The knowledge base has a partial answer only:
- If CPU usage is constantly dominated by Synology Universal Search-related processes, make sure the package has been updated to the latest version.
- If there are many files waiting to be indexed, you may pause the indexing and restart it during off-peak hours.
- If synoelasticd still uses too many resources after pausing indexing, check whether users are actively searching through Universal Search or File Station.
- For media indexing, go to Control Panel > Indexing Service > Media Indexing > Applications to see which packages are running media indexing.
- For conversion settings, go to Control Panel > Indexing Services > Conversion Setting, then tick Enable conversion by schedule to set a conversion schedule.
The knowledge base does not provide a direct fix specifically for Synology Photos indexing causing constant high CPU beyond these control options. It also notes that indexing/conversion can be paused to save resources.
Sources used: [8], [3]