Re: [PATCH] diff-delta: produce optimal pack data

From: Junio C Hamano <junkio@cox.net>
Date: Feb 24, 2006, 20:53 UTC
Message-ID: <7vpslc8oni.fsf@assigned-by-dhcp.cox.net>
In-Reply-To: <Pine.LNX.4.64.0602241152290.22647@g5.osdl.org>

Linus Torvalds <torvalds@osdl.org> writes:

Show 6 quoted lines

> NOTE! Every SINGLE one of those heuristics are just totally made up by 
> yours truly, and have no testing behind them. They're more of the type 
> "that sounds about right" than "this is how it must be". As mentioned, 
> Nico has already been playing with the heuristics - but he wanted better 
> packs, not better CPU usage, so he went the other way from what you would 
> want to try..

I haven't looked at Nico's original or updated code closely at all, but two things come to mind.

(1) if we could tell the particular data is intrinsically
    diff_delta unfriendly and diff_delta would waste too much
    time when tried to delta against almost _any_ other blob,
    then it might help to give an interface in diff-delta.c for
    the caller to check for such a blob without even trying
    diff_delta.

(2) otherwise, if diff_delta could detect it would spend too
    many cycles to finish its work for a particular input early
    on, we might want it to bail out instead of trying a
    complete job.