[Backup] Experimentation of react-native-mmkv to store local backup config

[zatteo]

This branch is not meant to be merged. It is just an experimentation to understand the advantages, drawbacks and implications of react-native-mmkv.

Backup current implementation uses react-native-async-storage to store local backup config. I decided to store the FULL config (backup status, uploaded media list, media to upload list, ...) in ONE key as a stringified JSON object to avoid any state issue.

But this lead to multiples issues because the local backup config can take tens of MB when there are a lot of medias, so we have :

• very slow read and write on iOS and Android
• cursor issues on Android (solved here)
• cursor issues on Samsung devices (not solved)

There are multiple solutions to these issues. Here I try react-native-mmkv instead of react-native-async-storage which is known to be very fast. It may be a quick win without changing the algorithm too much and benefiting the entire app.

In this branch, I only try react-native-mmkv with backup feature.

Performance result

	react-native-async-storage	react-native-mmkv
getData read 1	87.39 ms.	21.07 ms. 😍
getData parse 1	77.93 ms.	113.39 ms. ⁉️
getLocalBackupConfig 1	166.04 ms.	136.83 ms.
getData read 2	86.70 ms.	9.45 ms. 😍
getData parse 2	91.78 ms.	152.54 ms. ⁉️
getLocalBackupConfig 2	179.14 ms.	163.91 ms.
storeData parse	66.36 ms.	83.10 ms.
storeData write	1609.73 ms.	205.22 ms. 😍

We can see a 5x to 10x performance boost. UX is better. I do not understand the parsing differences and I do not know if they are relevant.

Other results

• With RN < 0.71, we need to install react-native-mmkv 2.5.1.
• To migrate completely, we should before use /lib/localStore/storage helpers everywhere before.
• Migration code supplied by react-native-mmkv seems to work correctly.

Tested

• very slow read and write on iOS and Android : SOLVED
• cursor issues on Android : SOLVED
• cursor issues on Samsung devices : SOLVED