Re: GTP/0.1 terminology 101: commit reels and references

From: Sam Vilain <sam@vilain.net>
Date: Jul 29, 2008, 07:00 UTC
Message-ID: <1217314847.28919.98.camel@maia.lan>
In-Reply-To: <alpine.DEB.1.00.0807290014110.2725@eeepc-johanness>

On Tue, 2008-07-29 at 00:30 +0200, Johannes Schindelin wrote:

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> > Yes, but it is more defined than that.  There are still ambiguities with 
> > topological sort, so the gittorrent spec specified exactly how all ties 
> > are broken.  They happen to be a further refinement of --date-order, 
> > with respect to the ordering of commits.
> 
> But does that not mean that any new ref branching off of an ancient commit 
> changes all the pack boundaries?

No. A "References" object is a snapshot of all refs at a particular time. If you want to make a new ref you make a new "References" object. *all* of the new objects are contained in the new reel, and the new reels do not affect the old reels.

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> That should be easy, but I think that it would be _even better_ if we ask 
> pack-objects to generate several packs from the needed objects.  Ooops.  
> That already exists: 
> 
> 	$ git pack-objects --max-pack-size=<n>

This does not deterministically generate the same pack for a given set of refs across all git versions.

Your ideas would have been excellent earlier on, perhaps if developed they might have resulted in something quite a bit simpler with all of the features the current protocol has - but given we are in the second half of a GSoC project of which the end is in sight then I think we should shelve them until the project finishes. There has certainly been a lot of useful things come out of them!

Cheers, Sam.