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POFetch from CoreData and Group By categories is extremely slow
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copied!<p>I have to fetch about few hundreds records from CoreData and group them by category_id to put into sections. Below is the code for the fetchedResultController</p> <pre><code>- (NSFetchedResultsController *)fetchedResultsController { if (_fetchedResultsController != nil) { return _fetchedResultsController; } NSPredicate *predicate = [NSPredicate predicateWithFormat:@"%d == mall_id",self.mallId.intValue]; NSFetchRequest *fetch = [[NSFetchRequest alloc] initWithEntityName:@"Shop"]; NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"category_id" ascending:YES]; NSArray *sortDescriptors = [NSArray arrayWithObject:sortDescriptor]; [fetch setPredicate:predicate]; [fetch setFetchBatchSize:20]; [fetch setSortDescriptors:sortDescriptors]; self.fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetch managedObjectContext:self.contextForDb sectionNameKeyPath:@"category_id" cacheName:@"root"]; return self.fetchedResultsController; } </code></pre> <p>the fetching takes around 1-1.5 seconds which is unacceptable slow for few hundreds of records. I've tried to search on the Internet for solution for days but haven't managed to solve this performance problem.</p> <p>I think the bottle neck is the grouping on the database.</p> <p>Could somebody please help ?</p> <p><strong>UPDATE</strong></p> <pre><code>2012-04-02 17:57:08.872 SGMalls[186:707] CoreData: sql: SELECT 0, t0.Z_PK, t0.Z_OPT, t0.ZADDRESS, t0.ZID, t0.ZLATITUDE, t0.ZLONGITUDE, t0.ZNAME, t0.ZPHONE, t0.ZUPDATED_TIME, t0.ZURL, t0.ZZIP FROM ZMALL t0 WHERE t0.ZID = ? 2012-04-02 17:57:08.875 SGMalls[186:707] CoreData: annotation: sql connection fetch time: 0.0030s 2012-04-02 17:57:08.877 SGMalls[186:707] CoreData: annotation: total fetch execution time: 0.0047s for 1 rows. 2012-04-02 17:57:09.040 SGMalls[186:707] CoreData: sql: SELECT 0, t0.Z_PK FROM ZSHOP t0 WHERE ? = t0.ZMALL_ID ORDER BY t0.ZCATEGORY_ID 2012-04-02 17:57:09.390 SGMalls[186:707] CoreData: annotation: sql connection fetch time: 0.3496s 2012-04-02 17:57:09.391 SGMalls[186:707] CoreData: annotation: total fetch execution time: 0.3514s for 16 rows. 2012-04-02 17:57:09.395 SGMalls[186:707] CoreData: sql: SELECT t0.ZCATEGORY_ID, COUNT (DISTINCT t0.Z_PK) FROM ZSHOP t0 WHERE ? = t0.ZMALL_ID GROUP BY t0.ZCATEGORY_ID ORDER BY t0.ZCATEGORY_ID 2012-04-02 17:57:09.741 SGMalls[186:707] CoreData: annotation: sql connection fetch time: 0.3458s 2012-04-02 17:57:09.743 SGMalls[186:707] CoreData: annotation: total fetch execution time: 0.3475s for 3 rows. 2012-04-02 17:57:09.748 SGMalls[186:707] CoreData: sql: SELECT 0, t0.Z_PK, t0.Z_OPT, t0.ZDETAIL, t0.ZID, t0.ZNAME FROM ZCATEG t0 WHERE t0.ZID = ? 2012-04-02 17:57:09.751 SGMalls[186:707] CoreData: annotation: sql connection fetch time: 0.0028s 2012-04-02 17:57:09.754 SGMalls[186:707] CoreData: annotation: total fetch execution time: 0.0061s for 1 rows. 2012-04-02 17:57:09.757 SGMalls[186:707] Title: icon_foodspecialties 2012-04-02 17:57:09.765 SGMalls[186:707] CoreData: sql: SELECT 0, t0.Z_PK, t0.Z_OPT, t0.ZDETAIL, t0.ZID, t0.ZNAME FROM ZCATEG t0 WHERE t0.ZID = ? 2012-04-02 17:57:09.767 SGMalls[186:707] CoreData: annotation: sql connection fetch time: 0.0022s 2012-04-02 17:57:09.769 SGMalls[186:707] CoreData: annotation: total fetch execution time: 0.0042s for 1 rows. 2012-04-02 17:57:09.773 SGMalls[186:707] Title: icon_supermarket 2012-04-02 17:57:09.782 SGMalls[186:707] CoreData: sql: SELECT 0, t0.Z_PK, t0.Z_OPT, t0.ZDETAIL, t0.ZID, t0.ZNAME FROM ZCATEG t0 WHERE t0.ZID = ? 2012-04-02 17:57:09.784 SGMalls[186:707] CoreData: annotation: sql connection fetch time: 0.0022s 2012-04-02 17:57:09.787 SGMalls[186:707] CoreData: annotation: total fetch execution time: 0.0046s for 1 rows. </code></pre> <p>Enable SQL Debugging returns this in the console</p>

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