66 lines
3.2 KiB
Plaintext
66 lines
3.2 KiB
Plaintext
[[cds]]
|
|
= CDS
|
|
:page-aliases: integration/class-data-sharing.adoc
|
|
|
|
Class Data Sharing (CDS) is a https://docs.oracle.com/en/java/javase/17/vm/class-data-sharing.html[JVM feature]
|
|
that can help reduce the startup time and memory footprint of Java applications.
|
|
|
|
To use this feature, a CDS archive should be created for the particular classpath of the
|
|
application. The Spring Framework provides a hook-point to ease the creation of the
|
|
archive. Once the archive is available, users should opt in to use it via a JVM flag.
|
|
|
|
== Creating the CDS Archive
|
|
|
|
A CDS archive for an application can be created when the application exits. The Spring
|
|
Framework provides a mode of operation where the process can exit automatically once the
|
|
`ApplicationContext` has refreshed. In this mode, all non-lazy initialized singletons
|
|
have been instantiated, and `InitializingBean#afterPropertiesSet` callbacks have been
|
|
invoked; but the lifecycle has not started, and the `ContextRefreshedEvent` has not yet
|
|
been published.
|
|
|
|
To create the archive, two additional JVM flags must be specified:
|
|
|
|
* `-XX:ArchiveClassesAtExit=application.jsa`: creates the CDS archive on exit
|
|
* `-Dspring.context.exit=onRefresh`: starts and then immediately exits your Spring
|
|
application as described above
|
|
|
|
To create a CDS archive, your JDK must have a base image. If you add the flags above to
|
|
your startup script, you may get a warning that looks like this:
|
|
|
|
[source,shell,indent=0,subs="verbatim"]
|
|
----
|
|
-XX:ArchiveClassesAtExit is unsupported when base CDS archive is not loaded. Run with -Xlog:cds for more info.
|
|
----
|
|
|
|
The base CDS archive can be created by issuing the following command:
|
|
|
|
[source,shell,indent=0,subs="verbatim"]
|
|
----
|
|
$ java -Xshare:dump
|
|
----
|
|
|
|
== Using the Archive
|
|
|
|
Once the archive is available, add `-XX:SharedArchiveFile=application.jsa` to your startup
|
|
script to use it, assuming an `application.jsa` file in the working directory.
|
|
|
|
To figure out how effective the cache is, you can enable class loading logs by adding
|
|
an extra attribute: `-Xlog:class+load:file=cds.log`. This creates a `cds.log` with every
|
|
attempt to load a class and its source. Classes that are loaded from the cache should have
|
|
a "shared objects file" source, as shown in the following example:
|
|
|
|
[source,shell,indent=0,subs="verbatim"]
|
|
----
|
|
[0.064s][info][class,load] org.springframework.core.env.EnvironmentCapable source: shared objects file (top)
|
|
[0.064s][info][class,load] org.springframework.beans.factory.BeanFactory source: shared objects file (top)
|
|
[0.064s][info][class,load] org.springframework.beans.factory.ListableBeanFactory source: shared objects file (top)
|
|
[0.064s][info][class,load] org.springframework.beans.factory.HierarchicalBeanFactory source: shared objects file (top)
|
|
[0.065s][info][class,load] org.springframework.context.MessageSource source: shared objects file (top)
|
|
----
|
|
|
|
TIP: If you have a large number of classes that are not loaded from the cache, make sure that
|
|
the JDK and classpath used by the commands that create the archive and start the application
|
|
are identical. Note also that to effectively cache classes, the classpath should be specified
|
|
as a list of JARs containing those classes, and avoid the usage of directories and `*`
|
|
wildcard characters.
|