-XX:+UseNUMA in conjunction with -XX:+UseG1GC

[David Weeda]

Good Afternoon,

I have set the parameter in our development system however the following message is now displayed in the start-up log.
J  Option is not recommended for use in productive environments: -XX:+UseNUMA

Regards,
David Weeda
SAP Technical Architect

From: sangheon.kim at oracle.com <sangheon.kim at oracle.com>
Sent: Wednesday, 29 August 2018 6:57 AM
To: David Weeda <David.Weeda at det.nsw.edu.au>; hotspot-gc-use at openjdk.java.net
Cc: Jag Inturi <Jag.Inturi at det.nsw.edu.au>
Subject: Re: -XX:+UseNUMA in conjunction with -XX:+UseG1GC

Hi David,
On 8/26/18 11:18 PM, David Weeda wrote:
Hello,

We are upgrading our SAP Java Application servers to use SAP JVM 8.1 Patch Collection 39. This release integrates updates from Oracle JDK 8u172

The GC shall be switched from -XX:+UseConcMarkSweepGC to -XX:+UseG1GC.

On the following website:-
https://docs.oracle.com/javase/8/docs/technotes/guides/vm/performance-enhancements-7.html#numa
There is a note on NUMA Collector Enhancements for the Parallel Scavenger garbage collector. Are the subsequent collectors, namely the G1 garbage collector also NUMA aware?
No, G1 is not NUMA aware. Only Parallel GC(-XX:+UseParallelGC) has NUMA awareness.


Is it default?
If you are asking UseNUMA option is by default for G1GC, no UseNUMA is always false by default.


May I use the -XX:+UseNUMA flag with -XX:+UseG1GC?
Yes, you can use +UseNUMA with +UseG1GC.
G1 algorithm is not NUMA aware, but with UseNUMA enabled, we can get NUMA interleaving. i.e. Interleave memory across NUMA nodes if possible and this would give some benefits on NUMA system.
FYI, UseNUMAInterleaving(false by default) command-line option will be automatically enabled if UseNUMA is enabled.

HTH,
Sangheon




Regards,
David Weeda
SAP Technical Architect | Enterprise Systems | Information Technology Directorate
Level 11, 8 Central Ave | Eveleigh NSW 2015 | |*:+61 (0)4 8822 0280 | *: david.weeda at det.nsw.edu.au<mailto:david.weeda at det.nsw.edu.au> | www.dec.nsw.gov.au<http://www.dec.nsw.gov.au/>

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