Faster Startup Times With Startup Tracing On Android



One of the biggest pain points we’ve heard from you is startup times on Android.

Improving Startup Times

If you use AOT today, it improves startup times drastically, but you suffer in APK size bloat. This, unfortunately, is not a bargain that most Android applications can take in this modern-day as we must keep our users at the forefront of our decisions. They also ensure that they don’t have to download a large APK just to use our services. There must be a better way forward we thought.

We wanted to make sure we address this problem head-on by giving you the best of both worlds; a performant startup experience, and minimal increase to APK size.

Starting today, we’re announcing faster starter times using Startup Tracing on Android for all versions of Visual Studio.

What is Android AOT?

The Android runtime(ART) is a managed runtime used by applications and system services on Android. ART as the runtime executes Dalvik Executables (.dex files – Dalvik EXecutable) which is a compact format to store Dalvik bytecode.

ART introduced the use of ahead-of-time (AOT) compilation by compiling entire applications into native machine code upon the installation of the application. This brings faster execution of applications and improved memory allocation. As well as garbage collection mechanisms, more accurate profiling, and much more.

To accomplish this, ART uses a utility known as dex2oat (Dalvik Executable to Of Ahead Time) to create an ELF (Executable and Linkable Format) executable. The downside requires additional time to compile. Additionally, applications take up larger amounts of disk memory to store the compiled code.

What is Mono AOT?

The Mono runtime provides an ahead-of-time (AOT) feature. Which Mono will precompile assemblies to minimize JIT time and reduce memory usage.

Mono can generate an ELF .so file on platforms that support it such as Android. It then stores a precompiled image next to the original assembly.

i.e. Mono.Android.dll →

These files can then be used by the Mono runtime and omit the JIT overhead alongside similar downsides such as Android AOT.

What is Startup Tracing?

Mono introduced a feature which allows one to use a built-in AOT profiler on an application to generate an AOT profile. The profiler conducts memory profiling, execution time profiling, and even a statistical-based sampling for profiling. This generates an AOT profile that can be used to optimize your application when using Mono’s AOT feature with a profile.

Getting Started

Startup Tracing can be used with Visual Studio 2019 Version 16.2 or Visual Studio for Mac 2019 Version 8.2. 

You can get started with Startup Tracing by editing your Android project’s .csproj file and adding the following property inside your Release <PropertyGroup>:

This can also be in the Android Options in your project settings:
Enable startup tracing with a line of code.

For more documentation on Startup Tracing, see our release notes on this topic.

This will tell Mono’s AOT compiler to enable startup tracing which uses a default profile and speed up the startup time of your Android applications when deploying.

Faster Startup Times With Startup Tracing On Android

Differences in AOT Modes

TypeStartup SpeedAPK Size
Normal2s914ms16.1 MB
AOT1s18ms34.6 MB
Startup Tracing1s518ms20.1 MB



Get the best of both worlds with startup tracing and use it in your Android apps today.

We’re continuously improving this experience and want to know your thoughts on it! For anything you believe is an issue with Startup Tracing with Android apps, please file an issue on Developer Community.

Additionally, let us know if you have any suggestions for how we can improve the Startup Tracing experience.

Jon Douglas

Program Manager, Xamarin.Android

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T. P. 2019-07-24 13:59:39
Thanks for that blog post. I am still a bit confused about what the different between the "traditional" AOT and the Startup Tracing AOT is - especially because Startup Tracing has slower startup speed than AOT and significant smaller APK sizes. Does Startup Tracing mean is only AOTs parts of the app (the parts that impact app startup) and normal AOT precompiles the whole app? In that case the normal AOT would be still the way to go if we want optimal app performance after startup, right?
Tony Henrique 2019-07-24 14:46:45
Matteo Piccioni 2019-07-25 01:39:55
hello, Startup Tracing  - ofc, startup tracing is available also in preview channel version of visual studio? - could I enable it on debug too? thanks
Luis Capelo 2019-07-25 02:56:51
I've tried enabling this and don't see any visible improvement in the app loading time.still takes around 10 seconds to get past the splash screen... which is very slow. I can see a lot of libaot-***.so files in the package lib folders, so it must be doing *something*, just not something that seems a difference :(
Massimiliano Cristarella 2019-07-25 07:16:43
Hi, I noticed that if in the project name/path there are spaces and the startup tracing is enabled it doesn't compile end it gives you this error: Gravità Codice Descrizione Progetto File Riga Stato eliminazioneErrore  XA0000: Unhandled exception: System.ArgumentException: Caratteri non validi nel percorso.   in System.IO.Path.CheckInvalidPathChars(String path, Boolean checkAdditional)   in System.IO.Path.GetFileName(String path)   in Xamarin.Android.Tasks.Aot.<>c__DisplayClass77_0.<RunParallelAotCompiler>b__0(Config config)   in Xamarin.Android.Tasks.AsyncTaskExtensions.<>c__DisplayClass0_0`1.<ParallelForEach>b__0(TSource s)    0  
Mark Adamson
Mark Adamson 2019-07-25 10:09:37
Is the APK size aspect less relevant for apps that allow the play store to unbundle the apk and repackage for each platform? Or is the AOT-induced increase in size a per-platform thing? Sorry I can't remember the term for google's rebundling and don't know if Xamarin supports it or not.
Miha Markic 2019-07-31 00:55:37
Does it make sense to set EnableLLVM to true with AndroidEnableProfiledAot in VS Community edition?
ptk 2019-08-01 21:39:01
This has been failing for us when packaging/archiving the app. Create a brand new Xamarin Android app, adding the AndroidEnableProfiledAot option, then Build - Archive. The build succeeds but the packaging/archiving fails. The only error is "Cannot create the archive file because the packaging process failed".  Any idea where to find further info on this? This is Visual Studio 16.2
Piotrek 2019-08-08 23:50:04
Hi I try to use AOT option, but I cannot compile project due to linker error. Do I need add linker config to my project? Will AOT enable link user assemblies ?
Corné 2019-08-09 02:03:42
Unfortunately my app crashes during startup when I enable this. Any suggestions on how or where to find out what's causing the crash?