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RE: Re-work of op-code patterns

From: RUELLAN Herve <Herve.Ruellan@crf.canon.fr>
Date: Wed, 12 Feb 2014 11:57:25 +0000
To: RUELLAN Herve <Herve.Ruellan@crf.canon.fr>, Martin Thomson <martin.thomson@gmail.com>, Jeff Pinner <jpinner@twitter.com>
CC: "ietf-http-wg@w3.org" <ietf-http-wg@w3.org>
Message-ID: <59029012-5077-4b0a-b65a-8c5963465c4d@ADELE.crf.canon.fr>
I'm somewhat annoyed of using two bytes to clear the reference set: this decrease the usefulness of it, and I think it can be very useful in the aggregating proxy use-case.

However, I agree that changing the op-codes may not be the best solution. But there's another possibility:
- use index 0 to encode that the reference set is cleared.
- use the first index after the static table to encode that the header table size is changed.

As a result, we need only one byte to clear the reference set. For changing the header table size, one or two bytes will be needed in addition of encoding the actual new size. This is possibly a slight increase in size, but I think that header table size change will not be very common.

If there's no strong opinion against this, I'd like to include it in HPACK-06 which is almost ready to go.

Hervé.

> -----Original Message-----
> From: RUELLAN Herve [mailto:Herve.Ruellan@crf.canon.fr]
> Sent: mardi 28 janvier 2014 18:05
> To: Martin Thomson; Jeff Pinner
> Cc: ietf-http-wg@w3.org
> Subject: RE: Re-work of op-code patterns
> 
> I ran the number, but they were maybe hidden at the end of my proposal.
> Here there are again, with more details:
> 
> Mnot test set:
> 		Req	Res	All
> Current		24,62%	37,53%	29,62%
> Proposal	24,66%	37,53%	29,64%
> 
> Hruellan test set:
> 		Req	Res	All
> Current		17,89%	26,34%	21,65%
> Proposal	17,96%	26,34%	21,68%
> 
> So there is a compaction loss, but it's mostly negligible.
> 
> It is also probably easier for handling padding inside HPACK.
> 
> Hervé.
> 
> > -----Original Message-----
> > From: Martin Thomson [mailto:martin.thomson@gmail.com]
> > Sent: lundi 27 janvier 2014 18:39
> > To: Jeff Pinner
> > Cc: RUELLAN Herve; ietf-http-wg@w3.org
> > Subject: Re: Re-work of op-code patterns
> >
> > On 27 January 2014 08:43, Jeff Pinner <jpinner@twitter.com> wrote:
> > > With the proposed change what would 0b1000000 signal?
> >
> > An indexed header field, the first one.
> >
> > > If we are going to add a new opcode, I'd prefer to see the literal header
> > > encodes both start with the same symbol:
> >
> > The problem with your proposal is that it takes a rare condition
> > (Encoding context change) and assigns a shorter opcode to it.  The
> > cost is that header indexes greater than 30 will take an extra byte.
> > If you really want this, run the numbers and let us know what it
> > costs.
Received on Wednesday, 12 February 2014 11:57:56 UTC

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