countForFetchRequest seems to bog down on really big collections of
entities. For approx 170K entities it takes around 10 seconds on an iPhone
3GS to count them, which is a problem in a UITableView where you are trying
to display a list of entities and associated counts.
A GCD based solution, that queues up countForFetchRequest on a concurrent
queue for each entity, and then updates the corresponding cell when
finished, seems to work pretty well, although one or two big entity counts
essentially bog down all the requests behind them. Counts are cached so
that countForFetchRequest is only called once for any entity.
Code below, can anyone suggest any further optimization or different
approaches that might be more effective?
(I'm aware of the danger of multi-threading core data - this particular
managed object context never changes and nothing is happening to it on other
threads when this read is going on)
- (void) countEntitiesNamed:(NSString *)entityName
inContext:(NSManagedObjectContext *)context forIndexPath:(NSIndexPath
*)indexPath {
NSNumber *rowCountObject = [self.rowCountMD valueForKey:entityName];
if (rowCountObject) return;
//
http://www.mikeash.com/pyblog/friday-qa-2009-08-28-intro-to-grand-central-dispatch-part-i-basics-and-dispatch-queues.html
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,
0), ^{
NSEntityDescription *ed;
NSFetchRequest *frq;
frq = [[[NSFetchRequest alloc] init] autorelease];
ed = [NSEntityDescription entityForName:entityName
inManagedObjectContext:context];
[frq setEntity:ed];
NSDate *startDate = [NSDate date];
NSUInteger rowCount = [context countForFetchRequest:frq error:nil];
NSTimeInterval timeInterval = -[startDate timeIntervalSinceNow];
DLog(@"%0.2lf seconds for %d %@ ",timeInterval,rowCount,entityName);
dispatch_async(dispatch_get_main_queue(), ^{
[rowCountMD setValue:[NSNumber numberWithInteger:rowCount]
forKey:entityName];
UITableViewCell *cell = [self.tableView cellForRowAtIndexPath:indexPath];
cell.detailTextLabel.text = [NSString stringWithFormat:@"%@ objects",
[NSNumberFormatter localizedStringFromNumber:[NSNumber
numberWithInteger:rowCount]
numberStyle:NSNumberFormatterDecimalStyle]];
});
});
}
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