SAP Basis Tech Supports

Symptom
You convert your Web Application Server Java in such a way that it no longer uses the IBM Classic VM 1.4.2, but uses the new IT4J VM 1.4.2 64bit (J9) instead.
Other terms
AS/400, iSeries, classic, IT4J, J9, switch tool, CONFIGJVM IT4J
Reason and Prerequisites
As of IBM i 6.1, the IBM IT4J VM 1.4.2 64bit is offered in addition to the IBM Classic VM 1.4.2. The Classic VM 1.4.2 is no longer available as of the next highest operating system release.
Solution
This note is a more simple guide to performing the conversion.
Sections of the note:
1.Prerequisites for the conversion2.Preparing the conversion3.Using CONFIGJVM for the conversion4.Detailed description of the conversion

1.Prerequisites for the conversion
To perform the conversion successfully, your system that is to be converted must fulfil the following prerequisites:
You must install theproduct option 13of the IBM i 6.1 license program5761JV1. If this product option is not part of your IBM i 6.1 installation, you can subsequently order this using a purchase order ofPTF SI32444. In addition, all PTFs of the currentINFOAPARfor SAP of the current operating system version must be entered for in the operating system. Refer toNote 144149for details.Thekernel of the SAP systemmust have the most current status. In detail, you must ensure that at least the following patches are applied:
Kernel 6.40SAPJ2EE # 28MENUS # 5R3INLPGM #36CONFIGJVM # 1
Kernel 7.00SAPJ2EE # 45MENUS # 5R3INLPGM #30CONFIGJVM # 1
Thesoftware level of the Java stacksmust fulfil the following minimum requirements:
6.40:at least JavaSupport Package Stack 18
7.00:at least JavaSupport Package Stack 162.Preparing the conversion
The tool for the conversion (CONFIGJVM) sets the heap for Java objects to 2GB for existing server nodes. This may restrict the system capacity if the system already runs at a high load. For this reason, determine the actual heap used by the system with the Classic JVM before the conversion, and add new server nodes if required.
You can determine the actual heap by opening the file std_server<number>.out in the directory /usr/sap/<SID>/<Instanz>/work and searching for garbage collectors with the following pattern:
GC <number>: current heap(KB) <number>; current threshold(KB) <number>.
The figure for current heap(KB) defines how many KB of the actual Java heap are required. You should use the determined maximum value as a guide.
If you use several server nodes, you must add up the maximum values of the individual nodes.
The rule of thumb for the number of required server nodes with IT4J is therefore:
#(server nodes) = maximum current heap (GB) / 2GB
The rounded result is the recommended number of server nodes.
If you have to add server nodes, you can add these at any time, before or after the conversion. You can use the configtool for that. If you add server nodes after the conversion using the configtool, we recommend that you run CONFIGJVM again, with the option KEEPHEAP(*YES) (if required) to prevent existing Java Heap settings of other nodes from being overwritten.
3.Using CONFIGJVM for the conversion
Use the tool CONFIGJVM to perform the conversion. It is automatically part of the kernel if all of the above prerequisites are fulfilled.
The tool is available from the SAP main menu in the submenu
“7. Define or Change SAP” and then
“4. SAP Java Stack”.
The system switches to IT4J automatically during the call of
“2. Configure VM Options – Apply”
if you use IBM i Release 6.1 or higher. In this case, you must ensure that the Java stack is shutdown when you perform the switch. When you restart, the system then uses the new IT4J VM.
Note 1262494 contains a more detailed description of the functions and the handling of CONFIGJVM.
4.Detailed description of the conversion
The changes that are implemented by CONFIGJVM are implemented using certain rules. If required, you must judge whether the results of the preview are acceptable.
CONFIGJVM basically implements the specifications that are described in Note 1234382.
If the CONFIGJVM tool is not available but you want to convert to IT4J, you can implement the relevant changes manually by making adjustments in various profile and property files and by using the config tool to adjust the server and dispatcher nodes:
Instance profile:
You must set the parameter jstartup/vm/home to the value /QOpenSys/QIBM/ProdData/JavaVM/jdk14/64bit.
Server and dispatcher configuration:
Use the config tool to implement the changes. Ensure that, in particular, the following parameters are correctly configured in accordance with Note 1234382.
-Xmx (Max heap size)
-Xms
-Xmn
-Xgcpolicy
-Xdisableexplicitgc
-Xsoftrefthreshold0
-Xlp64k
-Djava.ext.dirs
-Djava.awt.headless
In addition, you must delete the parameters that were relevant only for the IBM Classic VM. These are usually the parameters that begin with -Dos400.
Before you restart with a new VM, you must also delete the file <dir_instance>/j2ee/cluster/instance.properties.vmprop. This file is rewritten by the startup framework when you start the system. If it exists with incorrect data, it may lead to problems when you start the system.
The file <dir_instance>/j2ee/cluster/instance.properties is usually adjusted by the bootstrapping when you start the system. This means that you do not have to change this file. However, it may be the case that values are still entered in the settings for the bootstrp process and this prevents the system start. You must manually change this.
SDM configuration:
You must convert the JavaPath and Heap Size parameters in the following SDM files in accordance with Note 1234382:
<dir_instance>/SDM/program/config/sdm_jstartup.properties
<dir_instance>/SDM/program/sdm_jdk.sh
You must delete the file <dir_instance>/SDM/program/config/sdm_jstartup.properties.vmprop if it is available.