Project Leyden: Improving Java’s Startup Time by Per Minborg, Sébastien Deleuze

Project Leyden aims to improve Java startup time, warm-up performance, and memory footprint while maintaining Java’s dynamic capabilities

CDS (Class Data Sharing) and AOT (Ahead of Time) cache are key components that allow:

• 2-4x faster startup times
• Better initial performance without waiting for JIT compilation
• 20% reduced memory consumption for Spring applications

Main constraints for using CDS/AOT cache:

• Must use consistent classpath between training and deployment
• Need to perform training runs to generate optimization data
• Limited to JAR files (no directories, wildcards, or nested JARs)

Project Leyden vs alternatives:

• More compatible than GraalVM Native Image
• Simpler to implement than Project CRaC
• Maintains Java’s dynamic features
• Requires minimal code changes

Spring Boot 3.3 integration:

• Built-in support for CDS and AOT cache
• Automatic training run execution
• Container-friendly deployment
• Simple flag-based activation

Key benefits demonstrated:

• Pet Clinic sample starts in 800ms vs 3.2s
• Reaches peak performance faster
• No significant performance tradeoffs
• Works with existing applications

Future developments:

• More optimization opportunities being explored
• Better integration with build tools
• Improved memory consumption focus
• Additional performance improvements planned