We have several product lines built around a common core and currently maintain them in SVN using externals. Moving to mercurial, it is natural to move to use hg sub-repositories.
The thing is the core is quite large (probably >GB, judging by the SVN repo), and a typical developer sometimes wishes to work simultaneously on several products, say 3-4.
Did I get it correctly that it usually means a developer would have the core replicated 3-4 times for each developer, with its entire history?
Also, if a developer wishes to perform some simple operation in another product, it would mean the core have to be pulled first, even though it is already available at the client (several time…)?
In order to truly share the subrepository (and not its working copy), you can use the share extension. However, that makes the cloning process a bit counter-intuitive:
And so on. But I warn you that you are going to have more than one headache with this setup. At work, we have a similar setup, but instead the shared subrepository has a branch (not a named branch, but a clone branch, a dedicated master repository) for each project that uses it. That way projects can modify the shared code independently while still having the easy merging between them.