问在地图上从sqlite查看引脚，我怎样才能使它更快？

EN

- (void) readDB
{
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *docDir = [paths objectAtIndex:0];

    NSString *filename = @"places.db";
    NSString *filedocPath = [docDir stringByAppendingPathComponent:filename];

    BOOL success;
    NSFileManager *fileManager = [NSFileManager defaultManager];
    success = [fileManager fileExistsAtPath:filedocPath];

    if(success == NO)
    {
        NSString *configPathFromApp = [[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:filename];

        [fileManager copyItemAtPath:configPathFromApp toPath:filedocPath error:nil];
        [fileManager release];
    }

    FMDatabase* db = [FMDatabase databaseWithPath:filedocPath];
    if (![db open]) {
        NSLog(@"Could not open db.");
        return;
    }

    // kind of experimentalish.
    [db setShouldCacheStatements:YES];


/*read*/
    for(int i = 0; i <colNum; i++)
    {
        [poi_Infos addObject:[[NSMutableArray alloc] init]];
    }

    NSString *queryString=[NSString stringWithFormat:@"select Category as %@,* from Places",categoryName];
    FMResultSet *rs = [db executeQuery:queryString];
    while ([rs next])
    {
        // just print out what we've got in a number of formats.
        [ [poi_Infos objectAtIndex:0] addObject:[rs stringForColumn:@"Company Name"]];
        [ [poi_Infos objectAtIndex:1] addObject:[NSNumber numberWithDouble:[[rs stringForColumn:@"Latitude"] doubleValue]] ];
        [ [poi_Infos objectAtIndex:2] addObject:[NSNumber numberWithDouble:[[rs stringForColumn:@"Longitude"] doubleValue]] ];
    }
    [rs close];  

    [db close];

    //NSLog(@"%@,%@", [[poi_Infos objectAtIndex:0] objectAtIndex:0],[[poi_Infos objectAtIndex:1] objectAtIndex:0]);

}

- (void) displayLocalPOI
{
    CLLocationCoordinate2D CurrentLocation;

    CurrentLocation=map.userLocation.coordinate;



    //set the radius in km so that you will get the nearest location in that radius

    double radius=localSearchRadius;


    int num = [[poi_Infos objectAtIndex:0] count];
    for(int i = 0; i < num; i++)
    {
        double y = [[[poi_Infos objectAtIndex:1] objectAtIndex:i] doubleValue];
        double x = [[[poi_Infos objectAtIndex:2] objectAtIndex:i] doubleValue];

        if(y>=CurrentLocation.latitude-(radius/111)&&y<=CurrentLocation.latitude+(radius/111))
        {
            if(x>=CurrentLocation.longitude-(radius/111)&&x<=CurrentLocation.longitude+(radius/111))
            {

                CLLocationCoordinate2D coord = CLLocationCoordinate2DMake(
                                                                          (CLLocationDegrees)y, 
                                                                          (CLLocationDegrees)x);

                NSString *title = [[poi_Infos objectAtIndex:1] objectAtIndex:i];

                UserAnnotation *userAnnotation = [[UserAnnotation alloc] initWithCoordinate:coord];
                userAnnotation.title = title;
                [self.mapAnnotations addObject:userAnnotation];

                [userAnnotation release];
            }
        }



    }



}