How Server-Driven UI Affects App Cold Start Times: A Real Benchmarking Study (Flutter Edition)

Introduction

When companies adopt Server-Driven UI (SDUI) architectures, one common concern arises:

"How much will my app's cold start performance be affected?"

At Digia, we believe in backing decisions with data.In this study, we measure and compare Flutter Native app startup performance versus Flutter + Digia SDK integration, across multiple initialization modes.

This article complements our earlier discussion:👉 Server-Driven UI vs Client-Driven UI: Performance Benchmarks You Need to Know (Flutter Edition)

Benchmarking Setup

We prepared three APK builds:

Flavor	Description
No Digia	Pure Flutter app without Digia SDK
Cache Init	Digia SDK initialized from device-local cache
Network Init	Digia SDK initialized by fetching config from server

Each build measured:

• 🚀 Cold Start Time: App launch until first screen paints

• ⏳ Digia SDK Init Time: SDK loading and applying configuration
  

How We Set Up the Code

You can view the full benchmarking project and scripts here:👉 GitHub: flutter_digia_comparison

Summary of setup:

1. Cold Start Stopwatch in main.dart

At the beginning of app launch:

final Stopwatch startupStopwatch = Stopwatch();

Future<void> main() async {

  WidgetsFlutterBinding.ensureInitialized();

  startupStopwatch.start();

}

2. Measuring Digia SDK Initialization

Separately tracking SDK init:

if (initMode != 'noDigia') {

  final Stopwatch digiaInitStopwatch = Stopwatch()..start();

  await DigiaUIClient.init(...);

  DUIFactory().initialize();

  digiaInitStopwatch.stop();

  print('⏳ Digia SDK Init Time: ${digiaInitStopwatch.elapsedMilliseconds} ms');

}

3. Capturing Cold Start Completion

When the landing screen is shown:

if (startupStopwatch.isRunning) {

  startupStopwatch.stop();

  final coldStartTime = startupStopwatch.elapsedMilliseconds;

  print('🚀 Cold Start Time: $coldStartTime ms');

}

4. Automating Testing

Using a custom script:

• Force-stop app

• Launch app via adb monkey

• Parse logs (adb logcat)

• Save Cold Start and SDK Init times into CSVs
  

Test Results

After 50 cold launches per flavor:

Mode	Avg Cold Start (ms)	Avg Digia Init (ms)
No Digia	~20ms	0ms
Cache Init	~68ms	~40ms
Network Init	~190ms	~165ms

Observations:

• No Digia has the lowest startup time (~20ms).

• Cache Init adds minimal overhead (~40ms Digia Init inside ~68ms total startup) — almost negligible impact.

• Network Init shows higher cold start penalty because it waits for real-time config download (~165ms).
  

Interpretation

Mode	Impact
No Digia	Fastest boot. No dynamic UI capabilities.
Cache Init	Near-native performance with full flexibility. Digia Init Time is almost negligible.
Network Init	Higher delay, useful for apps needing real-time server-controlled updates.

✅ In real-world scenarios, cache-first initialization gives the best user experience — barely adding any perceptible delay compared to pure Flutter.

Closing Thoughts

This real-world experiment shows that Server-Driven UI, when thoughtfully designed, does not significantly hurt app launch speeds.

• Cache-first SDK initialization gives near-native startup.

• Server-driven flexibility can be achieved without unacceptable latency.

• Developers can confidently choose Digia SDUI with optimized startup strategies.

At Digia, we continue pushing the limits — enabling speed, experimentation, and great user experience.