[Klojum]

But if you think this thread is inappropriate, just delete it and I zip it.

I never said any of that, I simply asked for a log file...
All because we have no crystal ball here, and any details still can be useful.

big databases means

Details mean things like which database server, which database server version. We want to do those affords you talk about.
Things do not work by magic. Only a week ago we had to implement a bug fix for older MySQL databases.

Trying to play a song from a couple thousands selection takes minutes.

Sure... so who needs a log file, right? For all I know you installed Kodi on an ancient HAM radio.
Sorry, but general yammering without actually giving us information as requested isn't helping us.

I think this is completely legacy, but maybe it helps tracing...

Not for me.