我有一个iOS核心数据性能问题,我还没有完全解决。我的应用程序有一个相对简单的UICollectionViewController,它有一个创建NSFetchedResultsController的函数,大致如下:
func loadCollection(collectionID: String) {
let fetchRequest = NSFetchRequest(entityName: "Story")
fetchRequest.predicate = NSPredicate(format: "collectionID == %@ AND wasDeleted == FALSE", collectionID)
fetchRequest.sortDescriptors = [NSSortDescriptor(key: "yearMonthDay", ascending: true), NSSortDescriptor(key: "startDate", ascending: true)]
fetchRequest.fetchBatchSize = 100
self.fetchedResultsController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: mainObjectContext!,
sectionNameKeyPath: "yearMonth", cacheName: collectionID)
var error: NSError?
self.fetchedResultsController.performFetch(&error)
....
}
我的核心数据堆栈看起来大致像下面的两个托管对象上下文,以改善新的和编辑的"Story“对象的对象保存的UI响应时间。这是我在Marcus Zarra的核心数据手册和blog post等地方看到的基本模式。
// Variation "A" with two managed object contexts.
lazy var mainObjectContext: NSManagedObjectContext? = {
if let coordinator = self.persistentStoreCoordinator {
self.rootContext = NSManagedObjectContext(concurrencyType: .PrivateQueueConcurrencyType)
self.rootContext?.persistentStoreCoordinator = coordinator
let managedObjectContext = NSManagedObjectContext(concurrencyType: .MainQueueConcurrencyType)
managedObjectContext.parentContext = self.rootContext
return managedObjectContext
} else {
return nil
}
}()
问题是,当我有两个类似上面的上下文时,上面的初始fetchedResultsController.performFetch()花费的时间大约是只有一个(.MainQueueConcurrencyType)上下文时的10倍。
例如,在iPad Air上,使用两个上下文和大约1,700个对象执行上面的fetch需要超过5秒,但如果只使用一个上下文,则需要不到0.4秒,如下所示。
// Variation "B" with one managed object context.
lazy var mainObjectContext: NSManagedObjectContext? = {
if let coordinator = self.persistentStoreCoordinator {
let managedObjectContext = NSManagedObjectContext(concurrencyType: .MainQueueConcurrencyType)
managedObjectContext.persistentStoreCoordinator = coordinator
return managedObjectContext
} else {
return nil
}
}()
我打开了核心数据日志记录(SQL1),从日志记录中我可以看到,当我有两个对象上下文时,1,700个对象中的所有属性都是从-com.apple.CoreData.SQLDebug数据库加载的,用于初始获取。但是,如果我只有一个上下文,则最初不会从数据库加载任何属性。
Log from variation "A" with two object contexts:
2015-08-18 13:31:49.761 Myapp[27646:4374573] CoreData: sql: SELECT 0, t0.Z_PK, t0.Z_OPT, t0.ZAUTOCREATED, t0.ZBLOCKS, t0.ZCHANGETOKEN, t0.ZCOLLECTIONID, t0.ZCREATIONDATE, t0.ZEDITDATE, t0.ZENDDATE, t0.ZFULLTEXT, t0.ZGLOBALID, t0.ZLOCATION, t0.ZLOCATIONTEXT, t0.ZSTARTDATE, t0.ZTAGS, t0.ZTHUMBNAILIMAGE, t0.ZTIMEZONE, t0.ZTITLE, t0.ZWASDELETED, t0.ZYEARMONTH, t0.ZYEARMONTHDAY FROM ZSTORY t0 WHERE ( t0.ZCOLLECTIONID = ? AND t0.ZWASDELETED = ?) ORDER BY t0.ZYEARMONTHDAY, t0.ZSTARTDATE
2015-08-18 13:31:52.093 Myapp[27646:4374573] CoreData: annotation: sql connection fetch time: 2.3314s
2015-08-18 13:31:55.011 Myapp[27646:4374573] CoreData: annotation: total fetch execution time: 5.2502s for 1743 rows.
