UseCompressedOops switch with more than 32gb heaps...

atulksh atulksh at
Thu May 27 19:08:50 UTC 2010

This is great to know.

Thank you so much for you quick responses.


Vladimir Kozlov-6 wrote:
> Very soon. Watch for next changes coming into hotspot (jdk7).
> I don't know when it will appear in the 6 update release.
> "6916623: Align object to 16 bytes to use Compressed Oops with java heap
> up to 64Gb"
> "6954029: Improve implicit null check generation with COOP"
> The first bug is closed so you may not see it but I will open it when I am
> done with changes.
> Vladimir
> atulksh wrote:
>> 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.
>> Atul
>> 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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