Core Data inserting and saving slow - ios

Question

I'm parsing data from a JSON file that has approximately 20000 objects. I've been running the time profiler to figure out where my bottlenecks are and speed up the parse and I've managed to reduce the parse time by 45%, however according to the time profiler 78% of my time is being taken by the context.save() and much of the heavy portions throughout the parse are sourcing from where I call NSEntityDescription.insertNewObjectForEntityForName.
Does anyone have any idea if theres any way to speed this up? I'm currently batching my saves every 5000 objects. I tried groupings of 100,1000,2000,5000,10000 and I found that 5000 was the most optimal on the device I'm running. I've read through the Core Data Programming Guide but have found most of the advice it gives is to optimizing fetching on large numbers of data and not parsing or inserting.
The answer could very well be, Core Data has its limitations, but I wanted to know if anyone has found ways to further optimize inserting thousands of objects.
UPDATE
As requested some sample code on how I handle parsing
class func parseCategories(data: NSDictionary, context: NSManagedObjectContext, completion: ((success: Bool) -> Void)) {
let totalCategories = data.allValues.count
var categoriesParsed = 0
for (index, category) in data.allValues.enumerate() {
let privateContext = NSManagedObjectContext(concurrencyType: NSManagedObjectContextConcurrencyType.PrivateQueueConcurrencyType)
privateContext.persistentStoreCoordinator = (UIApplication.sharedApplication().delegate as! AppDelegate).persistentStoreCoordinator!
privateContext.mergePolicy = NSMergeByPropertyStoreTrumpMergePolicy
//Do the parsing for this iteration on a separate background thread
privateContext.performBlock({ () -> Void in
guard let categoryData = category.valueForKey("category") as? NSArray else{
print("Fatal Error: could not parse the category data into an NSArray. This should never happen")
completion(success: false)
return
}
let newCategory: Categories?
do {
let newCategory = NSEntityDescription.insertNewObjectForEntityForName("Categories", inManagedObjectContext: privateContext) as! Categories
newCategory.name = category.valueForKey("name") as? String ?? ""
newCategory.sortOrder = category.valueForKey("sortOrder") as? NSNumber ?? -1
SubCategory.parseSubcategories(category.valueForKey("subcategories") as! NSArray, parentCategory: newCategory, context: privateContext)
} catch {
print("Could not create the Category object as expected \(error)")
completion(success: false)
}
do {
print("Num Objects Inserted: \(privateContext.insertedObjects.count)") //Num is between 3-5k
try privateContext.save()
} catch {
completion(success: false)
return
}
categoriesParsed+=1
if categoriesParsed == totalCategories{
completion(success: true)
}
})
}
}
In the above code, I look through the top level data objects which I call a "Category", I spin off background threads for each object to parse concurrently. There are only 3 of this top level object, so it doesn't get too thread heavy.
Each Category has SubCategories, and several other levels of child objects which yield several thousand objects each getting inserted.
My core data stack is configured with one sqlite database the standard way that is configured when you create an app with CoreData

Answer 1

One reason is that you're saving the managed object context in each single iteration, which is expensive and not needed. Save it after the last item has been inserted.