UseCompressedOops switch with more than 32gb heaps...

atulksh atulksh at
Thu May 27 18:40:13 UTC 2010

Hi Vladimir,
So what you are saying is, in a future Hotspot release, we will have the
ability to specify a heap greater than 32Gb for a VM and still use the
useCompressedOops switch. The VM will use compressed oops references, while
still allowing the VM overall to address more than 32Gb of heap.

What is the timeframe of such a feature (even if it is vague and not precise
it is fine) are we looking at - is it coming soon (less than a year)?

Thanks for your quick response.


Vladimir Kozlov-6 wrote:
> I am currently working on this. You have to increase java objects
> alignment
> (from current 8 bytes) to be able to use compressed pointers (which are 32
> bit)
> which large heaps.
> Thanks,
> Vladimir
> atulksh wrote:
>> Hi,
>> We are currently running our application servers with 26Gb of heap and
>> have
>> the UseCompressedOops enabled for memory savings. We are intending to
>> boost
>> the memory on our servers more, in which event, we would be bumping the
>> heap
>> above 32Gb. I know that the UseCompressedOops switch works only if you
>> have
>> a heap of 32Gb or less.
>> Is there anything in the Hotspot VM roadmap where there may be support of
>> heaps larger than 32Gb, and still using the UseCompressedOops switch for
>> memory optimization (32 bit object pointers within the heap)? Or is this
>> question irrelevent - meaning there is no possibility to have such a
>> support
>> on the 64 bit machines?
>> Thank you for your response in advance.
>> Atul

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