Please be specific, tell us exactly what actions in Lightroom are running slowly.
Thanks for the response...
I'm beginning to suspect the issue is the disk that my catalogue is on. I might be seeing a hardware failures.
What I observe is that when I start Lightroom, the GUI displays, along with the list of folders (library view) down the left pane. But the folders don't show the number of photos in each entry. If I select a folder, Lightroom will eventually (a few minutes) show greyed out images in the grid view. If I walk away for 10 minutes or so, I might get thumbnails. I've never managed to wait long enough for a photo to fully load.
If I terminate Lightroom, a Lightroom process is left running. I cannot terminate this process through Task Manager, which implies that the process is stuck blocking on an OS operation. If I wait long enough (10-15 minutes) the process does eventually terminate.
All of this is consistent with disk problems. If I observe the contents of the disk through Windows Explorer, it will show me thumbnails, but it seems slow.
Anyway, I'm going to investigate the disk more thoroughly. If nobody else has seen a recent change in Lightroom behaviour, then that strikes me as the most likely cause.
I'm not sure what's going on, but I seem to have resolved it for the moment at least...
I have a full backup of my catalog on a second drive. Opening that catalog shows perfectly fine performance. So the problem isn't Lightroom itself. Since this catalog is a direct copy of the original, it shouldn't be a problem with the catalog, either. That supports the notion that the issue is with the drive that the original catalog is on.
But any performance tools I run on the original drive show it seems to behave normally.
Not sure where this leaves me as far as figuring out the source of the problem.
But, just experimenting, I blew away the previews folder on the original drive, and now Lightroom performs normally again.
So, there seems to have been something messed up in the previews folder that wasn't an issue in a copy of the folder. Severe fragmentation in the previews files? I would expect that to manifest slowly, while this problem showed up literally over night -- performed fine one day, terribly the next. So while I don't know what the root cause was, I'm back in business.