Core Data delay when switching NSPersistentStore files

I'm developing an app with Core Data that periodically downloads all the data from a webservice. Since the download can fail or be cancelled by the user, I want to be able to roll back to the previous state. I tried undoing the NSManagedObjectContext, but that seemed a bit slow (I have tens of thousands of entities). What I'm doing right now is making a backup of the persistent store file, download the data, and, if the download fails, replace the store file 开发者_高级运维with the backup. This seems to work correctly, except there seems to be a delay after I can fetch entities from the store: if after the download I go immediately to a UITableView that uses an NSFetchedResultsController, I find it empty. If I wait some seconds, everything is ok.

So my question is: has anyone had this kind of delays too? Is there something that can be done to avoid this problem, something that forces everything to be ready, even if it blocks the thread?

I haven't used this setup but I think the delay you are seeing is probably caused by Core Data having to clear all it's caching. Core Data uses If you use a cache with the fetched results controller it will have to test and then delete it's existing cache.

I think the best thing to do is to tear down you Core Data stack and reboot it from scratch. That includes recreating a fresh fetched results controller.