G1 collector consuming up to ~35GB memory?

Peter B. Kessler Peter.B.Kessler at Oracle.COM
Thu Jul 19 19:06:11 UTC 2012

If you don't mind sharing, what kinds of collection times are you seeing with G1 (and with the ParallelOld collector if you have those numbers) on heaps of these sizes?

			... peter

Neil Ferguson wrote:
> Hi all.
> When using the G1 collector with large heap sizes I'm seeing the JVM 
> process grow much larger than my heap size, sometimes by as much as 
> 35GB. Here are some examples:
> Heap size 60GB, java process size: 85GB
> Heap size 120GB, java process size: 158GB
> Heap size 240GB, java process size: 274GB
> Heap size 480GB, process killed by Linux
> I'm quoting the resident set as reported by the Linux ps command. The 
> virtual memory size of the process is typically a few GB larger. This is 
> on a machine with 512GB RAM, running Linux  2.6.32-220.el6.x86_64 and 
> Java 1.7.0_05-b05.
> Typically the process size grows gradually over the first 30 minutes or 
> so of my test, then flattens out and doesn't grow any more. I'm running 
> a fairly trivial benchmark, which repeatedly adds items to a bounded 
> (LRU) cache. There's typically around 10GB free on the heap in each of 
> my tests.
> Does anyone know if this is the expected behaviour for G1? It seems 
> rather a lot of memory to be using, over the heap size. I've run the 
> same test with the parallel collector with a heap size of 60GB, and the 
> process size stabilizes quickly to around 62GB.
> Thanks.
> Neil.

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