It would take a just a few lines of code to restore the ability of Import From Another Catalog to access catalogs stored on network filesystems (aka network drives or NAS).
Gory details:
LR catalogs are implemented using SQLite databases. Adobe changed the way LR 7 opens these databases, using SQLite's write-ahead logging (WAL) journal mode. WAL is significantly faster than the default journal mode used in LR 6 and earlier, but it doesn't work with databases (catalogs) residing on network filesystems. Thus, as a consequence of speeding up catalog access, Adobe also disabled the ability of Import From Another Catalog to read catalogs stored on network filesystems.
No one who knows has indicated whether this sacrifice of functionality in favor of catalog performance was thought through ahead of time or was an afterthought.
But there is a simple fix that allows both the use of WAL
and importing from catalogs on network filesystems. Normally, SQLite stores the WAL journal mode inside the database itself, and once stored in the database, there is no way for a program to open a database stored on a network filesystem to turn off the mode. But it's a very simple matter for LR to always keep the database in the default delete mode whenever the database is closed, putting it into WAL mode only when it is on a local disk and open.
Right after opening a database, LR would do:
if not pathIsOnNetworkVolume (catalog.path) then
do SQL command "pragma journal_mode=WAL"
This provides the desirable performance improvement if the catalog resides on a local disk, but still allows catalogs on network filesystems to be opened.
Right before closing the database on exit, LR would put the database back into default mode:
do SQL command "pragma journal_mode=DELETE"
With this, the Import From Another Catalog command would once again be able to import catalogs stored on network filesystems, as it has been doing in all versions prior to LR 7.
Now, some engineers with a little knowledge might object that the developers of SQLite warn against accessing SQLite databases over the network, due to deficiencies in
some implementations of network file locking. In general, that's a complicated subject as it applies to LR. But for importing from a network catalog, it's a non-issue, since the SQLite warning only applies to writing network databases, while the Import From Another Catalog command only reads the databases.
I tested the feasibility of this solution with MacOS LR 7.3.1, using SQLite to remove to remove the WAL journal mode from a catalog, and LR was able to successfully import from it, just like LR 6.
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