How to best move a huge .sqlite database to a new directory on an old, low memory iOS device?

Question

For my latest app update, I have to move the user's Core Data .sqlite database from the Documents directory to the Application Support directory. I use the migratePersistentStore:toURL:options:withType:error: method. I am dealing with one user who somehow managed to save enough data in her database so that it is now a whopping 9G. On top of that, her device is an iPad Air 1 - which had memory issues around the time it came out five or six years ago, and now it is 2018 and she is running the latest iOS. The migratePersistentStore:toURL:options:withType:error: method keeps crashing the app with low memory. But I have no other way to get the .sqlite to the necessary location. Can anyone advise me on how to best approach this situation? Ideally, something I could do in my code - but I would even appreciate suggestions on other ways I could just help the user to manually move that massive database at this point!

Answer 1

I guess you use migratePersistentStore because its the official way to do it. Its a good way, but sometimes you have to make your hands dirty:

Manually-moving database at app-start before you load it

This post shows that CoreData may use more than one file which you have to move. You can list the files in the directory, use a regex find all the files which have to be moved, move them to the new location and then load CoreData as usual from the new location.

This however requires there to be the necessary infrastructure in place to do this. You‘ll figure it out if you want to go this path.

You can hide this behind a feature-flag, only with a code, only for a certain user or after crashing with low memory so it doesn‘t impact users who don‘t need it.