visibility on a piece of state (which is very small
> > indeed).
> >
> 
> We certainly cannot come up with optimized binary encodings for everything
> but we can get a good ways down the road optimizing the parts we do know
> about. We've already seen, for instance, that date headers can be optimized
> significantly; and the separation of individual cookie crumbs allows us to
> keep from having to resend the entire cookie whenever just one small part
> changes. I'm certain there are other optimizations we can make without
> feeling like we have to find encodings for everything.

Yes indeed, have referrers relative to URI for example allows stateless
reduction in many cases (but not all) for pages composed of many objects.

Using single-byte for most well-known content types allows Accept to
send shorter lists.

Someone posted the WAP spec a few months ago, it was very useful because
all the research we're talking about was already done there. Even if it
needs some refreshing, the basic concepts of the web and the relation
between headers and their usual subsets of values generally remains.

Regards,
Willy