SAP Basis Tech Supports

Symptom
Recommended Settings for the IBM JVM for the SAP NetWeaver J2EE Engine on Linux for zSeries.
CAUTION: This note is updated regularly. We recommend that you check it periodically for changes.

Other terms
z/Linux, zLinux, Java Virtual Machine, SDK, JDK, Hybrid JVM, Classic mode, J9 mode
Reason and Prerequisites
On June 2nd, 2009 IBM and SAP released a new IBM 1.4.2 JVM for Linux on System z based on IBM J9 technology
General availability (GA) was announced for the following SAP NetWeaver scenarios:
- SAP NetWeaver 2004 starting with SP22
- SAP NetWeaver 7.0 (2004s) starting with SP15
- SAP NetWeaver 7.0 (2004s) EhP 1 starting with SP3
- SAP NetWeaver 7.0 (2004s) EhP 2 and future EhP’s
For details please see SAP Note 1338196.
For technical details how to run the IBM 142 SR13 JVM in J9 mode please see SAP Note 1319038.
For other SAP NetWeaver releases you have to run the IBM 142 JDK SR13 in
Classic mode as you did before.
For this mode the following recommendations are still valid.
Millicode prerequisites for zSeries z990(Machine type 2084) and z9 (Mach
There is a millicode patch which has to be installed to solve a store ordering problem when using Java shared variables defined with “volatile”:
For z990, it is Driver-55: MCL232 in the J13484 (i390/ML) Stream.
For z9, it is Driver-67: MCL065 in the G40963 (i390/ML) Stream.
Starting with 142 SR12 the latest JCE Policy Files are required!
https://www14.software.ibm.com/webapp/iwm/web/preLogin.do?source=jcesdk
New prerequisite for JDK 142 SR13:
SAP Note 1306760 has to be implemented for the 142 SR13 installation
(Introducing missing iiop functionality for IBM 1.4.2SR13JDK)
Solution
General Recommendations
Make sure that you have installed the required SDK.
You can verify this requirement by running ‘java -fullversion’.
The version and build information in the output text must be:
“J2RE 1.4.2 IBM build cxz64142-20090307 (SR13)”)
You have to download the SDK 1.4.2 ServiceRelease 13 from the download site “IBM Java for ISVs”:
https://www14.software.ibm.com/webapp/iwm/web/preLogin.do?lang=en_US&source=swg-ibmjavaisv
The access key for SAP is AQ2QQK45DQ
First you have to sign in with your IBM user ID .
If you do not yet have an IBM user ID, please register at the IBM registration site:
https://www.ibm.com/account/profile/us?page=reg
If the links don’t work, please check for a superfluous space within the URL string.
After login go to paragraph “IBM SDK for Linux on 64-bit zSeries ” and download:
the rpm format “IBMJava2-142-z64-SDK-1.4.2-13.0.s390x.rpm” or
the tgz format of the SDK “IBMJava2-SDK-1.4.2-13.0.s390x.tgz”.
After the SDK upgrade you have to install the “Unlimited Strength Jurisdiction Policy Files” manually again, because these are overwritten during the SDK upgrade (see SAP Note 754699, 739043).
Starting with 142 SR12 the latest JCE Policy Files are required!
https://www14.software.ibm.com/webapp/iwm/web/preLogin.do?source=jcesdk
Recommended Settings (”-Xnopartialcompactgc” has been removed):
Currently we recommend the following settings for the J2EE server(s) (to be set with the configtool)
‘cluster-data’->’instance_IDxxxxxxx’->’server_IDxxxxxxxxx’-> General
-Xms2048M
initial heap size
-Xmx2048M
maximum heap size
-Xconcurrentbackground1
controls how many background helper threads participate in GC. Must be
equal to the number of processors in an SMP or LPAR. The default value is
1 .
-Xloratio0.3
controls how much of the total heap ( -Xmx setting ) is reserved for
large objects. Default is 0.05, reserving 5% .
-Xparroot
enables early, parallel scanning of roots to shorten GC pause times
-Xconcurrentlevel6
controls the timing of starting concurrent GC work
-XSoftRefThreshold0
controls how many GC cycles objects kept alive by softreferences survive
-Xconmeter2
instructive parameter for the concurrent GC accurate triggering and
metering
-Xk32000
the maximal number of classes the kCluster will contain, default is 1280
(each of 256 bytes). kCluster – 1st object of the heap
-verbose:Xgccon
GarbageCollector output inclusive additional mostly concurrent data
-Xdisableexplicitgc
to prevent superfluous System GCs triggered by the application
‘cluster-data’->’instance_IDxxxxxxx’->’Message Server & Bootstrap’:
-Xmx1024M
maximum heap size
‘cluster-data’->’instance_IDxxxxxxx’->’dispatcher_IDxxxxxxxxx’-> ‘General’:
-Xms200M
initial heap size
-Xmx200M
maximum heap size -verbose:Xgccon
GarbageCollector output inclusive additional mostly concurrent data
Other Settings
In case you can’t create a Java Dump (javacore..txt) by sending SIGQUIT
to the dispatcher/server process with “kill -3 jlaunch_pid” or using SAP
utility “jcmon”, then you have to set
environment variable IBM_SAP_SIGQUIT_JAVACORE to true and (re)start the J2EE server.
setenv IBM_SAP_SIGQUIT_JAVACORE true
or
export IBM_SAP_SIGQUIT_JAVACORE=true
If you find a parameter like
-Djava.compiler=NONE
remove this entry from the settings. .
During deployment, some Java files may not be compiled because the
default heapsize of 64 MB is too small for the Java compiler javac.
You see : java.lang. OutOfMemory – the system is out of memory
(visible in SDM if sda/sca is being deployed).
You find the solution for this problem in SAP note 759669 .
In case the J2EE Engine dumps with a Javacore file stating “signal xx
received”, you need to prepare your system to get the right error
documentation for SAP/IBM support. Please follow the instructions in
SAPNote 852567. If you disable the SAP signal handler you also have to
switch off the signal handler of the IBM JVM by setting the
environment variable “IBM_NOSIGHANDLER” to “TRUE” prior to starting
the J2EE server.
If you run DTR or XI and the J2EE engine abends with
NullPointerException, then you find the solution in SAP Note 859465. This problem is fixed with 142 SR4-1 .
We are going to change the above recommendations in the future as soon
as better option set has been elaborated. Please check this note
periodically for changes.

JDK history:
28Apr09 cxz64142-20090307 (SR13) solves following problems:
- Remove duplicate entries in java.library.path
- JVM crash (Signal 11 in method fixupQuickInvocation)
Prerequisite to install SR13 is the implementation of SAP Note 1306760 (Introducing missing iiop functionality for IBM 1.4.2 SR13 JDK)