(ZOS) z/OS operating system tuning tips

There are several configuration changes we can make to z/OS system components that might improve product performance.

We might want to make one or more of the following changes to the indicated z/OS components:

• CTRACE

  The first place to review is your CTRACE configuration. Ensure that all components are either set to MIN or OFF. To display the CTRACE options for all components on the system, issue the following command from the operator console:

  D TRACE,COMP=ALL
  

  To change the setting for an individual component to its minimum tracing value. where xxx is the component ID.

  TRACE CT,OFF,COMP=xxx
  

  This configuration change eliminates the unnecessary overhead of collecting trace information that is not needed. Often during debug, CTRACE is turned on for a component and not shut off when the problem is resolved.
• SMF

  Ensure that we are not collecting more SMF data than we need. Review the SMFPRMxx settings to ensure that only the minimum number of records are collected.

  Use SMF 92 or 120 only for diagnostics.

  • SMF Type 92

    SMF Type 92 records are created each time an HFS file is opened, closed, deleted, and so forth. Almost every web server request references HFS files, so thousands of SMF Type 92 records are created. Unless you specifically need this information, turn off SMF Type 92 records. In the following example, we have disabled the collection of SMF type 92 records:

    Example:

     ACTIVE,  
     DSNAME(SYS1.&.SYSNAME..SMF.MAN1;SYS1.&SYSNAME..SMF.MAN2;),          
     NOPROMPT,   
     REC(PERM),   
     MAXDORM(3000),  
     STATUS(010000), 
     JWT(0510),     
     SID(&SYSNAME;(1:4)),  
     LISTDSN,           
     SYS(NOTYPE(19,40,92)),    
     INTVAL(30), 
     SYNCVAL(00),  
     SYS(DETAIL,INTERVAL(SMF,SYNC)),   
     SYS(EXITS(IEFACTRT,IEFUJI,IEFU29,IEFU83,IEFU84,IEFU85,IEFUJV,IEFUSI))
    
    

  • SMF Type 120

    We might find that running with SMF 120 records in production is appropriate, because these records give information specific to applications running on the product, such as response time for Enterprise Edition (Java EE) artifacts, bytes transferred, and so forth. If we do choose to run with SMF 120 records enabled, we should use server interval SMF records and container interval SMF records rather than server activity records and container activity records.

    bprac

    To enable specific record types in the administrative console, specify the following properties:

    • server_SMF_server_activity_enabled=0 (or server_SMF_server_activity_enabled = false), which turns off SMF Subtype 1: Server activity record.
    • server_SMF_server_interval_enabled=1 (or server_SMF_server_interval_enabled = true), which turns on SMF Subtype 3: Server interval record.
    • server_SMF_container_activity_enabled=0 (or false), which turns off SMF Subtype 5: J2EE container activity record (v2).
    • server_SMF_container_interval_enabled=1 (or true), which turns on SMF Subtype 6: J2EE container interval record (v2).
    • server_SMF_request_activity_enabled=1 (or true), which turns on SMF Subtype 9: Request Activity record.

      Because of the size of this record type, there is a performance impact when we are running this record. Therefore, when we run this record, we might want to turn off the collection of data for certain sections if we do not need that information. Turning off the collection of data for the sections that we do not need lessens the performance impact. See the description of the SMF 120 Type 9 record for more information on which sections can be turned off, and how to turn them off.bprac

    • server_SMF_outbound_enabled (or true), which turns on SMF Subtype 10: Outbound Request records.
    • server_SMF_interval_length=1800.

• We might also want to review your DB2 records and the standard RMF™ written SMF records, and ensure that the SMF data sets are allocated optimally. DB2 SMF records 100, 101 and 102 affect performance and should be used only for monitoring DB2 performance with the DB2 PM tool. If we are not monitoring DB2 performance, we should consider not collecting those SMF records.

Enable SMF recording

Use the administrative console to enable properties for specific SMF record types

SMF Subtype 1: Server activity record

SMF Subtype 3: Server interval record

SMF Subtype 5: J2EE container activity record (v2)

SMF Subtype 6: J2EE container interval record (v2)

SMF Subtype 9: Request Activity record

SMF record type 120 (78) - WAS performance statistics