How to disable Spotlight and mds_stores on Mac OS Catalina
In my experience, a failing disk and/or a disk filesystem that’s damaged or failing is the cause for most spotlight processes that run too long. Also, metadata importers that are added by programs like Office and others run to index their files and can cause issues.

Before you disable this entirely, have you opened the spotlight settings and added each user home folder to the privacy? This cleans all records of those user files from the database. Then you would restart the machine and perhaps boot to recovery HD and run Disk Utility to repair the disk.

Sometimes a clean install is all that’s needed - https://apple.stackexchange.com/a/66690/5472

Clearly, spotlight needs to take one pass over all the data, but then it should quit. As you say, if you don’t need it, adding the folders you wish to not have indexed is the easy way to let the system index things it needs, but ignore your user files, database files and other things that might cause temporary or permanent resource usage. I could see some high transaction data based never getting indexed if they don’t tell spotlight to not index files.


Preventing Spotlight from Indexing Files &amp; Folders?