Whenever I log into my MacBook Pro the CPU cranks up to 100%+ for a few seconds, my board gets hot, and the fans start going. I open up Activity Monitor to find that the culprit is 'photolibraryd'. What's going on? What's it doing that uses so much CPU?
In my case photolibraryd wants to conntect to edge.quantserve.com on Port 80 (http), probably to set a tracker-cookie or web-beacon. I stopped this behaviour with Little Snitch.
For more information on quantserve, read this guardian-article: https://www.theguardian.com/technology/2012/apr/23/quantcast-tracking-trackers-cookies-web-monitoring
If Photo Stream is enabled, photolibraryd connects to iCloud and checks for any new photos in your Photo Stream. If there are new photos, they are downloaded and added to the photo library you have selected as your ‘system’ library.
It also matches photos that are on your local library and in iCloud. So for instance, if you have a sync problem, you can toggle iCloud Photo Library in
Photos app → Preferences → iCloud and this will cause a complete re-sync of the local and the iCloud photos.
When this happens (at least on my 51K photo library), it takes 24 hours or so of photolibraryd running to match photos and sync the changes.