2015-08-18 13:31:55.016 Myapp[27646:4374573] CoreData: sql: SELECT t0.ZYEARMONTH, COUNT (DISTINCT t0.Z_PK) FROM ZSTORY t0 WHERE ( t0.ZCOLLECTIONID = ? AND t0.ZWASDELETED = ?) GROUP BY t0.ZYEARMONTH ORDER BY t0.ZYEARMONTH
2015-08-18 13:31:55.276 Myapp[27646:4374573] CoreData: annotation: sql connection fetch time: 0.2590s
2015-08-18 13:31:55.276 Myapp[27646:4374573] CoreData: annotation: total fetch execution time: 0.2600s for 371 rows.
Log from variation "B" with one object context:
2015-08-18 13:25:19.448 Myapp[27635:4362501] CoreData: sql: SELECT 0, t0.Z_PK FROM ZSTORY t0 WHERE ( t0.ZCOLLECTIONID = ? AND t0.ZWASDELETED = ?) ORDER BY t0.ZYEARMONTHDAY, t0.ZSTARTDATE
2015-08-18 13:25:19.789 Myapp[27635:4362501] CoreData: annotation: sql connection fetch time: 0.3405s
2015-08-18 13:25:19.789 Myapp[27635:4362501] CoreData: annotation: total fetch execution time: 0.3410s for 1743 rows.
2015-08-18 13:25:19.790 Myapp[27635:4362501] CoreData: sql: SELECT t0.ZYEARMONTH, COUNT (DISTINCT t0.Z_PK) FROM ZSTORY t0 WHERE ( t0.ZCOLLECTIONID = ? AND t0.ZWASDELETED = ?) GROUP BY t0.ZYEARMONTH ORDER BY t0.ZYEARMONTH
2015-08-18 13:25:19.825 Myapp[27635:4362501] CoreData: annotation: sql connection fetch time: 0.0339s
2015-08-18 13:25:19.825 Myapp[27635:4362501] CoreData: annotation: total fetch execution time: 0.0349s for 371 rows.
因此,基于这些结果,我修改了loadCollection函数以添加
fetchRequest.includesPropertyValues = false
现在有了两个对象上下文,我得到了以下内容,初始加载时间恢复到0.4秒以下-太棒了!
2015-08-18 13:53:43.345 Myapp[27692:4414951] CoreData: sql: SELECT 0, t0.Z_PK FROM ZSTORY t0 WHERE ( t0.ZCOLLECTIONID = ? AND t0.ZWASDELETED = ?) ORDER BY t0.ZYEARMONTHDAY, t0.ZSTARTDATE
2015-08-18 13:53:43.683 Myapp[27692:4414951] CoreData: annotation: sql connection fetch time: 0.3378s
2015-08-18 13:53:43.684 Myapp[27692:4414951] CoreData: annotation: total fetch execution time: 0.3383s for 1743 rows.
2015-08-18 13:53:43.688 Myapp[27692:4414951] CoreData: sql: SELECT t0.ZYEARMONTH, COUNT (DISTINCT t0.Z_PK) FROM ZSTORY t0 WHERE ( t0.ZCOLLECTIONID = ? AND t0.ZWASDELETED = ?) GROUP BY t0.ZYEARMONTH ORDER BY t0.ZYEARMONTH
2015-08-18 13:53:43.722 Myapp[27692:4414951] CoreData: annotation: sql connection fetch time: 0.0329s
2015-08-18 13:53:43.722 Myapp[27692:4414951] CoreData: annotation: total fetch execution time: 0.0339s for 371 rows.
但是,现在为NSFetchedResultsController获取的每个对象都是错误的,并导致单行SQL查询,这会显着减慢集合视图的滚动:
2015-08-18 13:53:44.078 Myapp[27692:4414951] CoreData: sql: SELECT 0, t0.Z_PK, t0.Z_OPT, t0.ZAUTOCREATED, t0.ZBLOCKS, t0.ZCHANGETOKEN, t0.ZCOLLECTIONID, t0.ZCREATIONDATE, t0.ZEDITDATE, t0.ZENDDATE, t0.ZFULLTEXT, t0.ZGLOBALID, t0.ZLOCATION, t0.ZLOCATIONTEXT, t0.ZSTARTDATE, t0.ZTAGS, t0.ZTHUMBNAILIMAGE, t0.ZTIMEZONE, t0.ZTITLE, t0.ZWASDELETED, t0.ZYEARMONTH, t0.ZYEARMONTHDAY FROM ZSTORY t0 WHERE t0.Z_PK = ?
