Using Image Compression on Checkpoint

Table of Contents

Example With Compression

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CRaC has built-in compression for checkpoints. You can use this approach in case you need to save some space in return for a relatively small increase in time on restore.

To enable image compression, you must start the JVM with the additional option -XX:CRaCEngineOptions=compression=true, for example:

 java -XX:CRaCCheckpointTo=cr-dir -XX:CRaCEngineOptions=compression=true -jar my_app.jar

A checkpoint created with this additional option, can be restored without the need for additional options:

 java -XX:CRaCRestoreFrom=cr-dir

Example With Compression

You can use the following test application to compare the impact of the compression:

 public class TestCracCompression {
    static public void main(String[] args) throws InterruptedException {
        int cnt = 0;
        while (true) {
            System.out.println(cnt++);
            Thread.sleep(1000);
        }
    }
}

Compile to code to a class file to use it easily in the next steps:

 javac TestCracCompression.java

This is the output of the checkpoint creation without compression:

 # Start the application in the first terminal
$ java -XX:CRaCCheckpointTo=cr TestCracCompression
0
1
...

# Open a second terminal and create the checkpoint
$ jcmd TestCracCompression JDK.checkpoint
52794:
Command executed successfully

# In the first terminal, the application is stopped
15
16
Jun 13, 2025 10:28:31 AM jdk.internal.crac.LoggerContainer info
INFO: Starting checkpoint
[16,097s][info][crac] Checkpoint ...
Killed

# Check the size of the checkpoint
$ ls -sh cr/pages-1.img
25M cr/pages-1.img

# Restart from the checkpoint
$ java -XX:CRaCRestoreFrom=cr
17
18
...

This is the output of the checkpoint creation with compression:

 # Start the application in the first terminal with an extra command line option
$ java -XX:CRaCCheckpointTo=cr -XX:CRaCEngineOptions=compression=true TestCracCompression

# Repeat the same steps to create the checkpoint

# Check the size of the checkpoint
$ ls -sh cr/pages-1.comp.img
5,8M cr/pages-1.comp.img

As you can see in the output above, the size of the checkpoint for this test application reduces from 25MB to 6MB.