Re: Merge-friendly text-based data storage

From: Junio C Hamano <gitster@pobox.com>
Date: Mar 27, 2012, 15:21 UTC
Message-ID: <7vzkb2jchu.fsf@alter.siamese.dyndns.org>
In-Reply-To: <CAD77+gR=p+jhN5qNoRgjtQPHqgqrdtcSmqAy_4d0NUaqE6ZkVg@mail.gmail.com>

Richard Hartmann <richih.mailinglist@gmail.com> writes:

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> On Tue, Mar 27, 2012 at 11:12, Holger Hellmuth <hellmuth@ira.uka.de> wrote:
>
>> I may be misunderstanding something, but lets assume you want to merge a
>> file that has "version: 0" with one that has "version: 1" and their last
>> common ancestor would have "version: 0" naturally. So the merge would not
>> fail even though the file layout changes.
>
> Ugh, I did not consider that. I can't come up with a way, other than a
> custom merge driver, to prevent this. Am I correct?

You are the only judge to that statement: "I can't come up with...".

I can't either, but I know a custom ll-merge driver would work. It is designed for this kind of thing. It will know both version 0 and version 1 format, read from each and writes out the merged result in whatever format it wants to use.

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>> the only way
>> would be to store each data line in its own file. As you store file paths
>> that would even fit, but I doubt it is what you had in mind
>
> I considered this as well, but that's extremely expensive and wasteful.

And it does not solve anything. The "version" file may cleanly merge to a new version, and there is no way for the merge result of "version" file to affect the outcome of merges in other files.