Multiple Photos Libraries - I'm favouring multiple

Many of us use multiple Libraries to help keep things straight. We have archival Libraries that may not change much, and a Favorites Library that is synced through iCloud with our other devices. I have a Library for work stuff, one for my parents' families, and one for my wife's parents' families. (I kept getting confused and couldn't remember who people belonged to when they were all together.) I have several others, as well.

Having too many pictures in a Library slows down searches, face IDs, Duplicate finding, and all that kind of background curation stuff. It's best to keep a Library under 40K pictures if you can.

We use the 3rd party app  PowerPhotos ($30) to help keep track of multiple libraries and to make it easier to switch among them.

The thread you linked is pretty old.

The discussion you are citing is rather old. At that time the current system has been High Sierra, and Photos has changed a lot since then.

The Photos.app is now much more ambitious and is doing a lot of background processing, scanning the library and analysing it with artificial intelligence. The size of the library matters now a lot more than several years ago.

It helps to keep the library small, but try to keep related photos, that you will need to use together, in one library.

My Photos Library is currently having a size of 360GB, with 67000 photos and 564 videos.

Photos is still sufficiently responsive when I am working with it, but after each major system upgrade Photos will be slow for a long time, while the library needs to be upgraded to the new system version and scanned again. This has been different in the older versions of Photos, that did not need to analyse the library for objects and scenes.

Some parts of the user interface are also not up to dealing with a very large library. The list of keywords is a flat list, that should be kept short, or it will take a long time to select a keyword, when defining smart albums based on keywords. The People and Pets album is also a flat album, and difficult to manage with more than atousand people in it.

When designing our libraries we should find a way to have all essential photos in our system photos library, because only the system Photos Library can sync with iCloud and is visible in the Media Browser for other applications, but archive photos, that are not necessary in the system photos library in additional archive libraries.

You're welcome, andynick. 😊