Are you sure that's not including the previews folder?
I have 18,000 photos and the catalog (.lrcat) is 405 MB
My previews folder (.lrdata) is 6.7 GB, and I have standard sized previews.
My stats are as follows.
Files in my Catalog (mainly 99% raw files) 31,951.
Total file size of imported files 369.5 GB
Catalog.lrcat file size 569 MB
Catalog.lrcat.previews file size 44.7 GB (not many 1:1 previews)
Smart Previews. Zero.
If I am discarding previews after one week the previews should be decreasing. I see no change in previews.
I don't think you got Per's point. Are you looking at the size of the FOLDER which includes the catalog ???.lrcat and the previews folder?
You are correct. The catalog size is 857MB while the Previews are 20GB. So the message I get when I close LR that my catalog is over 4GB is not something I should be concerned with.
Still not sure why my previews are not decreasing in size since they should go away after 1 week.
The 4GB message is a bug, it is wrong, and so you will just need to click the box to ignore this message.
The previews that will be discarded after a week are the 1:1 previews.
Your 2048 px previews are regular previews, and will never be deleted, unless you delete the preview cache folder.
If you do that, Lightroom will recreate previews as needed - i.e. it will not create previews for a folder until you view that folder in the Library. So if you have folders that you rarely look at, there is a chance that it will take some time for your previews folder to grow to the size it had originally.
The downside is that the first time you browse any folder after deleting the preview cache, LR will take some time to recreate the previews.
The 4 GB message is a bug, and can be ignored.