Re: [RFC PATCH 0/5] Add delta islands support

[Junio C Hamano <gitster@pobox.com>]

Jeff King <peff@peff.net> writes:

>    I think this is inherent in the scheme (we're losing some delta
>    opportunities). But I think it's also made worse because the delta
>    window gets clogged with candidates that are forbidden by the island
>    config.

Hmph, and the reason why objects that do not even belong to the same
island to be usable as a base are in the object list in the first
place is...?

>    Repacking with a big --window helps (and doesn't take as long
>    as it otherwise might because we can reject some object pairs based
>    on islands before doing any computation on the content).

Ah, then yes, a large window with early culling based on the delta
island criteria definitely sounds like the right solution to that
problem.

>    I have replacement code (which we have been running in production)
>    that is more clever about the threshold, and also can handle gaps in
>    the continuity (so we might realize we need to send objects 1-5000,
>    then skip a few, then 5037-8000, and so on).

That vaguely sounds similar to what folks at $DAYJOB runs in their
Gerrit/jgit thing.