Re: [PATCH] git exproll: steps to tackle gc aggression

From: Ramkumar Ramachandra <artagnon@gmail.com>
Date: Aug 8, 2013, 19:14 UTC
Message-ID: <CALkWK0mE=Gov1YocbGMs4cUGf+-uEorvkFwBEpP0JXfDLPwuyQ@mail.gmail.com>
In-Reply-To: <7va9ks9frm.fsf@alter.siamese.dyndns.org>

Junio C Hamano wrote:

Show 11 quoted lines

> Martin Fick <mfick@codeaurora.org> writes:
>> Assuming I understand what you are suggesting, would these
>> "young object" likely still get "deduped" in an efficient
>> way without doing history traversal (it sounds like they
>> would)?
>
> Yes.
>
> The very first thing pack-object machinery does is to get the list
> of object names and sort them in a certain order to help producing
> good deltas, and this initial input preprocessing will dedup them.

So, the proposal is to create an index of young objects without doing reachability analysis (I still didn't get the point of packing them; as I pointed out, it seems to be rather counter-productive) to help the actual packing? From what I vaguely understood:

1. Index all the young objects to save a history traversal (?)

2. Perform the reachability analysis using the index in step 1, and
then generate the pack.

I'm not yet clear about what information 1 contains to help 2. Is it the rough ordering? (The big important objects come near the top of the pack, and the deltas are generated against them). I say "rough" because the ordering might change after the unreachable objects are pruned.

*scratches head*