On Sun, Aug 18, 2013 at 1:59 PM, Stephan Beal <sgb...@googlemail.com> wrote:
> On Sun, Aug 18, 2013 at 10:53 AM, Isaac Jurado <dipto...@gmail.com> wrote:
>> It's about backwards compatibility.  Fossil will not generate delta
>> manifest on commit unless there already are delta manifest on the
>> repository or you force it on the command line.
> i had no idea there was a --delta option to commit - thanks for that tip.
>> I guess that almost all Fossil binaries in use now understand B cards,
>> but as no one has committed to the Fossil repository with the
>> "--delta" option yet, you will not find any delta manifest in it.
> i don't want to be the first one to try ;), but i will use it on my the
> libfossil repo for testing.
>> Delta manifests are quite interesting because they follow the same
>> design concepts as Mercurial's delta storage.  I have already
>> mentioned it, but I have a Fossil branch that can generate delta
>> manifests on import.  However, I still don't have any place to publish
>> it.
> i don't yet understand the benefit of a delta manifest except that they save
> a few hundred (or thousand) lines of F-cards.
> Do you know if it's possible to have a delta of a delta, or is a delta
> always from a non-delta manifest? Parts of the code treat them as if there
> can be any number of them (recursive cleanup in manifest_destroy()), but
> some parts seem to imply that a delta cannot derive from a delta
> (manifest_file_next()).

As far as I've seen, delta manifest cannot be chained.  There is a
formula in the commit code that determines if a delta manifest is
worth using or not.  Therefore, when the parent of a delta manifest is
also a delta manifest, it will contain the F cards from the parent,
plus its own.

> If you have a repo with deltas, may i have a copy of it? It would be very
> useful for testing my delta manifest code.

I tested my improved import branch with the Django git repository,
which turned out contain a couple of very interesting cases I wasn't
even aware of when developing the first patches.  These imported
repositories weight almost 200MB, so I think it is better that I
manage to publish my branch so you can import whatever you want.

Isaac Jurado

"The noblest pleasure is the joy of understanding"
Leonardo da Vinci
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