How do you compact a Realm database on iOS?

Question

I would like to periodically copy an instance of Realm on iOS to recover space. I think the process is to copy the db to a temporary location, then copy it and use the new default.realm file.

My Realm() problem acts like a singleton and recycles objects, so I cannot close it and say it to open a new default.realm file.

The docs here ( https://realm.io/docs/objc/latest/api/Classes/RLMRealm.html ) suggest to wrap all Realm () calls in autorelease { } , but this can't be complicated.

Answer 1

It may be really difficult to completely demolish all the extracted model accessors, but unfortunately there is no other way to close the kingdom.

As you wrote “periodically”, each application launch can be quite often, depending on your use case.

When starting the application, it should be relatively easy to open Realm in the selected autoreleasepool, write a compressed copy to another path and replace the default.realm file with it.

Swift 2.1

 func compactRealm() { let defaultURL = Realm.Configuration.defaultConfiguration.fileURL! let defaultParentURL = defaultURL.URLByDeletingLastPathComponent! let compactedURL = defaultParentURL.URLByAppendingPathComponent("default-compact.realm") autoreleasepool { let realm = try! Realm() realm.writeCopyToPath(compactedURL) } try! NSFileManager.defaultManager().removeItemAtURL(defaultURL) try! NSFileManager.defaultManager().moveItemAtURL(compactedURL, toURL: defaultURL) } func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool { compactRealm() // further setup … return true } 

Swift 3.0

 func compactRealm() { let defaultURL = Realm.Configuration.defaultConfiguration.fileURL! let defaultParentURL = defaultURL.deletingLastPathComponent() let compactedURL = defaultParentURL.appendingPathComponent("default-compact.realm") autoreleasepool { let realm = try! Realm() try! realm.writeCopy(toFile: compactedURL) } try! FileManager.default.removeItem(at: defaultURL) try! FileManager.default.moveItem(at: compactedURL, to: defaultURL) } func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool { compactRealm() // further setup … return true } 

Answer 2

The answer given by @marius has a problem: open Realm may still refer to the remote file. This means that some records may appear in the old (deleted) file, as a result of which the application will lose data.

The correct implementation of the compactRealm method looks like this: (swift 3):

 func compactRealm() { let defaultURL = Realm.Configuration.defaultConfiguration.fileURL! let defaultParentURL = defaultURL.deletingLastPathComponent() let compactedURL = defaultParentURL.appendingPathComponent("default-compact.realm") autoreleasepool { let realm = try! Realm() try! realm.writeCopy(toFile: compactedURL) } try! FileManager.default.removeItem(at: defaultURL) try! FileManager.default.moveItem(at: compactedURL, to: defaultURL) } 

This problem drove me crazy until I found the answer here

Answer 3

Well .. this problem seems to be mostly outdated. Last fall, Realm added an automatic compact feature. Realm Docs / compacting-realms . I think the only reason for this, described by @marius, is that you need to control the user interface and compactly in the background.

See this question for more details: How to properly use shouldCompactOnLaunch in RealmSwift