Java Heap Size Parameters meaning

[Former Member]

In Config tool I am seeing below Heapsize parameters.

-XX:MaxPermSize=512M

-XX:PermSize=512M

-Xms3072M

-XX:NewSize=340M

-XX:MaxNewSize=340M

When I went to sap notes 1303953nit show as

globalArea | -Xps

initialHeapSize | -Xms

maxHeapSize | -Xmx

maxNewSize | -XX:MaxNewSize

maxPermSize | -XX:MaxPermSize

newRatio | -XX:NewRatio

newSize | -XX:NewSize

permSize | -XX:PermSize

But somebody can explain me the meaning of NewSize, MaxNewSize, global ARea, maxNewSize, maxPermSize, permSize ?

In what way they are different from heapsize ?

Thanks

kumar

[Former Member]

Hello Kumar,

In Brief, A JVM(Sun/HP - IBM works differently) is divided in the following parts:

Perm Area : Where all the classes are loaded

Heap Area: Where all the objects are loaded.

Heap is inturn dvidided into new area which is also called eden and the tenured area. If the objects are above certain size, they directly are stored in the tenured area. However, otherwise the objects get stored in the new area and are promoted to old/tenured area based on the jvm algorithm/logic during the GCs.

PermSize is the initial size for the perm area.

MaxPermSize is the max that can it be stretched to. We recommend keeping these two same to avoid any dynamic change of the areas.

-Xms is the initial heapsize

-Xmx or MaxHeapSize is the maximum heap that can be allocated. Again, recommendation is to keep both same.

Hope this helps.

Regards,

Snehal/SAP, Palo Alto(USA)

[Former Member]

Hello Kumar,

There is a good thread that explains about the parameters you are looking for. The thread is:

You can also check SAP Note 1303953 (SAP JVM memory parameters and their names in the Config Tool).

Regards,

Jonas Cella

[thunder_feng]

Hi

There is also a general introducation in sap note 723909.

Regards,

Thunder

[fjhernanz]

Hi,

You can find a lot of information about the JVM memoery settings and the parameters meaning just googling a little bit. You can direct to the Oracle website (which bougth Sun and therefore Java), or i.e to:

http://www.docstoc.com/docs/11550777/Java-Garbage-Collection-and-Memory-Architecture

The parameters are explained in that ppt. The note you mention is the recommendation for SAP systems

Br,

Javier