Re: [PATCH 4/8] git-repack --max-pack-size: add fixup_header_footer()

From: Nicolas Pitre <nico@cam.org>
Date: Apr 9, 2007, 19:33 UTC
Message-ID: <alpine.LFD.0.98.0704091525260.28181@xanadu.home>
In-Reply-To: <56b7f5510704091211i3d101cafq371fbb96ca27238b@mail.gmail.com>

On Mon, 9 Apr 2007, Dana How wrote:

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> Wouldn't the following address the "object count unknown
> at the start of sequential pack writing" problem:
>  Write 0 for object count in the header. This is a flag to look for
>  another header of same format just before the final SHA-1 which
>  has the correct count. The SHA-1 is still a checksum of everything
>  before it and no seeking/rewriting is needed on generation.

No. You really wants to know up front how many objects a pack contains when streaming it. And this is not only for packs written to stdout.

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> Finally, when I generate several 2GB split packfiles,  I do notice
> the slight delay for fixup_header_footer(), and I do think it's a bit
> ugly, but in quantitative terms it's an insignificant part of a long
> operation that's infrequently performed.  Does this need to be
> optimized at all?

Maybe, maybe not. That depends how much data we think GIT could be used to manage in the future. With a 1TB pack file you definitely want to optimize that case.

OTOH this could wait for the real pack v4 too.

Nicolas