On Thu, Sep 02, 2010 at 04:42:55PM +0100, Luke Kenneth Casson Leighton wrote:
> >> it seems to be. as long as each version of git produces the exact
> >> same pack object, off of the command "git pack-objects --all --stdout
> >> --thin {ref}< {objref}"
> >
> > This is not guaranteed.
> [...]
> * under what circumstances is it not guaranteed? and, crucially, is
> it necessary to care? i.e. if someone does a shallow git clone, i
> couldn't give a stuff.
pack-objects will reuse previously found deltas. So the deltas you have
in your existing packs matter. The deltas you have in your existing
packs depend on many things. At least:
1. Options you used when packing (e.g., --depth and --window).
2. Probably exactly _when_ you packed. You could find a good delta
from A to B. Later, object C comes into existence, and would
provide a better delta base for B. I don't think we will ever try A
against C, unless --no-reuse-delta is set.
You have a different pack than somebody who packed after A, B, and
C all existed.
In practice, this tends not to happen much because the best deltas
are usually going backwards in time to a previous version. But it
can happen.
-Peff
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