What is Java PermGen garbage collector?

Question

List of garbage collectors:

• Serial GC
• Parallel gc
• Parallel Old GC
• Conc Mark Sweep GC
• G1 GC

I know that Conc Mark Sweep GC supports PermGen cleanup when you enable the ClassUnloading JVM option. Do other garbage collectors support PermGen cleanup?

Reason: we use Spring, Hibernate and Groovy, which create a lot of Proxies, and Perm Gen is getting big.

Edit: I must mention that I am using Java 7. I know that Java 8 removes Perm Gen and hopefully updates sometime in the future. In the meantime, my question is whether other garbage collectors support PermGen cleanup besides Conc Mark Sweep.

• Serial GC
• Parallel GC (Believe-server uses this by default and confirmed that it clears perm gen)
• Parallel Old GC
• Conc Mark Sweep GC (you can clear perm gen with the JVM flag)
• G1 GC

Answer 1

All algorithms clear PermGen, but

• not every GC cycle includes PermGen cleanup.
• CMS can clear PermGen at the same time , G1 requires stop-the-world Full GC to unload classes (pure PermGen) to Java 8u40
• Java 8 has meta-pass, not PermGen, but it must also be garbage-collected (otherwise you will get OOME in the meta definition)

I struggle a lot with OOME in PermGen when I actively used ClassLoaders to simulate multiple JVMs in the same process for testing. My conclusion: PermGen GC is just not very reliable. One run works as expected, the other it throws OOEM.