Support Backup and Restore

[Kiura]

The language of MMKV

React-native wrapper / C++

The version of MMKV

react-native version: v0.6.0

MMKV: v1.2.7

The platform of MMKV

Android

The installation of MMKV

Git clone

What's the issue?

Currently, it is not possible to programmatically restart an application, so it is annoying to ask the users to restart the app after a backup is restored, can this be done without restarting the app?

I assume implementing this wouldn't be hard, a reinitialize method on an MMKV instance that simply reloads the data from the files.

[lingol]

What you asked, is not that simple. While doing the file copy (from outside the MMKV framework), There's no way to guarantee that the files won't be corrupted by the running App, nor does the unsynced data in mmap-memory won't get lost.

If we are about to support backup & restore instruction, we have to do it right. It requires some heavy operations such as accruing exclusive locks of the files, replacing them robustly and re-initialize the MMKV instance.

So yes we will do it. And no it won't be quick.

[Kiura]

Alright, I missed those points when I assumed this wouldn't be hard to implement 😅

This is what I had in mind:

MMKV.stopAndClearMMAP();
// user restores backup (replaces all files in mmkv folder)
MMKV.initialize(); // or MMKV.reinitialize();

Of course, the stopAndClearMMAP means that there should be a way to not do any operations on files, which involves some kind of locks to be added or a global variable, e.g.:

public String decodeString(String key) {
  if (this.stopped) {
    return "";
  }
}

Or maybe a file reader/writer interfaces can be replaced with dummy ones when the stopAndClearMMAP method is called until reinitialize is called?
I am not sure how interfaces work in c++ (sorry a golang guy here 😅)

Anyways those are just the thoughts I had once I read your reply.

Also, I know it won't be quick as you mentioned earlier, but are there any estimates (like a month, three months or a year), roadmap or maybe a bug bounty so people can influence the priorities?

Sorry for so many questions :)
Thank you for the database library, it is best out there!

[lingol]

I will say in 3 months or sonner, but no guarantee about that.
As for MMKV's roadmap, check out https://github.com/Tencent/MMKV/projects/2

[Kiura]

Great, thank you for all updates :)

[lingol]

Supported in v1.2.11.

[aemre]

Where is the docs about restore?