In JDK 8, the Permanent Generation (PermGen) was removed and replaced by Metaspace. PermGen was a fixed-size memory area inside the JVM heap used to store class metadata, which often led to OutOfMemoryError when the allocated space was exhausted. Metaspace stores class metadata in native memory and can grow dynamically, providing better scalability and reducing memory management issues.
Key Points: • PermGen was part of the JVM heap with a fixed size, while Metaspace uses native memory outside the heap. • Metaspace grows automatically based on application needs, reducing the likelihood of metadata-related OutOfMemoryError. • JVM tuning changed from using -XX:MaxPermSize to options such as -XX:MaxMetaspaceSize.
Example: In applications that dynamically load many classes, such as application servers or frameworks, PermGen could become full and cause startup or runtime failures. Metaspace handles such workloads more efficiently by expanding as needed.
Code Example: # JDK 7 (PermGen)
-XX:PermSize=128m -XX:MaxPermSize=256m
# JDK 8+ (Metaspace)
-XX:MetaspaceSize=128m -XX:MaxMetaspaceSize=256m
Interview Tip: A concise interview answer is: JDK 8 removed PermGen and introduced Metaspace. Unlike PermGen, which had a fixed size within the heap, Metaspace uses native memory and grows dynamically, improving scalability and reducing metadata-related OutOfMemoryError issues.