How to resolve java dispatcher startup issues?

This article answers following queries:

How to resolve java dispatcher startup issues?

What checks need to be done if java dispatcher doesn’t start during java startup?

What action need to be performed to fix java dispatcher startup issues?

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If java dispatcher doesn’t start during java startup, please check the std_dispatcher log from java work directory. It means, go to /usr/sap/<SID>/<instance>/work directory and look out for error messages. If you find below error message, this could be due to conflict between values maintained for thread mananger.

Loading: ThreadManager returned false! Kernel not loaded. System halted.

To resolve this issue, please proceed as follows:

•  Please login to config tool
•  Navigate to config tool -> dispatcher -> managers -> threadmanager
•  Please verify the values maintained for MinThreadCount, InitialThreadCount   and  MaxThreadCount.
•  Please make sure that MinThreadCount value <= InitialThreadCount <=    MaxThreadCount
•  If you are not sure about the values to be set, please maintain default values and check if dispatcher starts

If issue, didn’t get resolved even after performing above steps, please perform below mentioned additional tasks and retry to start the system

• In Config tool, navigate to Cluster-data --> Instance_IDxx --> dispatcher_IDxx --> managers --> ConfigurationManager
• In the local properties section, please make sure sqljdbc.jar exists for rdbms.driverLocation

Explain Java Virtual Memory in SAP

This article answers following queries :

• Explain memory management of Java Virtual Machine(JVM) in SAP

• Explain JVM memory areas in SAP

• Explain Young generation, Tenured generation and Permanent Generations

• How to maintain JVM parameters  in SAP?

• Which tool is used to configure Java VM settings in SAP?

• How JVM automatically takes care of memory allocation?

• Explain Used memory, Allocated memory, Virtual memory

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The JVM automatically takes care of allocation of memory space for java applications.

A “generation” reserves space in the address area of the host.

While starting sap system, the java virtual machine allocates operating system memory for each of the generations. This initially allocated memory is termed as “initial” or “initial size”. After complete usage of initial size, the java virtual machine further allocates memory in stages upto a maximum defined value termed as “max size”.

The memory space that is available is called the available memory or allocated memory. Since this space is reserved by the operating system, it is also called as “reserved space”. The space that is not reserved is called as “virtual memory”. 

The “ reserved space”  is available to the JVM. However, not all the memory is used always. It will be used based on the requirement. The memory that is actually used by the java applications is termed as “used memory”. If less space is required by the java application, the memory is returned to the operating system in stages. 

The memory area of JVM is mainly divided into 3 areas as listed below

• Young generation

• Tenured generation

• Permanent generation

The 3 memory areas Young, Tenured and Permanent differ based on the data stored in them. Each of these generations has an initial and maximum size.

Young Generation : The objects that have been newly created by the applications are stored in the younger generation.

For younger generation, we can define initial size and maximum size with the parameters  -XX:NewSize and –XX:MaxNewSize respectively

 Tenured Generation: The objects that have been required for a longer period of time by an application are automatically moved to the tenured generation

For tenured generation, we cannot directly set initial size and maximum size directly. These are calculated from the parameters of the younger generation and the parameters  –Xms and  –Xmx.

The parameter –Xms is the “start heap size” or “initial heap size” and it defines the total initial size of the young and tenured generations.

The parameter  -Xmx is the “max heap size” and it defines the total size of the young and tenured generations.

So indirectly, it means that 

Initial size of tenured generation =  (-Xms)  -  (-XX:NewSize)

Maximum size of tenured generation = (-Xmx) – (–XX:MaxNewSize)

Permanent Generation : The objects that are permanently required by the JVM such as classes and objects are stored in the Permanent Generation.

For permanent generation, we can define initial size and maximum size with the parameters –XX:PermSize and  –XX:MaxPermSize respectively

Config Tool is the only tool used to set JVM parameters in an SAP java system.

How to open Config tool ?

This article answers the following queries:

• How to open config tool in SAP (for offline configuration) ?
• What is the process to be followed to access config tool in SAP ?
• How to open config tool in Microsoft windows environment?
• How to open config tool in  Unix (AIX , HP-UX etc) environment?

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Config tool is mainly used to set JVM parameters in SAP.

In this article, am covering on how to open config tool (with screenshots)  in Microsoft windows environment :

Goto respective drive and navigate as follows

usr  -> sap  ->  <SID>  -> DVEBMGS**  ->  j2ee  ->  configtool    (shown in below figure)

and double click on configtool.bat file.

This run a batch file and opens up another screen as follows and prompts you to confirm whether you want to use default DB settings.

Click on Yes and confirm the same.

This opens up  config tool, where various parameters can be viewed/maintained

 

Procedure of opening config tool  in Unix is same as above.

i)              To be navigated to /usr/sap/<SID>/DVEBM*/J2ee/Configtool

ii)            Execute ./configtool.sh script

This opens up the config tool as above.

Note : Only difference is here, script need to be run instead of a bat file in windows.

Related Link :

What is the difference between config tool and visual administrator?

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What is the difference between Config Tool and Visual Administrator tools in SAP?

This article answers the below queries :

• What are the prerequisites and uses of  config tool ?
• What are the prerequisites and uses of Visual Administrator ?
• What are the limitations of Config tool ?
• What is the difference between Config Tool and Visual Administrator tools in SAP?

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Config Tool and Visual Administrator(VA) are the administration and configuration tools in SAP Netweaver AS Java.

What are the prerequisites and uses of  config tool ?

The prerequisite for the config tool is database must be running, as this tool is  used to maintain the SAP Netweaver AS Java settings in the database. It is not necessary that Java should be running to use config tool.

Uses of config tool :

• The Java Virtual Memory(JVM) settings can only be maintained with the config tool.

• Configuration of services and managers can be done with config tool

Limitations of Config tool :

• Remote configuration cannot be done by Config tool

• Start or stop of java cannot be done through config tool

• Change of parameters at run time is not possible

What are the prerequisites and uses of Visual Administrator ?

With visual administrator, we can logon to the P4 port of the AS Java. Hence both database and java should be running. This is the prerequisite for VA.

Uses of Visual Administrator :

• Configuration of services and managers can be done
• Remote configuration can be done ( It means VA can be installed and used for configuration in any host on which SAP Netweaver AS JAVA is not installed
• Starting and stopping services can be done
• Stopping an SAP NW As java instance can be done

What is the difference between Config Tool and Visual Administrator tools in SAP?

• Java Virtual Machine parameter settings can only be done through Config tool. VA cannot be used for this
• To use VA, SAP Netweaver AS Java should  be running but for config tool it is not required
• Changes to selected parameters can be done at run time through VA, which is not possible with Config tool.
• AS Java can be started/stopped by VA which is not possible by Config tool
• Remote configuration can be done by VA but not by config tool

Related Link :

How to open config tool?