RN 0.63.1 + enableHermes -> very slow launch performances

[imranMnts]

Bug Description

I recently updated RN version of my project from 0.59.10 to 0.63.1. It works properly, I didn't detect any issue but when I turn on Hermes to benefice its advantages, my app takes 2 times longer to be launched in release mode.

Versions:
Hermes version: 0.5.0
React Native version: 0.63.1
Android version: Android 8.0
Device: Samsung J3

Launch times (to see the first screen of the app):

• without hermes: ~7s
• with hermes: ~20s

If anyone has had to face this problem, your help is welcome 🙂
Thank you.

[avp]

Thanks for the report. It's easier to debug these sorts of issues with some code to look at - without it, we're in the dark regarding the actual problem.

A few things to try:

• Make sure you're in release mode
• Try putting some logging statements to try and narrow down precisely where the error is. It could be some code for which Hermes is not optimized
• JS thread randomly freezes for 5-20 seconds when using Hermes #295 has some discussion on how to track these sorts of things down.

[Huxpro]

@imranMnts any updates? Have you tried what @avp suggested (especially making sure you were in the release mode)?

[peterkuiper]

I have seen this as well. We use react-native-sodium and the decrypt function itself takes about 7s. Due to this (and maybe other packages hit by this issue), the startup time is about 15-20s (we have to load encrypted data into redux). After disabling Hermes, the startup time is about 4-7s. We are using RN 0.63.4 and testing on low end Android devices (these seem to be affected the most).

[Huxpro]

Besides of what @avp had mentioned, there is also possibility that you are not using pre-compiled bytecode. You can check if the main.jsbundle looks like JS source or bytecode. The bytecode is compiled in react-native-xcode.sh and we've seen people/codebase (e.g. Mattermost) has their own copy of react-native-xcode.sh hence the app doesn't use bytecode and fallback to Hermes's on-device lazy compilation.

[tmikov]

FWIW, startup time of 4-7s doesn't sound that great either. Perhaps the lesson here is that JavaScript, even with a JIT, is just not that suitable for high intensity computation like decryption. It would work much better if the decryption was implemented in C++.

[imranMnts]

@Huxpro
Sorry for the late response, we had some other urgent topics

I double-checked and I'm sure I'm in release mode.
I updated RN's version to 0.64.1, Hermes working fine on iOS but we have still the speed issue during the startup on android.

Hermes version: 0.7.2
RN version: 0.64.1

[imranMnts]

Thanks all

I fixed the issue on my side.

It was due to the bundle generated in the APK, it was in JS and to beneficiate from Hermes' improvements it should be bytecode.

[Huxpro]

@imgraham thanks for reporting back!

As I mentioned before, this is often the cause:

You can check if the main.jsbundle looks like JS source or bytecode.

Would you mind sharing with us how did you find it and what was the improvements?

[devjaw]

@imranMnts how did you fix it ?

[imranMnts]

we generated the bundle manually via
react-native bundle --platform android \ ...

I removed it and added

project.ext.react = [
    enableHermes: true,
]
apply from: "../../node_modules/react-native/react.gradle"

in my app/build.gradle
which generate the bundle during the compilation automatically and fix the bundle which was in js

[aemre]

we generated the bundle manually via react-native bundle --platform android \ ...

I removed it and added

project.ext.react = [
    enableHermes: true,
]
apply from: "../../node_modules/react-native/react.gradle"

in my app/build.gradle which generate the bundle during the compilation automatically and fix the bundle which was in js

so manually creating bundle solve the issue?

[CloudCityxx]

I also encountered this problem。 very very slow.

[CloudCityxx]

we generated the bundle manually via react-native bundle --platform android \ ...
I removed it and added

project.ext.react = [
    enableHermes: true,
]
apply from: "../../node_modules/react-native/react.gradle"

in my app/build.gradle which generate the bundle during the compilation automatically and fix the bundle which was in js

so manually creating bundle solve the issue?

I tried this solution, but it didn't solve, it was still very slow

[imranMnts]

@CloudCityxx Did you unzip your apk to check if your bundle contains bytecode or js? (in assets folder)

[upngo]

For anyone who stumbles upon this with RN 0.71.0
Upgrade to 0.71.1 as there was an issue with hermes and debug (didn't affect release builds)