Tutorial :Core Data client+server/background saving/general import question


I'm working on a Core Data-based application that has a Mac application acting as a 'server' and an iPhone as a client. Everything is going swimmingly, except I'm running into performance issues.

When the user taps an object, the server must return some objects related to that object (nothing too heavy, usually 3-4 objects) and show a UI to choose some options. This needs to be as fast as possible. The round-trip time to the server, the server pulling the data, formatting it, returning it to the client, and the client creating NSManagedObjects from the data (which cannot be optimized further) is about 200 ms. The code relating to presenting the UI (which cannot be optimized further, again) requires around 150 ms. On an iPod touch 2G running iOS 4.0, the single line of code saving the managed object context after the objects are imported is taking anywhere from 150-200 ms.

To me, this screams that I should be backgrounding the managed object context saving. However, as far as I understand it, that won't really meet my needs. If I want to save the managed object context on a background thread, then all the objects in it must have been created on a background thread in a separate managed object context, so I won't see any speed gain because it will still take 100-200 ms for the save to occur, and I'll be seeing even more overhead because I'll still need to tell my main thread to update it's managed objects from the backgrounded managed object context's save before my view controller sees that it needs to refresh itself.

Am I missing an obvious solution? Is there something about Core Data I could use in this situation that would help? I hate to throw such a general question like this out there, but I'm at a complete loss where to go from here.


Sounds like you need to move the entire server communication to a background thread. If you did that then the entire UI would be responsive no matter how long the communication with the server took.

To do this, you stand up a second NSManagedObjectContext on the background thread connected to the same NSPersistentStoreCoordinator. Then you perform your server communication on that background thread (it might even make sense to use an NSOperation) and save the changes.

Your main thread and therefore main NSManagedObjectContext listens for save notifications and when it receives one it updates the main thread and UI. This will eliminate any freezing you are seeing and the processing time becomes mostly irrelevant.

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