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From: Jeff King <peff@peff.net>
Subject: Re: push race
Date: Tue, 16 Oct 2012 13:25:02 -0400
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Cc: Nguyen Thai Ngoc Duy <pclouds@gmail.com>,
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To: Junio C Hamano <gitster@pobox.com>
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On Tue, Oct 16, 2012 at 10:21:02AM -0700, Junio C Hamano wrote:

> > I suppose we could do the way unpack-objects does: prefer present
> > objects and drop the new identical ones, no memcmp. Objects that are
> > not bases, or are ref-delta bases, can be safely dropped. ofs-delta
> > bases may lead to rewriting the pack. Do-able but not sure it's worth
> > the effort.
> 
> Until you read all the incoming pack data, you won't know what
> objects are used as bases for others, so unless you are keeping
> everything in core, you would have to spool the incoming data to a
> file and then rewrite the final pack file to "drop" these "can be
> safely dropped" objects, with or without offset delta encoding.

By definition, you know that you have another copy of these objects
(that is why you are dropping them). So you could treat later delta
references to them the same as thin-pack references, and re-add your
existing on-disk copy of the object to the end of the pack.

But still...the complexity is ugly, and we do not even have a measured
problem in the real world. This is not worth thinking about. :)

-Peff