wc-to-wc copies and wc-ng

The wc-ng approach is a database transaction that modifies the
database and adds one or more workqueue items to modify the working
files and directories. At least initially, there is likely to be one
transaction per versioned node in the source. I suppose when we
centralise it might be possible to copy the whole tree in a single
transaction, but I'm not sure what the workqueue would look like.

I'm not sure how/when unversioned items get handled. Do we create
workqueue items for them when adding the parent directory? Does each
one get its own transaction/workqueue? Do we copy them without
transactions?

One of the problems before centralisation is that a copied directory
cannot be fully added to the database until the directory has been
created in the filesystem. We can add the directory to the database
in the parent and we can put workqueue items there as well, but a
directory also needs to be added to its own database.

I suppose we could create the new directory before executing the
transaction, but that seems to be completely at odds with the
transaction/workqueue approach. It's probably better to have the
transaction just add the directory in the parent database and have
workqueue items that create the new directory that modify the new
database.

Is the current svn_wc__db_op_copy_file iterface the correct one for
wc-to-wc copies? It's sensible for a repo-to-wc copy where all the
source information has to be inserted into the database, but for a
wc-to-wc copy that information is in the database already. Perhaps we
should just pass the source path and copy all the information with a
database query?

Perhaps we should continue to do a dumb copy as the first step even
with wc-ng? That would create a new completely unversioned tree and
then one or more tranactions could modify the database(s). At the
moment there is no way to restart an interrupted copy, so although the
transaction/workqueue approach means that the nodes will show up as
incomplete it's not clear what the user could do.

-- 
Philip