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，其函数创建一个NSFetchedResultsController，大致如下所示：

=A0

我的核心数据堆栈大致如下所示，带有两个托管对象上下文，以改善新的和编辑过的“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blog post等地看到的基本模式。

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)
    ....
}

问题在于，当我有两个上面的上下文时，上面的初始fetchedResultsController.performFetch（）比我只有下面的单个（.MainQueueConcurrencyType）上下文时长大约10倍。

例如，使用两个上下文和大约1,700个对象在iPad Air上执行上面的提取需要5秒钟，但只需要一个上下文就会少于0.4秒。

// 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
    }
}()

我启用了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数据库加载的初始提取。但是如果我只有一个上下文，那么最初没有从数据库加载任何属性。

// 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
        }
    }()

基于这些结果，我修改了loadCollection函数以添加

    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.

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！：

fetchRequest.includesPropertyValues = false

但是，现在为NSFetchedResultsController获取的每个对象都是一个错误，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 13:53:43.345 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.

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

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>

任何有关更好方法的想法或建议都将非常受欢迎。

Answer 1

NSFetchedResultsController 和批量大小是一个已知问题。您不能在不丢失batchSize功能的情况下使用Parent-Child上下文。有关详细信息，请参阅此answer。

换句话说，如果您需要使用NSFetchedResultsController并且需要最佳性能，必须将其附加到主线程上下文，并且必须必须附加到持久性存储协调器。

核心数据多NSManagedObjectContext性能难题

1 个答案: