swift – 核心数据多NSManagedObjectContext性能难题

发布时间：2020-12-14 05:51:55 所属栏目：百科来源：网络整理

导读：我有一个iOS核心数据性能问题，我没有能够弄清楚。我的应用程序有一个相对简单的UICollectionViewController，具有创建NSFetchedResultsController的功能，大致如下： func loadCollection(collectionID: String) { let fetchRequest = NSFetchRequest(entit

我有一个iOS核心数据性能问题，我没有能够弄清楚。我的应用程序有一个相对简单的UICollectionViewController，具有创建NSFetchedResultsController的功能，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像以下两个管理对象上下文，以改善新的和编辑的“故事”对象的对象保存的UI响应时间。这是我在Marcus Zarra的核心数据书和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
    }
}()

问题是当我有两个如上所述的上下文时，上面的最初的fetchedResultsController.performFetch()比以前只有一个(.MainQueueConcurrencyType)上下文的时间要长约10倍。

例如，使用两个上下文和大约1,700个对象执行上面的抓取在iPad Air上占用5秒以上，但只有一个上下文不到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
        }
    }()

我打开了核心数据记录(-com.apple.CoreData.SQLDebug 1)，从日志记录我可以看到，当我有两个对象上下文时，1,700个对象的所有属性正在从SQL数据库加载以进行初始提取。但是，如果我只有一个上下文，则不会从数据库初始加载属性。

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.

所以基于这些结果，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，初始加载时间在0.4秒以下 – 优秀!:

2015-08-18 13:53:43.345 Myapp[27692:4414951] CoreData: sql: SELECT 0,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，导致一行SQL查询，这显着减慢了集合视图滚动：

2015-08-18 13:53:44.078 Myapp[27692:4414951] CoreData: sql: SELECT 0,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>

而不是使用100个左右的批次，并且includePropertyValues默认为true：

2015-08-18 14:47:44.221 Myapp[27792:4515252] CoreData: sql: SELECT 0,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.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将是最受赞赏的。

这是NSFetchedResultsController和批量大小的已知问题。您不能在不丢失batchSize功能的情况下使用Parent-Child上下文。详见 answer。

换句话说，如果您需要使用NSFetchedResultsController并且需要最佳性能，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。

（编辑：李大同）

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