I’ve been having recent problems with spotlight’s mds process taking up a lot of cpu. In searching I found this:

… and I discovered the main culprit: Backblaze (cloud backup) was generating file lists whenever anything was change don the system, and mds was indexing them.

Sure enough that was the problem. So, if you are using Backblaze you should probably add it to the System Preferences -> Spotlight -> Privacy list.