Core Data 和 iOS 7:持久化存储的不同行为 [英] Core Data and iOS 7: Different behavior of persistent store
问题描述
我正在为基于 Core Data 的应用程序准备更新以修复 iOS 7.我使用 Xcode 5 和 iOS 7 SDK GM.然而，我意识到持久存储的一种不同行为(它是一个 UIManagedDocument):在 iOS 7 构建之前，文档文件夹中只有一个文件 persistentStore(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).
在 iOS 7 版本(全新安装)中，持久存储现在有三个文件:
In iOS 7 builds (clean installation) there are now three files for the persistent store:
persistentStorepersistentStore-wal和persistentStore-shm
Apple 现在是否将默认日志模式更改为 WAL?我想知道是否对我的应用程序有影响(想想用户如何从上一个版本更新)?最好禁用 WAL - 如果是这样，我该如何使用 iOS 7/UIManagedDocument 执行此操作?
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 已将 iOS7 的默认日志模式更改为 WAL.您可以通过在调用 addPersistentStoreWithType:configuration:url:options:error 时将 NSSQLitePragmasOption 添加到选项来指定日志模式.例如.设置以前的默认删除模式:
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"} };
根据我的经验，WAL 提供了更好的性能，但也可以查看这篇文章:
In my experience WAL gives better performance, but also see this post:
iOS CoreData - 有吗启用 sqlite WAL/Write-Ahead Logging 的任何缺点
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