CoreData: NSFetchedResultsController performances

[J0ker]

Hi!

In the model, I have two entities: Record and Category. Category is one-to-many with Record through inverse relationship. The persistent store is of SQLITE type and the db is not so small, about 23MB (17k records).

I use a list-detail design to show the records table and the detailed record view.The list viewController uses NSFetchedResultsController.

Building on the device, if I don't use setFetchBatchSize:

CoreData: annotation: sql connection fetch time: 15.8800s
CoreData: annotation: total fetch execution time: 16.9198s for 17028 rows.

OMG!

If I use setFetchBatchSize:25, everything works great again:

CoreData: annotation: sql connection fetch time: 1.1736s
CoreData: annotation: total fetch execution time: 1.1900s for 17028 rows.

Yeah, that would be great! But it is not! In the list viewController, when user taps on a record I allocate a detailed viewController and I pass the record at the indexPath in the fetchedResultsController:

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
Record *record = (Record *)[fetchedResultsController objectAtIndexPath:indexPath];
RecordViewController *recordViewController= [[RecordViewController alloc] init];
    recordViewController.record = record;
    [self.navigationController pushViewController:recordViewController animated:YES];
    [recordViewController release];
}

NOW, in the detailed viewController, I have a button to set a record as favorite or not:

- (IBAction) setFavorite {
if (![record.ISFAV intValue]) 
[record setValue:[NSNumber numberWithInt:1] forKey:@"ISFAV"];
	
else 
[record setValue:[NSNumber numberWithInt:0] forKey:@"ISFAV"];

###SAVE ON THE CONTEXT HERE###

}

OK, are u ready? If I tap on the first record in the list, then I add or remove it from the favorites, it happens in 0.0046 seconds, instantly! Console with SQL Debug mode shows only the UPDATE statement:

CoreData: sql: BEGIN EXCLUSIVE
CoreData: sql: UPDATE ZRECORD SET ZISFAV = ?, Z_OPT = ? WHERE Z_PK = ? AND Z_OPT = ?
CoreData: sql: COMMIT
CoreData: annotation: sql execution time: 0.0046s

If I scroll very fast the big list (and I obviously find the batch requests on the console), when I tap a record reached with many batch requests and I add\remove it from favorites, many many many many (too many! the more I scroll the more they are!) SELECT statements appears in the console before the UPDATE one. This means total execution time not acceptable (the uibutton freezes for a long time on the iphone).

What's happening? The problem is clearly related to the batched fetch requests. More fetch requests = more SELECT statements before the UPDATE statement. This is one of them:

CoreData: sql: SELECT 0, t0.Z_PK, t0.Z_OPT, t0.ZCONTENT, t0.ZCONTENT2, t0.ZISUSER, t0.ZISFAV, t0.ZTITLE, t0.ZTITLE2, t0.ZID, t0.ZAUTHOR, t0.ZCATEGORY FROM ZRECORD t0 WHERE t0.Z_PK IN (?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,? ) ORDER BY t0.ZTITLE LIMIT 26


If I remove the setFetchBatchSize, there's no problem (but startup requires 16 seconds). It seems that when I update the property ISFAV, CoreData needs to execute again all the fetchRequests that were needed to reach that record, even if I pass that record to the detail viewController as object.

Sorry for the long post, I tried to be as clearer as possible.
Thank you very much, I'm driving myself crazy...