How to detect if the VM is running with compact refs from within the VM (no agent)?

Dawid Weiss dawid.weiss at
Wed Mar 14 01:44:13 PDT 2012

Thanks Kris!

I thought about parsing command-line but I wasn't sure about the
runtime -- can it switch to compressed OOPS on its own (or rather: is
there a heuristic to switch to compressed OOPS or is it always full
refs in 64 bit mode unless an explicit command line option's been


> You could use HotSpotDiagnosticMXBean via JMX to get VM options. An example
> here [1].
> If you're trying to get this information from the command line, use:
>   jinfo -flag UseCompressedOops <pid>
> HTH,
> - Kris
> [1]:
> On Wed, Mar 14, 2012 at 4:30 PM, Dawid Weiss <dawid.weiss at> wrote:
>> Hi everyone,
>> This has been asked on Apache Lucene JIRA and I admit I don't know the
>> answer:
>> Is there a way to detect the reference size (which boils down to
>> compact vs. full reference on 64 bit machines) from within Java?
>> I assume the VM starts without an agent so Instrumentation is not
>> available. I'd appreciate a comment if somebody knows right away (even
>> if it's a: "no"), otherwise I'll go through the sources and try to
>> figure it out on my own.
>> Thanks,
>> Dawid

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