workavia-mail-front/docs/adr/0079-reduce-twake-mail-mobile-memory-usage.md

0079 - Reduce Twake Mail mobile memory usage

Date: 2026-04-09

Status

Accepted

Context

Twake Mail is allocating a lot of memory on mobile.

• ~375 MB on Android (Oneplus 8T)

• ~297 MB on iOS (iPhone 11 Pro)

Findings

worker_manager library's inefficient memory allocation (Android & iOS)

• Version 5.0.3 counts the number of processors (x) on the device, create forever-live x - 1 isolates
• Version 7.2.7 adds an ability to create isolate on-demand, and dispose when done. However, it still leaks 1 isolate when init.

firebase_messaging library's eager background Dart isolate (Android)

• FirebaseMessaging.onBackgroundMessage() creates a forever-live isolate even when the app is in foreground.
• Related: https://github.com/firebase/flutterfire/issues/17163

Unused flutter_downloader library's worker (iOS)

• The only usage was deleted in https://github.com/linagora/tmail-flutter/commit/be8eaf625818b17e60ca65846053cb8c26a71a15#diff-451741ba5146e6ad711c77e4c2fe34958a36595e4926cd43c2ddb97586ef6d88, but the library and initialization process remained, causing 1 forever-live isolate.

Decision

worker_manager

• Upgrade to 7.2.7
• Create an upstream fix for init's isolate leak

firebase_messaging

• Wait for https://github.com/firebase/flutterfire/pull/18122, update when merged

flutter_downloader

• Remove the library

Consequences

• Android: ~118 MB

• iOS: ~78 MB

• No changes for web

Before	After