I'm seeing a substantial degradation in Core Data fetch performance after just
a few thousand objects, in the simulator on a beefy MacBook Pro.
My app loads data from the web, then uses an integer key in each downloaded
record to find the local record in Core Data. So I do a lot of queries like
this:
{
NSFetchRequest* req = [[NSFetchRequest alloc] init];
req.fetchLimit = 1;
NSManagedObjectContext* moc = self.managedObjectContext;
NSEntityDescription* entity = [NSEntityDescription entityForName:
@"MissionEvent"
inManagedObjectContext: moc];
req.entity = entity;
NSPredicate* pred = [NSPredicate predicateWithFormat: @"keyShadow == %ld",
inMEP.mId];
req.predicate = pred;
NSError* error = nil;
NSArray* events = [self.managedObjectContext executeFetchRequest: req
error: &error];
...
}
Basically, I query, the insert, over and over. As the number of records grows
from 0 to 6000, the time it takes to execute this query grows from about 0.0007
s to about 0.0126 s. Indexing is on for keyShadow:
sqlite> explain query plan SELECT 0, t0.Z_PK, t0.Z_OPT, t0.ZCLOCKSHADOW,
t0.ZDESC, t0.ZDISABLEDSHADOW, t0.ZDURATIONSHADOW, t0.ZKEYSHADOW,
t0.ZLASTMODIFIED, t0.ZNAME, t0.ZSEQUENCESHADOW, t0.ZTIMESHADOW, t0.ZTYPESHADOW,
t0.ZMISSION FROM ZMISSIONEVENT t0 WHERE t0.ZKEYSHADOW = ?
...> ;
sele order from deta
---- ------------- ---- ----
0 0 0 SEARCH TABLE ZMISSIONEVENT AS t0 USING INDEX
ZMISSIONEVENT_ZKEYSHADOW_INDEX (ZKEYSHADOW=?) (~10 rows)
This seems like pretty poor performance. Is this the best I can hope for?
Thanks,
--
Rick
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