What is "photoanalysisd" and why is it using 77% of my CPU?
Your iMac is currently processing the photos in your Photos library, presumably because you’ve just imported/converted an existing Photos library from an earlier version of macOS.
If you suspect this has been the cause of your sluggishness for a couple of days, then it’s most likely you’ve got a very large photo library and that it’s being processed for the first time on your new iMac.
The fact that Photos isn’t running actually fits with your scenario, as launching the Photos app will pause the photoanalysisd daemon.
Although it takes a long time, once it’s finished your Photos app will be able to perform a lot of advanced functions due to all the metadata etc it’s processed, so I would let it finish what it’s doing.
NOTE:
Should you need to pause the process in order to free up some of your CPU, I would recommend just opening the Photos app for a while and then quitting it when you’re not using the computer. Note, however, that minimising the Photos app will act to restart the photoanalysisd daemon, so just leave it running in the background while you want to keep the daemon paused.
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 main app menu under Photos just right after Apple logo is clickable (it wasn't before);
-
Preferences… (⌘+,) → General tab , and untick both check boxes in Memories;
-
close Photos.
This stops photoanalysisd cold, no reboot or kill required.
After photoanalysisd had been taking up 3 cores for over a month, I found a solution that reduced the CPU usage dramatically for me on High Sierra. I went into Photos and added names to some pictures - 4 pictures in total using 3 names. Photoanalysisd is currently using 0% whether or not Photos is open.
I have only a dozen or so photos in my library (this is my spare computer, my photos are on my main computer) and I've let the process run for a week, and it is still eating up 100% of both cores. My machine is unresponsive with the CPU fan at 100% (13" MacBook Pro Mid-2010). None of the solutions I found on the web worked, I finally temporarily renamed my photo library to hide it from the deamon, and instantly had both CPUs go from 100% to around 5%.