Re: Straw Poll: Restore Header Table and Static Table Indices

[Willy Tarreau <[e-mail]>]

Hi Greg,

On Wed, Oct 22, 2014 at 12:36:30AM +1100, Greg Wilkins wrote:
> Willy,
> 
> I actually think that literal without/never indexed should be favoured over
> literal indexed or at least on event footing, because by nature the literal
> indexed headers are sent only once and then used by index, while the
> literal without/never indexed headers are sent literally every time they
> are used.

OK, thanks for explaining.

> Thus I would think something like:
> 
> Indexed Header:
>    +---+---+---+---+---+---+---+---+
>    | 1 | D |    Index (6+)         |
>    +---+---------------------------+

Here we still have the 20% waste I wanted to address : ~48/256 values
will never be sent (those for static entries >16). That's where I
wanted to recover that many values (5.5 bits) which are clearly
missing from other encodings.

> Literal Never Indexed:
>    +---+---+---+---+---+---+---+---+
>    | 0 | 0 | 0 | D | Index (4+)    |
>    +---+---------------------------+
> 
> Literal Not Indexed:
>    +---+---+---+---+---+---+---+---+
>    | 0 | 0 | 1 | D | Index (4+)    |
>    +---+---------------------------+
> 
> Literal Indexed:
>    +---+---+---+---+---+---+---+---+
>    | 0 | 1 | 0 | D | Index (4+)    |
>    +---+---------------------------+

Two of them can then be increased by 1..1.5 bit by recovering
the unused encoding above.

> Max Dynamic Table size change:
>    +---+---+---+---+---+---+---+---+
>    | 0 | 1 | 1 |  Index (5+)       |
>    +---+---------------------------+

And this one looks like a huge waste to me, it only happens
once in a long while and kills 32 possible values that we'd
better use for each individual header. In practice, 80/256
code points are unusable for each header, that's roughly 33%
wasted encoding space :-/.

> I believe that most 62 static slots can easily be filled with values that
> will be used.

That's where I'm really doubting to be honnest.

> I'll come up with a suggestion for this tomorrow.

OK great!

Cheers,
Willy