Re: CoreData fetch is way too slow
Re: CoreData fetch is way too slow
- Subject: Re: CoreData fetch is way too slow
- From: Bill Dudney <email@hidden>
- Date: Tue, 5 Feb 2008 12:58:02 -0700
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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