One common issue that developers face during Scala compilation is the `java.lang.OutOfMemoryError: PermGen Space` error. This error occurs when the Permanent Generation (PermGen) memory allocated by the JVM is exhausted. PermGen is part of the heap that stores class definitions and meta-information. Fortunately, there are ways to address this issue.
Steps to Prevent java.lang.OutOfMemoryError: PermGen Space
1. Increase PermGen Space
The simplest way to prevent this error is to increase the PermGen space allocated when running the Scala compiler or application. This can be done by modifying the JVM options.
Using SBT (Scala Build Tool)
If you are using SBT for building your Scala project, you can specify the JVM options in your `build.sbt` file or an `sbt` script. Below is an example of how to increase the PermGen space in SBT.
// In build.sbt
javaOptions ++= Seq(
"-XX:MaxPermSize=512m",
"-XX:PermSize=256m"
)
In this example, PermGen space is set to have an initial size of 256MB and a maximum size of 512MB.
Using Command Line
Alternatively, you can set the JVM options directly on the command line when running the Scala compilation or the application. Here’s an example:
“`bash
scala -J-XX:MaxPermSize=512m -J-XX:PermSize=256m MyScalaApp
“`
Disabling PermGen Completely (Java 8 and Above)
Java 8 replaces PermGen space with Metaspace, which dynamically grows as needed. If you are using Java 8 or later, you don’t need to worry about PermGen issues. Ensure you are running an updated version of Java with the following command:
“`bash
java -version
“`
Miscellaneous Tips
2. Clean Up Unused Classes and Objects
PermGen space stores class and method objects. Reducing the number of unused classes and objects may help in mitigating this issue.
3. Monitor and Profile Memory Usage
Use tools such as VisualVM or JConsole to monitor the JVM’s memory usage. Profiling may give insights into what’s consuming excessive PermGen space.
4. Use the Latest Scala and JVM Versions
Using the latest versions can help you avoid known issues related to memory management in both Scala and the JVM.
Example
Below is an example `build.sbt` that includes JVM options to increase the PermGen space.
// build.sbt
name := "MyScalaProject"
version := "0.1"
scalaVersion := "2.13.3"
javacOptions ++= Seq("-source", "1.8", "-target", "1.8")
scalacOptions ++= Seq(
"-deprecation",
"-feature",
"-unchecked",
"-encoding", "utf8"
)
// Increase PermGen space
javaOptions ++= Seq(
"-XX:MaxPermSize=512m",
"-XX:PermSize=256m"
)
Output
There is no direct output to show for configuration changes. The successful increase in PermGen space will prevent the `java.lang.OutOfMemoryError: PermGen Space` error during compilation and runtime.