核心数据多NSManagedObjectContext性能难题

Question

我有一个iOS核心数据性能问题,我一直无法弄清楚.我的应用程序有一个相对简单的UICollectionViewController,它具有创建NSFetchedResultsController的功能,大致如下所示:

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)
    ....
}

我的核心数据堆栈大致类似于以下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的核心数据和博客文章中看到的基本模式.

// 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
    }
}()

问题是当我有两个像上面这样的上下文时,上面的初始fetchedResultsController.performFetch()比我只有一个(.MainQueueConcurrencyType)上下文的时间长了大约10倍.

例如,在iPad Air上使用两个上下文和大约1,700个对象执行上面的获取需要5秒钟,但只需要一个上下文(如下所示)不到0.4秒.

// 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Core Data日志记录(-com.apple.CoreData.SQLDebug 1),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SQL数据库加载的,用于初始获取.但是如果我只有一个上下文,则最初没有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.

所以根据这些结果,我修改了loadCollection函数来添加

fetchRequest.includesPropertyValues = false 

现在有两个对象上下文,我得到以下内容,初始加载时间回到0.4秒以下 - 非常好!:

    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一个错误,并导致一行SQL查询,这显着减慢了集合视图的滚动速度:

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>

使用单个上下文和includesPropertyValues默认为true,而不是像这样100个左右的批次:

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.

任何有关更好的方法的想法或建议将非常感激.

Answer 1

这是NSFetchedResultsController和 Batch Size的一个已知问题。您无法在不丢失batchSize 功能的情况下使用父子上下文。有关详细信息，请参阅此答案。

换句话说，如果您需要使用 NSFetchedResultsController 并需要最佳性能，则必须将其附加到主线程上下文，并且该上下文必须附加到持久存储协调器。