I recently experienced very slow startup of my iMac and it seemed related to heavy Spotlight indexing. I researched this item on Google but I could not find a real Root cause.
I made a call to Apple support and I got the following suggestions:
- Goto to Finder
- Press Alt
- Goto Library
- Move folder Caches to the trash
- Move folder LaunchAgents to the trash
- Goto folder Preferences
- Move com.apple.spotlight.plist to the desktop
This resulted in my iMac performing as usual.
So it worked for me.
Be careful and make a backup before trying this fix.