title: Coredata is very slow; swift
body: <p>i've made an iOS App tracking the gps route of the device.
  The problem is, that coredata needs very long to save, when i am tracking more than 5 min.
  I save an object called session and session have much location objects.
  the location object is [ [latitude, longitude] ]</p>
  
  <p>and the session object looks like [name: string, date: nsdate, average speed: double, high speed: double, driven kilometers: double, locations: [ [double, double] ] ]</p>
  
  <p>so... it works, but after 5 min. it takes i think 2 or 3 minutes to save</p>