2015-08-18 13:53:44.081 Myapp[27692:4414951] CoreData: annotation: sql connection fetch time: 0.0011s
2015-08-18 13:53:44.081 Myapp[27692:4414951] CoreData: annotation: total fetch execution time: 0.0029s for 1 rows.
2015-08-18 13:53:44.082 Myapp[27692:4414951] CoreData: annotation: fault fulfilled from database for : 0xd00000001ad8000c <x-coredata://967F5940-D73C-48E2-A26D-E60FF87BA9F7/Story/p1718>
而不是像下面这样的100个左右的批次,单个上下文和includesPropertyValues缺省为true:
2015-08-18 14:47:44.221 Myapp[27792:4515252] CoreData: sql: SELECT 0, t0.Z_PK, t0.Z_OPT, t0.ZAUTOCREATED, t0.ZBLOCKS, t0.ZCHANGETOKEN, t0.ZCOLLECTIONID, t0.ZCREATIONDATE, t0.ZEDITDATE, t0.ZENDDATE, t0.ZFULLTEXT, t0.ZGLOBALID, t0.ZLOCATION, t0.ZLOCATIONTEXT, t0.ZSTARTDATE, t0.ZTAGS, t0.ZTHUMBNAILIMAGE, t0.ZTIMEZONE, t0.ZTITLE, t0.ZWASDELETED, t0.ZYEARMONTH, t0.ZYEARMONTHDAY FROM ZSTORY t0 WHERE t0.Z_PK IN (SELECT * FROM _Z_intarray0) ORDER BY t0.ZYEARMONTHDAY, t0.ZSTARTDATE LIMIT 100
2015-08-18 14:47:44.468 Myapp[27792:4515252] CoreData: annotation: sql connection fetch time: 0.0959s
2015-08-18 14:47:44.469 Myapp[27792:4515252] CoreData: annotation: total fetch execution time: 0.2566s for 100 rows.
2015-08-18 14:47:44.550 Myapp[27792:4515252] CoreData: sql: SELECT 0, t0.Z_PK, t0.Z_OPT, t0.ZAUTOCREATED, t0.ZBLOCKS, t0.ZCHANGETOKEN, t0.ZCOLLECTIONID, t0.ZCREATIONDATE, t0.ZEDITDATE, t0.ZENDDATE, t0.ZFULLTEXT, t0.ZGLOBALID, t0.ZLOCATION, t0.ZLOCATIONTEXT, t0.ZSTARTDATE, t0.ZTAGS, t0.ZTHUMBNAILIMAGE, t0.ZTIMEZONE, t0.ZTITLE, t0.ZWASDELETED, t0.ZYEARMONTH, t0.ZYEARMONTHDAY FROM ZSTORY t0 WHERE t0.Z_PK IN (?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?) ORDER BY t0.ZYEARMONTHDAY, t0.ZSTARTDATE LIMIT 100
2015-08-18 14:47:44.614 Myapp[27792:4515252] CoreData: annotation: sql connection fetch time: 0.0067s
2015-08-18 14:47:44.614 Myapp[27792:4515252] CoreData: annotation: total fetch execution time: 0.0635s for 44 rows.
任何关于更好的方法的想法或建议都将不胜感激。
发布于 2015-09-29 14:40:37
这是NSFetchedResultsController和批处理大小的已知问题。使用父子上下文时,不能不丢失batchSize功能。有关详细信息,请参阅此answer。
换句话说,如果您需要使用NSFetchedResultsController并需要最佳性能,那么您的必须将其附加到主线程上下文,且该上下文必须附加到持久存储协调器。
https://stackoverflow.com/questions/32083335
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