When servicing a large pics collection, running alle servicing roptions takes time  and time (in my case several days). 

Reffering on single pics, users are _not_ able to see "from outside" the status of each pic, concerning availability, preview (thumbnails), face-recognition status and so on.  


Reproducible: Always

Steps to Reproduce:
1. it is an implicite issues, no error 
2.
3.


Expected Results:  
I suggest strongly: mark every servicing option for very pic.

Given this situation, digiKam would be able to decide if a pic contains already that treatment (as building a thumbnail, or face recognition, e.g.).

Key topic should be, to run every time-consuming option once per pic. 

Therefore, digiKam needs to "decide" which pic need a time-consuming treatment or not. 

Besides, this could affect/support an incorporating-of-a-database-on-demand- feature. Thereby, I mean, that all the data produced in servicing progress, would be available instanteously when incorporating a database (path containing a pic collection) or get switched off in the contradictous situation.

This is not an error or failure rather than a fundamentel limitation. For this reason, I consider this as a "major fault"