Re: CoreData fetch is way too slow

FROM : Bill Dudney
DATE : Tue Feb 05 20:58:02 2008

Hi James,

Though I don't know for sure it sounds to me like you don't have an 
index on the 'input' field. If I remember correctly there is checkbox 
on the field in the model editor that says 'indexed' and if you turn 
that on the SQLite store will put an index on that field which will 
make your fetches much much faster.

There could be issues with the 'like' part of your query even after 
you make an index, but i'm not hip enough on SQLite to say one way or 
the other.

http://www.sqlite.org/optoverview.html

has some guidelines to optimizing things.

HTH,

-bd-
http://bill.dudney.net/roller/objc

On Feb 5, 2008, at 12:31 PM, James Hober wrote:

> I have a CoreData app that has a SQLite store holding 157,273 
> managed objects.  Each managed object has 2 attributes, input and 
> answer, which are NSStrings and that's all.  No other attributes. 
> No relationships.  No fetched properties.
>
> A simple fetch for a single managed object takes 7 seconds!
>
>    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"%K 
> like %@",
>        @"input", input]; //assume NSString *input exists
>    NSFetchRequest *fetchRequest = [[[NSFetchRequest alloc] init] 
> autorelease];
>    NSEntityDescription *entity = [NSEntityDescription 
> entityForName:@"MyEntity"
>                                              inManagedObjectContext:
> [self managedObjectContext]];
>    [fetchRequest setEntity:entity];
>    [fetchRequest setPredicate:predicate];
>    [fetchRequest setFetchLimit:1];
>    NSError *error = nil;
>
>    //The following line takes 7 seconds to execute:
>    NSArray *results = [[self managedObjectContext] 
> executeFetchRequest:fetchRequest error:&error];
>
>    if ([results count]) {return [[results objectAtIndex:0] 
> valueForKey:@"answer"];}
>    return @"";
>
> How can I speed this up?
>
> The 157,273 inputs are unique.  I believe CoreData searches them 
> linearly in no particular order, instead of sorting them so they can 
> be binary searched in the store.  Is this aspect of CoreData 
> opaque?  Is there no way to get CoreData to efficiently search on a 
> unique string attribute?
>
> If my experiments with CoreData continue to prove unfruitful, I may 
> remain with my current implementation which uses Objective-C++  and 
> an STL map.  I can load all the data into the map in about 3.6 
> seconds and then retrieval from memory is near instantaneous.
>
> Thank you for any help speeding up this CoreData implementation or 
> any other suggestions.
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