Posts Tagged ‘CDS’
[DevoxxBE2024] Project Leyden: Improving Java’s Startup Time by Per Minborg, Sébastien Deleuze
Per Minborg and Sébastien Deleuze delivered an insightful joint presentation at Devoxx Belgium 2024, unveiling the transformative potential of Project Leyden to enhance Java application startup time, warmup, and footprint. Per, from Oracle’s Java Core Library team, and Sébastien, a Spring Framework core committer at Broadcom, explored how Leyden shifts computation across time to optimize performance. Despite minor demo hiccups, such as Wi-Fi-related delays, their talk combined technical depth with practical demonstrations, showcasing how Spring Boot 3.3 leverages Leyden’s advancements, cutting startup times significantly and paving the way for future Java optimizations.
Understanding Project Leyden’s Mission
Project Leyden, an open-source initiative under OpenJDK, aims to address long-standing Java performance challenges: startup time, warmup time, and memory footprint. Per explained startup as the duration from launching a program to its first useful operation, like displaying “Hello World” or serving a Spring app’s initial request. Warmup, conversely, is the time to reach peak performance via JIT compilation. Leyden’s approach involves shifting computations earlier (e.g., at build time) or later (e.g., via lazy initialization) while preserving Java’s dynamic nature. Unlike GraalVM Native Image or Project CRaC, which sacrifice dynamism for speed, Leyden maintains compatibility, allowing developers to balance performance and flexibility.
Class Data Sharing (CDS) and AOT Cache: Today’s Solutions
Per introduced Class Data Sharing (CDS), a feature available since JDK 5, and its evolution into the Ahead-of-Time (AOT) Cache, a cornerstone of Leyden’s strategy. CDS preloads JDK classes, while AppCDS, introduced in JDK 10, extends this to application classes. The AOT Cache, an upcoming enhancement, stores class objects, resolved linkages, and method profiles, enabling near-instant startup. Sébastien demonstrated this with a Spring Boot Pet Clinic application, reducing startup from 3.2 seconds to 800 milliseconds using CDS and AOT Cache. The process involves a training run to generate the cache, which is then reused for faster deployments, though it requires consistent JVM and classpath configurations.
Spring Boot’s Synergy with Leyden
Sébastien highlighted the collaboration between the Spring and Leyden teams, initiated after a 2023 JVM Language Summit case study. Spring Boot 3.3 introduces features to simplify CDS and AOT Cache usage, such as extracting executable JARs into a CDS-friendly layout. A demo showed how a single command extracts the JAR, runs a training phase, and generates a cache, which is then embedded in a container image. This reduced startup times by up to 4x and memory usage by 20% when combined with Spring’s AOT optimizations. Sébastien also demonstrated how AOT Cache retains JIT “warmness,” enabling near-peak performance from startup, though a minor performance plateau gap is being addressed.
Future Horizons and Trade-offs
Looking ahead, Leyden plans to introduce stable values, a hybrid between mutable and immutable fields, offering final-like performance with flexible initialization. Per emphasized that Leyden avoids the heavy constraints of GraalVM (e.g., limited reflection) or CRaC (e.g., Linux-only, security concerns with serialized secrets). While CRaC achieves millisecond startups, its lifecycle complexities and security risks limit adoption. Leyden’s AOT Cache, conversely, offers significant gains (2–4x faster startups) with minimal constraints, making it ideal for most use cases. Developers can experiment with Leyden’s early access builds to optimize their applications, with further enhancements like code cache storage on the horizon.
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Hashtags: #ProjectLeyden #Java #SpringBoot #AOTCache #CDS #StartupTime #JVM #DevoxxBE2024 #PerMinborg #SébastienDeleuze