What is "photoanalysisd" and why is it using 77% of my CPU?
Update for 2019, 16" MacBook Pro running Catalina 10.15.2:


start Photos, let it continue past the first dialogue box;
now Preferences in the app menu is clickable (it wasn't before);
Preferences > General , and untick both check boxes in Memories;
close Photos.


This stops photoanalysisd cold, no reboot or kill required.