Max Heap Memory on Oracle App Server

We are in the process of upgrading to EnterpriseOne 8.12 w/ TR 8.96.1
We have an Oracle App Server 10g R2 as our HTML / JAS server

The server running this is dual processor 3GHz with 6GB RAM on Windows 2003 Enterprise.

The server is hosting two environments only.

I was wondering whether anyone could provide any guidance on the setting for "Maximum Heap Memory".
At installation, we took the recommendation from a generic (and dated) white paper that set it to 1024MB.

Does anyone know what the considerations are for setting this; and what performance measures we should be checking ?
I have seen some reference to this for Websphere, but little for OAS.

Hi,

Each JAS instance requires a Java Heap (RAM) to process
all user operations and transactions.
In a perfect world, we'd all agree that the more memory
Java Heap has, the better it'll behave.
Alas! In the real world, it doesn't work that way...
Contrarily to C/C++ where it's programmer responsibility
to manage pointers and variables memory (malloc/free),
Java does it automatically for you, so it regularly
runs a cleanup process called "Garbage collection",
which deletes unused memory structures from Java Heap.
The larger the Java memory heap, the longer it will take
to run. So, if Java Heap is too large, it will spend too
much time clearing it up instead of running user processes!
I can't say about OAS, but practical experience told me
that 1 Gb x JAS Instance is a reasonable top limit, while
you shouldn't assign less than 256 Mb RAM.
From SAW interface you can check how much memory is being
used from your Java Heap.
If you have 6 Gb RAM then I'd leave 1.5-2.0 Gb for Windows
and create 4 x 1 Gb RAM JAS Instance, they will run
much better than a single 4 Gb JAS Mammoth instance.

Have a nice day,

I second that. Using multiple instances or JVMs with a smaller footprint will yield better performance over a large footprint, single JVM.

Make sure to always review the Oracle documentation at http://otn.oracle.com for the OAS. With these latest releases of product Oracle has put together some very good documentation.

Re: RE: Max Heap Memory on Oracle App Server

Thanks guys,
Just to clarify, we have 6GB memory on the server
(2GB of which we should reserve for OS)

We only have 2 web environments PY812 and PD812

Are you suggesting two instance per environment - with 1GB assigned to each instance ???

BTW - thanks for the explanation of how the Java Heap memory cleanup works - hadn't come acrosss that before

Re: RE: Max Heap Memory on Oracle App Server

Hi,

Yes, I'd humbly suggest you to create 4 x 1 Gb JAS
instances instead of 2 x 2 Gb ones.
You can assign one for PY and three for PD, assuming that
you have much more people working on PD than on PY.
Have a nice day,