Re: Packfile can't be mapped

From: Nicolas Pitre <nico@cam.org>
Date: Aug 28, 2006, 04:27 UTC
Message-ID: <Pine.LNX.4.64.0608280014190.3683@localhost.localdomain>
In-Reply-To: <20060828024720.GD24204@spearce.org>

On Sun, 27 Aug 2006, Shawn Pearce wrote:

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> I'm going to try to get tree deltas written to the pack sometime this
> week. That should compact this intermediate pack down to something
> that git-pack-objects would be able to successfully mmap into a
> 32 bit address space.  A complete repack with no delta reuse will
> hopefully generate a pack closer to 400 MB in size.  But I know
> Jon would like to get that pack even smaller.  :)

One thing to consider in your code (if you didn't implement that already) is to _not_ attempt any delta on any object whose size is smaller than 50 bytes, and then limit the maximum delta size to object_size/2 - 20 (use that for the last argument to diff-delta() and store the undeltified object when diff-delta returns NULL). This way you'll avoid creating delta objects that are most likely to end up being _larger_ than the undeltified object.

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> I should point out that the input stream to fast-import was 20 GB
> (completely decompressed revisions from RCS) plus all commit data.
> The original CVS ,v files are around 3 GB.  An archive .tar.gz'ing
> the ,v files is around 550 MB.  Going to only 1.7 GB without tree
> or commit deltas is certainly pretty good.  :)

Good job indeed. Oh and you probably should not bother trying to deltify commit objects at all since that would be a waste of time.

Nicolas