Breaking up is hard to do
One common question about Lightroom is the maximum number of images for a single catalogue, and it’s usually the result of some slowdowns and asked with the expectation of needing more than one catalogue once you reach a magic number.
The trouble is, Lightroom is designed and optimized for being used as a single catalogue – eg you can only use one catalogue at a time and there are no cross-catalogue searching features. While it may offer features to support more than one catalogue, those features are designed for specific workflows such as moving work between computers, and you will hit a variety of problems and limitations if you use them to spread your workflow across a number of catalogues and fragment control of your pictures. You can certainly make Lightroom work that way, but it’s not making the best of it.
Slowdowns tend to be unrelated to the number of images in a catalogue and the only thing that is consistently slower is backing it up, and that isn’t a problem since it’s done after you’ve finished work. If you do experience a slowdown, you need to look elsewhere for a reason, so see Adobe’s notes on optimizing performance and troubleshooting performance. One option may be an “inbox” + master catalogue. New stuff will go into the inbox catalogue and you then periodically import it into the master and create a new inbox. But try running with one optimised catalogue and resolving the underlying problem. Above all, try optimising the large catalogue – that would be the first place to look.
While I recommend only using one catalogue (here, here, here and elsewhere), there are good reasons to use more than one and do so myself. In addition to my main catalogue which controls all my pictures, I also have another which controls a charity’s picture archive. I keep it completely separate – it catalogues only those pictures in a distinct set of folders which are never mixed with any others. I’ll also create temporary catalogues which might be for testing, demos, or working on the laptop. This is perfectly normal, and I’m not sure how you could use Lightroom otherwise, but it leaves no scope for confusion – my own workflow and pictures are controlled in a single Master Catalogue.lrcat.
Because it’s a difficult area, Peter Krogh of The DAM Book fame has released an ebook Multi-Catalog Workflow with Lightroom 5. It comes as a PDF supported by videos and covers a wide range of possibilities. I haven’t had the chance to read it in its entirety (been away and then absorbed in a DIY project), but I did like the idea of importing the videos into Lightroom so I could watch them in context. While others offer poor advice on using catalogues, Peter and I rarely disagree.