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Re: initial thoughts on issue #3818: fix handling of externals in wc-ng

From: Stefan Sperling <stsp_at_elego.de>
Date: Wed, 23 Feb 2011 19:26:02 +0100

On Wed, Feb 23, 2011 at 04:26:52PM +0000, Julian Foad wrote:
> Hyrum K Wright wrote:
> > On Wed, Feb 23, 2011 at 9:53 AM, Julian Foad <julian.foad_at_wandisco.com> wrote:
> > > Stefan Sperling wrote:
> > >> So, ideally, we should decouple the
> > >> concept of a wcroot from the path. We could tie it to a wc_id instead.
> > >> This would allow us to use a single wc.db to manage several wcroots,
> > >> one for the parent working copy, and more for any externals within
> > >> this working copy.
> >
> > I've always thought we could handle it a different way: the externals
> > are just part of the same WC as the directories which contain them,
> > it's just the repos_id and/or repos_relpath which happen to point to a
> > disjoint location. In other words, externals are nothing more than
> > switched paths, save for the fact that their existence is communicable
> > to other clients via the properties (whereas "pure" switched paths are
> > single-client-only).
> >
> > Since all the plumbing for switched paths already exists, we should
> > just be able to reuse it for the externals cases. In fact, as
> > currently implemented, switch can do some *really* interesting things,
> > which Philip could probably better illuminate than me.
> >
> > In short, I don't think the answer is a set of wcroots but rather one
> > wcroot with a set of nodes (possibly pointing to various repos).
>
> +1 to that. In fact, I wrote about that idea a while back:
>
> Subject: [RFC] 'External' and 'Switched': common ground
> From: Julian Foad <julian.foad_at_wandisco.com>
> Date: Fri, 20 Aug 2010 18:54:09 +0100
> <http://svn.haxx.se/dev/archive-2010-08/0529.shtml>
>
> There are a few intentional differences in the way external directories
> (and files) behave, compared with switched nodes, but it looks far more
> sensible to implement them that way.

We need to preserve 1.6 semantics of how operations affect externals.
When treating externals just like switched paths, how will you make sure
that wc.db queries run within the context of one WC don't touch things
within an external WC?

Filtering on the wc_id makes this very easy.
Having to filter on a repos URL instead, how do you avoid filtering out
switched paths which are in fact part of the parent WC and not an external?

Or do you want to filter on the values of svn:externals within rows
returned by the query? Again, that is much harder than just filtering
on the wc_id, and requires parsing the properties to get at information
that might even been needed within SQL queries.

If we cannot easily tell the difference between a switched path
and an external, that is bad design, IMHO, and will lead to problems
down the road just like we had with file externals in 1.6.
Let's not repeat that mistake. Externals are special and need their own,
unique, representation in our design.
Received on 2011-02-23 19:26:39 CET

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