Re: delta encoding and state management

[Nico Williams <[e-mail]>]

On Thu, Jan 17, 2013 at 3:44 PM, James M Snell <[e-mail]> wrote:
> 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.

The only way cookie compression can work is by having connection
state.  But often the whole point of cookies is to not store state on
the server but on the client.

The more state we associate with connections the more pressure there
will be to close connections sooner and then we'll have to establish
new connections, build new compression state, and then have it torn
down again.  Fast TCP can help w.r.t. reconnect overhead, but that's
about it.

We need to do more than measure compression ratios.  We need to
measure state size and performance impact on fully-loaded middleboxes.
 We need to measure the full impact of compression on the user
experience.  A fabulous compression ratio might nonetheless spell doom
for the user experience and thence the protocol.  If we take the wrong
measures we risk failure for the new protocol, and we may not try
again for a long time.

Also, with respect to some of those items we cannot encode minimally
(cookies, URIs, ...): their size is really in the hands of the
entities that create them -- let *them* worry about compression.  That
might cause some pressure to create shorter, less-meaningful URIs,
but... we're already there anyways.

Nico
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