Catalogs (catalogues) in Lightroom Classic
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One of the greatest strengths of Lightroom Classic is that its edits are none destructive and that the original images are not changed in the application. Instead the edits are stored inside Lightroom Classic in the catalog and applied at time of editing and only baked in when exported to an alternative file format, commonly JPG or TIF.
The catalog holds not only the edit recipes, but the physical location of the actual images, keywords, collection membership and other metadata. While the database is now old and far from optimal, it works well, if not particularly fast and has served users well.
Lightroom Classic supports the capability of creating, using and saving multiple catalogs, but only one at a time. The catalog model also necessitates the creation of a number of catalog supporting files, one example being the file holding previews of the edited image. All of these files are kept in the same directory / folder as the catalog file itself which ends in .lrcat and all are required for successful catalog usage.
The vast majority of Lightroom Classic users are best served by a single catalog. Back in the very early days of Lightroom Classic, some folks recommended multiple catalogs, more out of concern for database performance than any other reason. Professionals who contract to multiple clients may choose to have separate catalogs for each client. I do this myself, but it does create risk should the user not be paying attention to which catalog is being used at what time.
Lightroom Classic does not allow for more than one catalog to be open at one time, and does not allow for the same catalog to be opened on more than one computer at the same time. I hope that all Lightroom Classic users know this, but as Adobe is focused on cloud everything, it looks to many of us that Lightroom Classic has become the bastard stepchild. Recent bugs in releases demonstrate that Adobe has not maintained their quality commitment to Lightroom Classic.
The risk of multiple catalogs is that if you are not aware of which catalog is in use, you may import images, do edits, and perform other functions and then find after the fact that all your work is in the “wrong” catalog. Lightroom Classic does provide a function to import from one catalog to another and while it does work, the user does need to have a deep understanding of the Lightroom Classic infrastructure to make this successful.
Which brings me to my point. If you prefer to use Lightroom Classic, as I do and as do most professionals, instead of the cloud version, stick to one catalog only. Use collections (not folders) to segregate and manage your images. While the database structure is now ancient, a catalog with a million images is quite viable, I know from personal experience.
As noted you can have more than one catalog with Lightroom Classic. The pertinent question to ask before doing so is to identify the whys and benefits of making your life more complicated.
