There’s always speculation about how big a Lightroom catalog can be, but there’s nothing like the words of the Engineer that works on Catalogs in Lightroom about it. Earlier on LinkedIn, Lightroom Engineer Dan Tull had some words on the matter:
“There are definitely costs associated with larger catalogs. Various kinds of queries will slow down somewhat. However, probably the most significant cost of a large catalog is that the backup operation for it is monolithic (whole file) and thus proportional to the size of the catalog file. There are clever ways to use catalog exports to back up slices of the catalog (sets of photos) that are being actively modified without backing up the whole thing, but that’s a bit of an advanced technique.
The only hard limit I can think of off hand is that the LR catalog uses 4K pages and the version of SQLite LR is currently uses sets the maximum number of pages to 1024^3 – 1 which means (unless my math is off) a nearly 4 TB catalog is theoretically possible (yikes). Especially considering that the preview cache is usually much bigger than the catalog the size of your disk drive (or your patience) is likely to hit its limit before your catalog does.
The 4 TB figure doesn’t translate to any particular fixed maximum number of photos, based on the data I have available for per image catalog sizes, that’d translate to 200M photos in the catalog. If you use a lot of localized corrections and preserve the whole develop history, that count goes down significantly, though. “
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