SAP Basis Tech Supports

Symptom

General performance problems are observed for SAP System installations on iSeries. These problems may be caused by incorrectly set OS/400 system values.

Other terms

AS/400, OS/400, iSeries

Reason and Prerequisites

The problem is caused by incorrectly set OS/400 system values.

Solution

You can set the iSeries (former AS/400) operating system OS/400 using system values. Some parameters are of particular importance for the performance. The following are recommendations for some system values:

QBASACTLVL:

Activity Level of the *BASE Pool
Generally one or several SAP Systems are assigned to this memory pool. The minimum size for this system value is:
QBASACTLVL > 1. 2 * (number of work processes of all SAP Systems)
A value that is too high causes a heavier paging. A value that is too low may result in considerable performance problems since jobs change to the ineligible status.
Note: In a 3-tier environment, the local SAP instance work processes and application server shadow processes are usually running on the database server. When calculating QBASACTLVL
(number of work processes for all SAP systems),
the number of shadow processes has to be added up. This means that the following applies to the database server in a 3-tier environment:
QBASACTLVL > 1. 2 * (number of work processes for all SAP Systems +
number of shadow processes for all SAP Systems)

QMAXACTLVL:

Maximum Activity Level of the system
The recommended value is:
QMAXACTLVL = 32727 or *NOMAX

QMCHPOOL:

Size of the *MACHINE memory pools
The minimum size is calculated as:
QMCHPOOL = 1.3 * (16MByte + 2*RAM/32MByte)

RAM is the size of the installed main memory in megabytes. This formula specifies the minimum value for QMCHPOOL. Greater values may be useful in some cases. Generally you should not set lower values. This is only a guide value. A more accurate analysis should include the paging behavior.

QDYNPTYSCD:

Dynamic Priority Scheduler
Activate the Dynamic Priority Scheduler as follows:
QDYNPTYSCD = 1

QPFRADJ:

Performance adjustment
Deactivate the automatic adjustment of the pool sizes and activity levels by:
QPFRADJ = 0

QQRYTIMLMT:

Query processing time limit.
In order to prevent long-running SQL queries terminating early, set:
QQRYTIMLMT = *NOMAX

QACTJOB:

Initial number of active jobs.
Set the following as the initial default value:
QACTJOB = 1000

QADLACTJ:

Additional number of active jobs
If more jobs are necessary than are defined with QACTJOB, this value defines the number of jobs for which the system requests additional main memory.
QADLACTJ = 500

QTOTJOB:

Initial total number of jobs
The default value is:
QTOTJOB = 2000

QADLTOTJ:

Additional number of total jobs
The default value is:
QADLTOTJ = 1000

QJOBMSGQFL:

Job message queue full action
The default value is:
QJOBMSGQFL = *WRAP

QQRYDEGREE:

Parallel processing degree
This value determines the degree of parallel processing for the execution of queries if there is more than one CPU. The default value for an SAP System is:
QQRYDEGREE = *NONE
For a BW system, a separate value for QQRYDEGREE can be useful. For more information, seeSAP Note 307077.

CHGIPLA CPRJOBTBL(*ALL):

Compress job tables
You activate the compression of the job tables to remove unused entries. You can activate the compression with the following command:
CHGIPLA CPRJOBTBL(*ALL)

TCP/IP read/write buffer:

Set TCPRCVBUF and TCPSNDBUF to 1 MB.
The size of the buffer can be set using the OS/400 command CHGTCPA and the parameters TCPRCVBUF and TCPSNDBUF:
CHGTCPA TCPRCVBUF (1048576) TCPSNDBUF (1048576)

To activate these new settings, the TC/IP at least must be restarted (ENDTCP, STRTCP). However, you can also carry out an IPL directly instead.

QAQQINI file:

The database optimizer can be affected using settings in the QAQQINI file. Often specific parameter settings are required in the file for the BW System (seeSAP Note 306823). Sometimes specific settings in the QAQQINI file are recommended because of a certain behavior of the application in the system. In general, the QAQQINI file should be deleted from all libraries (except library QSYS). When you create problem messages, specify whether you have a modified QSYS file in your system.

Expert Cache:

Activate the expert cache for the memory pool where the subsystem of the SAP System runs. In most cases, this is the *BASE pool. You can activate the Expert Cache by displaying the memory pools using command WRKSYSSTS and changing the default value from *FIXED to *CALC in the page break option column.

*INTERACT memory pool:

The subsystems of an SAP System usually run in the *BASE memory pool. The individual work processes then run as a background job. Interactive load is seldom found on the machine. We therefore recommend that you do not configure the *INTERACT memory pool that contains subsystem QINTER. Your SAP system will then have more main storage. Subsystem QINTER should run in the *BASE memory pool.

CAUTION

The aforementioned recommendations are based on our experience. In individual cases, alternative settings of the OS/400 system values can result in a better system behaviour.