[MERGE][1.8?] Make 'bzr co' more memory sensitive

[John Arbash Meinel]

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Vincent Ladeuil wrote:
>>>>>> "john" == John Arbash Meinel <john at arbash-meinel.com> writes:
> 
>     john> Vincent Ladeuil wrote:
>     john> ...
> 
>     john> +        """For the given keys, split them up based on their prefix.
>     john> +
>     john> +        To keep memory pressure somewhat under control, split the
>     john> +        requests back into per-file-id requests, otherwise "bzr co"
>     john> +        extracts the full tree into memory before writing it to disk.
>     john> +        This should be revisited if _get_content_maps() can ever cross
>     john> +        file-id boundaries.
>     >> 
>     >> Can you write a test guarding from regression on that particular
>     >> case ?
>     >> 
>     >> BB:tweak
>     >> 
>     >> Convert that to approve from me if the test above is really too
>     >> hard to get right, but in that case, add a FIXME.
> 
>     john> I don't really know how to write a correct test (that
>     john> maximum memory is constrained).
> 
> I meant regression on "_get_content_maps() can ever cross file-id
> boundaries.".
> 
>         Vincent
> 

I honestly don't know how we would do it. Because I don't know how we
would end up implementing cross-file-id storage, and thus how to
*trigger* that in real life.

If that is your only request, then I can submit the patch as is. (Note
that I did work out a patch which adds an explicit test case, I just
don't like it because it needs 100MB of ram and disk space, and takes
60s to finish.)

John
=:->
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