[MERGE] Re-order the packs during fetch

[Robert Collins]

On Sun, 2008-11-09 at 22:39 -0600, John Arbash Meinel wrote:
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> The attached patch changes the fetch logic slightly. After we have
> determined/transmitted the revisions, we know what pack files those
> revisions are in. Which means we also know what pack files the
> inventories and texts are in. The existing code keeps looking in all
> pack indexes for the inventories and texts.
> 
> This patch just changes it, so that after we read revisions, we sort the
> packs so that the interesting ones are put at the beginning of the list.
> 
> In my testing, this helps a lot when we are transmitting just a small
> amount of changes, that tend to be localized in certain packs. For
> example, updating my bzr.1.9 branch with 1 new revision. The new code
> still reads a lot of .rix info to find what revisions to transmit, but
> then reads very little .iix and .tix because everything is in the first
> pack it looks for.

I haven't read the code but this sounds like a good idea. 

I mentioned to you earlier a user that sees 400K of index reads, 70K of
pack reads to do a specific fetch; they were testing on a repo with only
one pack, so this won't help that case ;).

-Rob
-- 
GPG key available at: <http://www.robertcollins.net/keys.txt>.
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