Coordinated Restore at Checkpoint (CRaC) is a technology developed by Azul within the OpenJDK project, that dramatically reduces Java application startup times by creating checkpoints and restoring JVM state. These posts explore CRaC implementation, use cases, and performance benefits for modern Java applications.
Coordinated Restore at Checkpoint (CRaC) is a JDK project, initiated by Azul. With CRaC, you can start Java programs with a shorter time to first transaction, combined with less time and resources to achieve full code speed. This is achieved by taking a snapshot (checkpoint) of a fully warmed-up Java process and launching one or more new JVMs from that snapshot.
On July 15th of 2023, I published a post here about my initial experiments with CRaC on the Raspberry Pi. At that time, I found out that both the Linux kernel in Raspberry Pi OS and the Zulu Build of OpenJDK still needed some changes to work on the Raspberry Pi. I created a ticket in the Linux kernel project, which was solved by Phil Elwell. Last week, a new version of the Raspberry Pi OS, based on Debian Bookworm, was released. And in september, version 21 of OpenJDK was released and the Zulu Build of it, includes CRaC. So let’s see if we can use CRaC without issues, if we bring all this togheter.
With the April release of the Zulu Build of OpenJDK, Azul announced the integration of CRaC in its version 17 of Java for Linux. Coordinated Restore at Checkpoint (CRaC) is a feature introduced in OpenJDK to improve Java’s application startup and warmup times to milliseconds from seconds or even minutes, by allowing a running application to pause, snapshot its state, and restart later, even on a different machine.