-XX:+ForceMmapReserved

[Former Member]

Can I use this parameter -XX:+ForceMmapReserved for my server nodes for efficient memory usage.

Regards

Shaji

[Former Member · Accepted solution]

Hello Shaji,

I couldn’t find any reference to ForceMmapReserved in SAP’s databases and it is not recommended in the notes about JVM parameters. I haven’t heard about this option before and I haven’t seen any one using it. However it is recommended in articles from HP and it seems like you could achieve better performance. Therefore I recommend you to try it and do load tests if possible.

I’m posting some information about ForceMmapReserved from HP in case someone else is interested:

-XX:+ForceMmapReserved

Use this option to reserve the space for all large memory regions used by the JVM. This includes the Java Heap, which is an mmap'ed space. Starting with HP-UX 11.11, the default behavior is that the memory regions be reserved lazily. Most large server-side applications will use all of the space, so improved performance can be obtained by reserving the space at program initialization.

There is more information available at the following links:

http://www.hp.com/products1/unix/java/infolibrary/prog_guide/expanding_memory.html

http://www.hp.com/products1/unix/java/infolibrary/prog_guide/hotspot.html#-Xms

Regards,

Ventsi Tsachev

Technology Development Support (J2EE Engine)

SAP Labs, Palo Alto, Ca (USA)

[Former Member · Accepted solution]

Hi Ventsi,

This parameter really works. -XX:+ForceMmapReserved.

jlaunch process which were taking about 2GB memory each is down to 500MB.

Thereby, the mem util on the HP-UX box has come down drastically.

Though its too early to say too much of it, will update after monitoring for a month.

Thanks for your support.

Regards

Shaji

[Former Member]

Hi Ventsi,

Thanks for the information. We have scheduled the change of JDK. Will apply the parameter -XX:+ForceMmapReserved on our HP box and see the result. Will update once its done.

Regards

Shaji