My PIctures Directory have 460GB of Images (~35k Files) and after digikam detected/importat all them i wanted to re-create all thumbnails for faster viewing.

Here seems a memory leek to exist.

I used Tools --> Maintenance to re-create all thumbnails and said use all processor cores

From that its hard to tell what hes doing, memory usage increases but CPU Usage stays down, so it seems he tries to load all images into memory before doing anything.

As soon digikam process reached 15,5 GB memory usage, my system freezes for about 20 Seconds and then the Linux Kernel kills digikam.

Yeah thats all what i can say, im not able to recreate all thumbnails as digikam wants to use more than 16GB memory for this action (what my system does not have)

Reproducible: Always

Steps to Reproduce:
Try to re-create all thumbnails of a large collection
Actual Results:  
digiKam crashed (because it gets killed by the kernel)

Expected Results:  
obvious