Core Data和iOS 7：持久存储的不同行为

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我正在为基于Core Data的应用程序准备iOS 7的修补程序的更新。我使用Xcode 5和iOS 7 SDK GM。然而，我意识到持久存储的不同行为（这是一个 UIManagedDocument ）：在iOS 7构建之前，只有一个文件 persistentStore 在文档文件夹（有时有第二个 persistentStore-journal ）。

I'm preparing an update for a Core Data based app for fixes with iOS 7. I use Xcode 5 and iOS 7 SDK GM. However I realized a different behavior of the persistent store (which is a UIManagedDocument): Prior to iOS 7 builds there was only one file persistentStore in the documents folder (sometimes there was a second one persistentStore-journal).

7 builds（clean installation）现在有三个文件用于永久存储：

In iOS 7 builds (clean installation) there are now three files for the persistent store:

• persistentStore
• persistentStore-wal 和
• persistentStore-shm

• persistentStore
• persistentStore-wal and
• persistentStore-shm

Apple现在是否将日志模式更改为WAL？我想知道是否有影响我的应用程序（想想用户如何更新从上一个版本）？最好禁用WAL - 如果是，我该如何使用iOS 7 / UIManagedDocument ？

Did Apple change the journal mode by default to WAL now? I wonder if there is an impact on my app (think of users how update from the last version)? Would it be best to disable WAL - and if so, how can I do this with iOS 7/UIManagedDocument?

推荐答案

是的，Apple已经将iOS7的默认日记帐模式更改为WAL。 在调用addPersistentStoreWithType：configuration：url：options：error时，可以通过将NSSQLitePragmasOption添加到选项中来指定日志模式。例如。设置以前的默认模式DELETE：

Yes, Apple have changed the default journal mode to WAL for iOS7. You can specify the journal mode by adding the NSSQLitePragmasOption to the options when calling addPersistentStoreWithType:configuration:url:options:error. E.g. to set the previous default mode of DELETE:

NSDictionary *options = @{ NSSQLitePragmasOption : @{@"journal_mode" : @"DELETE"} };

在我的经验中，WAL提供更好的性能，但也看到这篇文章：

In my experience WAL gives better performance, but also see this post:

iOS CoreData - 启用sqlite WAL / Write-Ahead记录有什么缺点

iOS CoreData - are there any disadvantages to enabling sqlite WAL / Write-Ahead Logging