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

[sangheon.kim at oracle.com]

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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>
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