NSFetchRequest memory problems

Question

I've posted similar questions about different things relating to this, but have been struggling with this for about a week now, to no avail. It all comes down to this code:

NSFetchRequest *oldFetchRequest = [[NSFetchRequest alloc] init];
        NSEntityDescription *oldEntryEntity = [NSEntityDescription entityForName:@"Media"
                                                          inManagedObjectContext:oldContext];
        [oldFetchRequest setEntity:oldEntryEntity];
        [oldFetchRequest setFetchBatchSize:10];
        NSArray *medias = [oldContext executeFetchRequest:oldFetchRequest error:&error];

    int i = 0;

    int count = [oldContext countForFetchRequest:oldFetchRequest error:nil];

    NSLog(@"count: %i", count);

    while (i < count) {
        @autoreleasepool {
        NSManagedObject *media = [medias objectAtIndex:i];

            [oldContext refreshObject:media mergeChanges:NO];

        NSLog(@"i: %i", i);
        i++;
        }
    }

Count should be reaching about 250, the amount of media items. It actually reaches about 100 before the app runs out of memory and crashes. It builds up more and more memory every time this code is run, presumably as each media contains a number of NSData attributes, including a large one. Instruments shows memory increasing every time the code is run.

@autoreleasepool and refreshObject:mergeChanges: I added to try and fix this problem, but they haven't worked.

What i'm trying to do is move all of the items from this store into a new one manually, as standard migration doesn't work with large data. This is the starting point.

is your code crashing without migrating? As is in this listing? — NeverBe, Sep 24 '12 at 22:22
Yes, migration code is all taken out. All the code we're left with is the code above. I haven't commented any code out or hidden any. — Andrew, Sep 24 '12 at 22:28
http://stackoverflow.com/questions/12295415/core-data-memory-usage-and-memory-warning See LombaX solutions, may be it help — NeverBe, Sep 24 '12 at 22:39
This worked, but at the next line i'd put in, `[media valueForKey:@"originalImage"];` it crashes. — Andrew, Sep 25 '12 at 00:06

score 1 · Answer 1 · answered Sep 25 '12 at 16:09

For each media you are allocating a new instance of NSManagedObject. Instead, you could define one instance of media and reuse that.

Also, I believe that you could actually use a NSFetchedResultsController which is optimized for iterating through a set of fetch results and has all kinds of behind the scenes memory optimizations.

You could then simply iterate like this:

for (id object in _fetchedResultsController.fetchedObjects)

I think both these suggestions should reduce the memory footprint significantly.

I've tried doing it with NSFetchedResultsController, to the same result. Any additional techniques I could try in relation to NSFetchedResultsController to keep the memory from increasing? — Andrew, Sep 27 '12 at 19:30

NSFetchRequest memory problems

1 Answers1