What does “GC--” mean in a java garbage collection log?

Question

We\'ve turned on verbose GC logging to keep track of a known memory leak and got the following entries in the log:

...
3607872.687: [GC 471630K->390767K(4         


        

Answer 1

Actually, after encountering this in our own logs, a co-worker and I have an alternative explanation that seems to fit the facts more tightly.

You'll notice in this example that a Full GC follows this weird minor GC line. I can confirm that this is always the case when it crops up in our logs. You can also see that the beginning and end size of the Young Gen is equal, and I can again confirm that this is always the case.

We believe that what is happening here is that the VM has started a Minor GC and, after either not being able to free anything or spending too long without being able to free anything, decides to do a Full instead.