Re: Huge win, compressing a window of delta runs as a unit

[Nicolas Pitre <nico@cam.org>]

On Thu, 17 Aug 2006, Jon Smirl wrote:

> Is there a pack format version number built into the server procotol?
> If not there needs to be one. When there is a mismatch with the server
> pack version the client should simply display an error requesting an
> upgrade of the client software.

There is a pack version number.  Reception of an unknown pack already 
produces an error:

        if (!pack_version_ok(hdr->hdr_version))
                die("unknown pack file version %d", ntohl(hdr->hdr_version));

That will occur really early in a pull or clone when using the native 
protocol.

> Git should be designed for forward evolution, not infinite backward
> compatibility. It is easy to upgrade your client to support the new
> protocol. The protocol just needs to ensure that the client reliably
> gets an error about the need to upgrade.
> 
> Forward evolution implies that a client is able to work with older
> servers, but not the inverse, that new servers have to work with old
> clients.

And still, if we really wanted, the server could have the ability to 
stream an old pack format by simply inflating the grouped objects and 
deflating them individually all on the fly, which is not necessarily 
that costly.  But it might still be a good idea to simply have the 
ability to generate both formats and make the grouped deltas the default 
only after a while.


Nicolas