iOS - CoreData deleting objects doesn't free disk space

Question

I am deleting CoreData objects using this method:

    NSManagedObjectContext *theContext = [self managedObjectContext];
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:nameEntity];
[fetchRequest setIncludesPropertyValues:NO]; //only fetch the managedObjectID
[fetchRequest setPredicate:predicate];
NSError *error;
NSArray *fetchedObjects = [theContext executeFetchRequest:fetchRequest error:&error];
for (NSManagedObject *object in fetchedObjects)
{
    [theContext deleteObject:object];
}

error = nil;
if(![theContext save:&error]){
    NSLog(@"Couldn't save: %@", error);
}

What I don't understand is that for instance I download data and store it, and in the Settings I can see that my app uses 5MB of disk space. Once I delete the data using this method, it says my app uses 6.3MB of data. That makes absolutely no sense at all. What am I doing wrong? Why isn't the data being deleted correctly?

Answer 1

When using the sqlite store, the storage is managed by sqlite, not the core data framework itself. When you delete a managed object, the row is deleted from the appropriate table. In a typical database, this does not result in freeing any disk space. As for why the space used might actually increase, this speculation on my part, but I think it's because of the transaction logging. Even though the transaction is complete, the log is not immediately purged.

I would recommend that you not worry about this. The sqlite library will have internal management to compact tables (reclaim space from deleted rows) and purge old transaction records.

Answer 2

You can open the core data store with the SQLite vacuum option set to reclaim disk space. Eg

NSDictionary *storeOptionsDict=@{NSSQLiteManualVacuumOption : @YES};
[persistentStoreCoordinator addPersistentStoreWithType: NSSQLiteStoreType configuration: nil URL: sourceStoreURL options: storeOptionsDict error: &error];

See this older question: How to VACUUM a Core Data SQLite db?