[PATCH 00 of 10] RFC: Light-Weight Copy

TK Soh teekaysoh at gmail.com
Sun Sep 12 19:52:21 CDT 2010

On Thu, Sep 9, 2010 at 3:48 AM, Sune Foldager <cryo at cyanite.org> wrote:
> NOTE: This queue is not push-ready. It's posted for initial comments and feedback.

Is there some place I can go to download these patches? Kinda clumsy
to save the patches using gmail.

> This patch queue implements light-weight copy in Mercurial. Light-weight copy prevents hg
> from storing a complete version of a file when it's copied or renamed. It's a change in
> the storage format; the API stays the same.
> The patch queue was originally created by Vsevolod Solovyov, and has been worked on by me
> subsequently. The code is essentially the same, although there has been a number of
> changes, bug fixes, patch folding and optimizations. The final patch of the queue, is
> recent work by me.
> Currently, all patches are attributed to me; I don't consider the queue to be push-ready,
> so this is not necessarily finalized either. See below.
> The queue applies towards 5b849148b620, which is close to crew-default-tip. It likely
> applies against tip as well.
> I'll briefly describe how light-weight copy ("lwcopy") is implemented here:
> Whenever a copy-revision is stored in the filelog, lwcopy stores, instead of the whole
> file text, only a delta between the previous filelog (for the old file name). Often, this
> delta will be empty. A flag is added to metadata to signal that this has been done. This
> allows lwcopy-changesets and old-style changesets to coexist in the same repository.
> The hash values are calculated against the full text, as before, so nothing changes in a
> repository, even if it's converted to lwcopy.
> To control these things, a few methods in revlog have been split into public and private
> parts, which filelog can then override.
> Since the changes are at a pretty low level, generally private methods, the wire protocol
> never sees any changes, and old-style changegroups are simply emulated: when reading
> changegroups, lwcopy changesets are expanded to the full text; when adding changegroups,
> copy changesets are lwcopy-fied automatically.
> The exception is stream-clone, which sends the store files directly. The last patch in the
> queue addresses this by introducing a new stream-capability the client can use to decide
> whether or not it understands the streaming format. If it doesn't, it'll use pull-clone.
> Notes on the state of the queue:
> The number of, and division of the patches are largely as Vsevolod left them. It may make
> sense to reorder and/or fold some of them, and certainly to flesh out the commit messages.
> Also, no tests are added, but the queue does fix a few tests which fail due to changed
> sizes of the filelogs (ironically, due to the small data sizes generally employed in
> examples, the sizes are larger than before; this is due to the new 'lwcopy' metadata
> element). The test suite passes.
> Note that the suite doesn't test old client vs. new server or vice-versa. I have done
> manual testing of various scenarios with success. This includes cloning a lwcopy repo with
> an old client, making a new copy or rename and pushing the change back, etc. All this
> works as expected.
> Apart from the above, the patches are pretty much finished, as I see it. I would like to
> make some minor changes, e.g. rename the 'lwcopy' metadata to 'copylw' to align with the
> other two copy-related keys, maybe rename a few methods and similar.
> Comments, questions and suggestions are welcome.
> --
> Sune Foldager
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