Be more clever when triggering diff calculations. If a diff calc is started bring it to its end. Before starting look if it is done and in db notice it as ready. When a calculation is on its way add to list of waiting calls to avoid starting a calculation again. Only do two diff calcs at a time.

teichmann@intevation.de = sascha.teichmann@intevation.de
bernhard.reiter@intevation.de = bernhard@intevation.de